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Old 7th December 2006, 17:38   #11
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Rover 75 CDTi Conn. SE

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Default The Fuel and Engine Bible

Everything you need to know about engines and fuel.


My Rover 75 after i did the latest mods
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Old 21st December 2006, 18:44   #12
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Default Alloy wheel refurbishers

Alloy wheel refurbishers
Supplied by Keith and Kearton
A few links normally rules apply, this is for information only not endorsed by the club etc.

http://www.wickedwheels.co.uk (mobile)

Last edited by GreyGhost; 10th March 2008 at 21:57..
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Old 5th February 2007, 14:12   #13
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Default O2 Sensors and how they work

The following threads may prove useful, they may be a bit dated and the info is not 75/ZT specific but for reference :-

Today’s computerized engine control systems rely on inputs from a variety of sensors to regulate engine performance, emissions and other important functions. The sensors must provide accurate information otherwise driveability problems, increased fuel consumption and emission failures can result.
One of the key sensors in this system is the oxygen sensor. It’s often referred to as the "O2" sensor because O2 is the chemical formula for oxygen (oxygen atoms always travel in pairs, never alone).
The first O2 sensor was introduced in 1976 on a Volvo 240. California vehicles got them next in 1980 when California’s emission rules required lower emissions. Federal emission laws made O2 sensors virtually mandatory on all cars and light trucks built since 1981. And now that OBD-II regulations are here (1996 and newer vehicles), many vehicles are now equipped with multiple O2 sensors, some as many as four!
The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust as the exhaust exits the engine. Monitoring oxygen levels in the exhaust is a way of gauging the fuel mixture. It tells the computer if the fuel mixture is burning rich (less oxygen) or lean (more oxygen).
A lot of factors can affect the relative richness or leanness of the fuel mixture, including air temperature, engine coolant temperature, barometric pressure, throttle position, air flow and engine load. There are other sensors to monitor these factors, too, but the O2 sensor is the master monitor for what’s happening with the fuel mixture. Consequently, any problems with the O2 sensor can throw the whole system out of whack.

The computer uses the oxygen sensor’s input to regulate the fuel mixture, which is referred to as the fuel "feedback control loop." The computer takes its cues from the O2 sensor and responds by changing the fuel mixture. This produces a corresponding change in the O2 sensor reading. This is referred to as "closed loop" operation because the computer is using the O2 sensor’s input to regulate the fuel mixture. The result is a constant flip-flop back and forth from rich to lean which allows the catalytic converter to operate at peak efficiency while keeping the average overall fuel mixture in proper balance to minimize emissions. It’s a complicated setup but it works.
When no signal is received from the O2 sensor, as is the case when a cold engine is first started (or the 02 sensor fails), the computer orders a fixed (unchanging) rich fuel mixture. This is referred to as "open loop" operation because no input is used from the O2 sensor to regulate the fuel mixture. If the engine fails to go into closed loop when the O2 sensor reaches operating temperature, or drops out of closed loop because the O2 sensor’s signal is lost, the engine will run too rich causing an increase in fuel consumption and emissions. A bad coolant sensor can also prevent the system from going into closed loop because the computer also considers engine coolant temperature when deciding whether or not to go into closed loop.

The O2 sensor works like a miniature generator and produces its own voltage when it gets hot. Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb. The bulb is coated on the outside with a porous layer of platinum. Inside the bulb are two strips of platinum that serve as electrodes or contacts.
The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors "breathe" through their wire connectors and have no vent hole. It’s hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail. The difference in oxygen levels between the exhaust and outside air within the sensor causes voltage to flow through the ceramic bulb. The greater the difference, the higher the voltage reading.
An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor’s output voltage will drop down to about 0.1 volts. When the air/fuel mixture is balanced or at the equilibrium point of about 14.7 to 1, the sensor will read around 0.45 volts.
When the computer receives a rich signal (high voltage) from the O2 sensor, it leans the fuel mixture to reduce the sensor’s reading. When the O2 sensor reading goes lean (low voltage), the computer reverses again making the fuel mixture go rich. This constant flip-flopping back and forth of the fuel mixture occurs with different speeds depending on the fuel system. The transition rate is slowest on engines with feedback carburetors, typically once per second at 2500 rpm. Engines with throttle body injection are somewhat faster (2 to 3 times per second at 2500 rpm), while engines with multiport injection are the fastest (5 to 7 times per second at 2500 rpm).
The oxygen sensor must be hot (about 600 degrees or higher) before it will start to generate a voltage signal, so many oxygen sensors have a small heating element inside to help them reach operating temperature more quickly. The heating element can also prevent the sensor from cooling off too much during prolonged idle, which would cause the system to revert to open loop.
Heated O2 sensors are used mostly in newer vehicles and typically have 3 or 4 wires. Older single wire O2 sensors do not have heaters. When replacing an O2 sensor, make sure it is the same type as the original (heated or unheated).

Starting with a few vehicles in 1994 and 1995, and all 1996 and newer vehicles, the number of oxygen sensors per engine has doubled. A second oxygen sensor is now used downstream of the catalytic converter to monitor the converter’s operating efficiency. On V6 or V8 engines with dual exhausts, this means up to four O2 sensors (one for each cylinder bank and one after each converter) may be used.
The OBD II system is designed to monitor the emissions performance of the engine. This includes keeping an eye on anything that might cause emissions to increase. The OBD II system compares the oxygen level readings of the O2 sensors before and after the converter to see if the converter is reducing the pollutants in the exhaust. If it sees little or no change in oxygen level readings, it means the converter is not working properly. This will cause the Malfunction Indicator Lamp (MIL) to come on.

O2 sensors are amazingly rugged considering the operating environment they live in. But O2 sensors do wear out and eventually have to be replaced. The performance of the O2 sensor tends to diminish with age as contaminants accumulate on the sensor tip and gradually reduce its ability to produce voltage. This kind of deterioration can be caused by a variety of substances that find their way into the exhaust such as lead, silicone, sulfur, oil ash and even some fuel additives. The sensor can also be damaged by environmental factors such as water, splash from road salt, oil and dirt.
As the sensor ages and becomes sluggish, the time it takes to react to changes in the air/fuel mixture slows down which causes emissions to go up. This happens because the flip-flopping of the fuel mixture is slowed down which reduces converter efficiency. The effect is more noticeable on engines with multiport fuel injection (MFI) than electronic carburetion or throttle body injection because the fuel ratio changes much more rapidly on MFI applications. If the sensor dies altogether, the result can be a fixed, rich fuel mixture. Default on most fuel injected applications is mid-range after three minutes. This causes a big jump in fuel consumption as well as emissions. And if the converter overheats because of the rich mixture, it may suffer damage. One EPA study found that 70% of the vehicles that failed an I/M 240 emissions test needed a new O2 sensor.
The only way to know if the O2 sensor is doing its job is to inspect it regularly. That’s why some vehicles (mostly imports) have a sensor maintenance reminder light. A good time to check the sensor is when the spark plugs are changed.
You can read the O2 sensor’s output with a scan tool or digital voltmeter, but the transitions are hard to see because the numbers jump around so much. Here's where a PC based scantool such as AutoTap really shines. You can use the graphing features to watch the transitions of the O2 sensors voltage. The software will display the sensor’s voltage output as a wavy line that shows both it’s amplitude (minimum and maximum voltage) as well as its frequency (transition rate from rich to lean).
A good O2 sensor should produce an oscillating waveform at idle that makes voltage transitions from near minimum (0.1 v) to near maximum (0.9v). Making the fuel mixture artificially rich by feeding propane into the intake manifold should cause the sensor to respond almost immediately (within 100 milliseconds) and go to maximum (0.9v) output. Creating a lean mixture by opening a vacuum line should cause the sensor’s output to drop to its minimum (0.1v) value. If the sensor doesn’t flip-flop back and forth quickly enough, it may indicate a need for replacement.
If the O2 sensor circuit opens, shorts or goes out of range, it may set a fault code and illuminate the Check Engine or Malfunction Indicator Lamp. If additional diagnosis reveals the sensor is defective, replacement is required. But many O2 sensors that are badly degraded continue to work well enough not to set a fault code—but not well enough to prevent an increase in emissions and fuel consumption. The absence of a fault code or warning lamp, therefore, does not mean the O2 sensor is functioning properly.

Any O2 sensor that is defective obviously needs to be replaced. But there may also be benefits to replacing the O2 sensor periodically for preventive maintenance. Replacing an aging O2 sensor that has become sluggish can restore peak fuel efficiency, minimize exhaust emissions and prolong the life of the converter.
Unheated 1 or 2 wire wire O2 sensors on 1976 through early 1990s vehicles can be replaced every 30,000 to 50,000 miles. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications can be changed every 60,000 miles. On OBD II equipped vehicles (1996 & up), a replacement interval of 100,000 miles is recommended.

Last edited by Keith; 5th February 2007 at 14:24..
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Old 5th February 2007, 14:14   #14
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Default Diagnosing Misfires

Misfire is a common driveability problem that may or may not be easy to diagnose, depending on the cause. A misfiring cylinder in a four-cylinder engine is, pardon the pun, hard to miss. The loss of 25% of the engine's power output is the equivalent of a horse trying to run on three legs. The engine may shake so badly at idle that it causes vibrations that can be felt in the steering wheel and throughout the vehicle. The engine also may be hard to start and may even stall at idle, depending on the accessory load (air conditioning, headlights and electric rear defroster, for example).
When misfire occurs, performance suffers along with fuel economy, emissions and idle quality. And, when a misfiring vehicle is subjected to an emissions test, it will usually fail because of the unusually high levels of hydrocarbons (HC) in the exhaust.
What causes a cylinder to misfire? Basically, it's one of three things: loss of spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression. Loss of spark includes anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. Causes include worn, fouled or damaged spark plugs, bad plug wires or even a cracked distributor cap. A weak coil or excessive rotor gas inside a distributor would affect all cylinders, not just a single cylinder.
"Lean misfire" can occur when the air/fuel mixture is too lean (not enough gasoline in the mixture) to burn. This can be caused by a dirty, clogged or inoperative fuel injector; air leaks; or low fuel pressure because of a weak pump, restricted filter or leaky pressure regulator. Low fuel pressure would affect all cylinders rather than an individual cylinder, as would most air leaks. A leaky EGR valve can also have the same effect as an air leak.
Loss of compression means the cylinder loses most of its air/fuel mixture before it can be ignited. The most likely causes here are a leaky (burned) exhaust valve or a blown head gasket. If two adjacent cylinders are misfiring, it's likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant, it's likely the head gasket is the culprit.
Intermittent misfires are the worst kind to diagnose because the misfire comes and goes depending on engine load or operating conditions. They seem to occur for no apparent reason. The engine may only misfire and run rough when cold but then smooth out as it warms up. Or, it may start and idle fine but then misfire or hesitate when it comes under load. Also, it may run fine most of the time but suddenly misfire or cut out for no apparent reason. Intermittent misfires can be a real challenge to diagnose, so let's start with a steady misfire in one cylinder before moving on to intermittent misfires.

In the case of a steady misfire, isolating the misfiring cylinder is the first step in diagnosing the problem. Today's OBDII systems make this easy using a scantool such as AutoTap. Simply use AutoTap to read the Diagnostic Trouble Code (DTC) stored in the PCM.
This is preferable to the traditional method of pulling plug wires to identify the weak cylinder, because it prevents the voltage from causing any damage to the electronics in the ignition system. When a plug wire is physically disconnected from a spark plug, the high voltage surge from the coil cannot follow its normal path to ground through the plug wire and spark plug, so it passes back through the coil. Most ignition systems are robust enough to withstand such voltage backups intermittently but not on a prolonged basis. If the coil or ignition module is already weak, it may push the component over the brink causing it to fail.

So, now you've diagnosed a misfire and have isolated it to one cylinder. Many times, the cause will be obvious when you remove the spark plug. If the plug's insulator is cracked or broken, you've found the problem. If the plug appears to be OK but is wet, inspect the plug wire and boots for damage. Measure the plug wire's resistance, end to end, with an ohmmeter. Refer to the vehicle manufacturer's specifications, but, as a rule, resistance should not exceed 8,000 ohms per foot. Replace the wire if resistance exceeds specifications. If the plug is fouled, you've found the source of the misfire, but you still have to determine what caused the plug to foul. Heavy black oily carbon deposits would tell you that the engine is burning oil. The most likely cause is worn valve guide seals and/or guides, but worn rings and cylinders can also allow oil to enter the combustion chamber. Replacing the spark plug will temporarily cure the misfire problem, but, until the oil consumption problem is fixed, the engine will continue to foul plugs.
A leakdown or compression test will help you determine if the oil is getting past the valve guides or the rings. If the cylinder shows little leakdown or holds good compression when a little oil is squirted into the cylinder (wet compression test), it would tell you that the engine needs new valve guide seals and/or guide work. Most late model import engines have positive valve guide seals. Often, the guides are fine, but the seals are worn or cracked. The seals can be replaced on some engines without too much effort and without having to remove the head.
Just pull off the valve cover, remove the valvetrain hardware and use an external spring compressor to remove the springs so new seals can be installed. A regulated air hose connected to the spark plug hole will keep the valve from dropping into the cylinder. But, on many OHC engines, there's so much disassembly involved to get to the valve springs you're better off removing the head.
A spark plug that shows heavy whitish to brown deposits may indicate a coolant leak either past the head gasket or through a crack in the combustion chamber. This type of problem will only get worse and may soon lead to even greater problems if the leak isn't fixed. Coolant makes a lousy lubricant and can cause ring, cylinder and bearing damage if it gets into a cylinder or the crankcase. Loss of coolant can also lead to overheating, which may result in cracking or warping of aluminum cylinder heads. If you suspect this kind of problem, pressure test the cooling system to check for internal coolant leakage. Spark plugs that show preignition or detonation damage may indicate a need to check timing, the operation of the cooling system and conditions that cause a lean air/fuel mixture. You might also want to switch to a colder heat range plug.
Short trip stop-and-go driving can cause a rapid buildup of normal deposits on plugs, especially if the engine has a lot of miles and there has been some oil leakage past the valve guide seals and rings. The cure here might be to switch to a one-step hotter spark plug.
If the spark plug and plug wire are OK but the cylinder is weak, a leakdown or compression test should be done to determine if the problem is compression related. The exhaust valves are the ones most likely to lose their seal and leak compression, so, if you find unusually low compression, follow up with a wet compression test to determine if the problem lies with the valves or rings. No change in compression with a wet test would tell you the problem is valve related (probably a bad exhaust valve) or a blown head gasket. But, if the compression readings are significantly higher with a wet compression test, it would tell you the piston rings and/or cylinder walls are worn. Either way, you are looking at major repairs. The only cure for a leaky valve is a valve job, and the only cure for a leaky head gasket is to replace the gasket. Likewise, the only cure for worn rings and cylinders is to overhaul or replace the engine.
Low compression can also be caused by a rounded cam lobe. If the valve doesn't open, the cylinder can't breathe normally and compression will be low. A visual inspection of the valvetrain and cam will be necessary if you suspect this kind of problem.

If the ignition components and compression in a misfiring cylinder are fine, that leaves fuel (or the lack thereof) as the only other possibility. You can start by checking for voltage at the injector. A good injector should also buzz while the engine is running. No buzzing would tell you the injector is dead, while a no-voltage reading would tell you it isn't the injector's fault but a wiring or computer driver problem.
If the injector is buzzing and spraying fuel but the cylinder isn't getting enough fuel, the injector is dirty or clogged. On-car cleaning may help remove the varnish deposits that are restricting the injector and restricting fuel delivery.
If you're dealing with a random misfire that can't be isolated to a particular cylinder, all the injectors may be dirty. You should also check fuel pressure to see if the pump is weak or the pressure regulator is defective. A plugged fuel filter can reduce fuel pressure. If fuel pressure is within specifications, check the intake vacuum to see if there is an air leak that's upsetting the overall air/fuel mixture. A couple of overlooked causes here may be a leaky EGR valve or a leaky power brake booster.

What will a scan tool tell you about misfire? Not much unless the vehicle is equipped with OBDII (1996 or newer). When the OBD II system detects a misfire that exceeds "normal" limits, it illuminates the Check Engine light and sets a P-code that corresponds to the misfiring cylinder. The last number in a P300 series code tells you which cylinder is misfiring. A code P304, for example, says cylinder number four is misfiring. If you also find a P204 code (P200 series codes cover the injectors), you'd know the misfire was probably caused by a bad injector.
If you find a P300 code, it means the misfire is random and is moving around from cylinder to cylinder. The cause here would likely be something that upsets the engine's air/fuel mixture, such as a major vacuum leak, leaky EGR valve or unusually low fuel pressure (weak pump or faulty pressure regulator). There's really no magic bullet for finding misfires. It takes a certain amount of detective work to isolate the fault and determine the underlying cause. So, the next time you face a misfire, don't miss the mark

Last edited by Keith; 5th February 2007 at 14:17..
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Old 5th February 2007, 14:17   #15
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Default Intro to Emissions systems

When the first emission controls were first introduced back in the late 1960s, they were primarily "add-on" components that solved a particular emission need. When positive crankcase ventilation (PCV) became standard in 1968, the recycling of crankcase vapors eliminated blowby emissions as a major source of automotive pollution. When evaporative emission controls were added in 1971, charcoal canisters and sealed fuel systems eliminated fuel vapors as another factor that contributed to air pollution. Exhaust gas recirculation (EGR) was added in 1973, which lowered harmful oxides of nitrogen (NOX) emissions. But the most significant add-on came in 1975 when the auto makers were required to install catalytic converters on all new cars.
The catalytic converter proved to be a real breakthrough in controlling emissions because it reduced both unburned hydrocarbons (HC), a primary factor in the formation of urban smog, and carbon monoxide (CO), the most dangerous pollutant because it can be deadly even in small concentrations. The converter slashed the levels of these two pollutants nearly 90%!
The early "two-way" converters (so-called because they eliminated the two pollutants HC and CO) acted like an afterburner to reburn the pollutants in the exhaust. An air pump or an aspirator system provided the extra oxygen in the exhaust to get the job done. Two-way converters were used up until 1981 when three-way" converters were introduced. Three-way converters also reduced NOX concentrations in the exhaust, but required the addition of a computerized feedback fuel control system to do so.
Unlike the earlier two-way converters that could perform their job relatively efficiently with a lean fuel mixture, the catalyst inside a three-way converter that reduces NOX requires a rich fuel mixture. But a rich fuel mixture increases CO levels in the exhaust. So to reduce all three pollutants (HC, CO and NOX), a three-way converter requires a fuel mixture that constantly changes or flip flops back and forth from rich to lean. This, in turn, requires feedback carburetion or electronic fuel injection, plus an oxygen sensor in the exhaust to keep tabs on what’s happening with the fuel mixture.
Like the earlier two-way converters, three-way converters also require extra oxygen from an air pump or aspirator system, and some "three-way plus oxygen" converters are designed so air is routed right to the converter itself for more efficient operation.

Original equipment converters are designed for go 100,000 plus miles—which many do provided they aren’t poisoned by by lead, silicon or phosphorus. When leaded gasoline was still available, fuel switching to save money caused the premature demise of many a converter. Lead coats the catalyst rendering it useless. Silicon, which is used in antifreeze and certain types of RTV sealer, has the same effect. Coolant leaks in the combustion chamber can allow silicon to enter the exhaust and ruin the converter. Phosphorus, which is found in motor oil, can foul the converter is the engine is burning oil because of worn valve guides or rings.
Converters may also fail if they get too hot. This can be caused by unburned fuel in the exhaust. Contributing factors include a rich fuel mixture, ignition misfire (a fouled spark plug or bad plug wire) or a burned exhaust valve that leaks compression. Fuel in the exhaust has the same effect as dumping gasoline on a bed of glowing embers. Things get real hot real fast. If the converter’s temperature climbs high enough, it can melt the ceramic substrate that supports the catalyst causing a partial or complete blockage inside. This increases backpressure, preventing the engine from exhaling and robbing it of power. Fuel consumption may shoot up and the engine may feel sluggish at higher speeds. Or, if the converter is completely plugged, the engine may stall after starting and not restart.
There’s no way to rejuvenate a dead converter or to unclog or clean out a plugged converter, so replacement is the only repair option. Up to model year 1995, converters were covered by a 5 year/50,000 mile federal emissions warranty (7 years or 70,000 miles in California). In 1995, the warranty jumped to 8 years and 80,000 miles.
Replacement converters must be the same type as the original (two-way, three-way or three-way plus oxygen), EPA-approved and installed in the same location as the original.
A new converter will solve a plugged or dead converter problem. But unless the underlying cause is diagnosed and corrected, the replacement converter may suffer the same fate. Other items that should also be inspected include the air pump and related plumbing, oxygen sensor and feedback control system. A sluggish oxygen sensor, for example, may not allow the fuel mixture to change back and forth quickly enough to keep the converter working at peak efficiency. Though this might not lead to a meltdown, it could cause enough of an increase in pollution to make the vehicle fail and emissions test. If the oxygen sensor has died altogether, the fuel mixture will remain fixed and the engine will probably run too rich causing an increase in fuel consumption as well as emissions.
Many auto makers recommend inspecting the oxygen sensor at specific mileage intervals to prevent this kind of trouble. Some vehicles (primarily imports) have a reminder light that illuminates every 30,000 miles or so to remind the motorist to have his oxygen sensor checked or replaced.
A leading supplier of oxygen sensors (Bosch) recommends replacing oxygen sensors for preventative maintenance at roughly the same interval as the spark plugs, depending on the application. Unheated 1 or 2 wire wire O2 sensors on 1976 through early 1990s applications should be replaced every 30,000 to 50,000 miles. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications should be changed every 60,000 miles. And on 1996 and newer OBD II equipped vehicles, the recommended replacement interval is 100,000 miles.

PCV valves are generally considered a maintenance item like spark plugs, and should be inspected and replaced periodically (typically every 50,000 miles). The PCV valve siphons blowby vapors from the crankcase into the intake manifold so the vapors don’t escape into the atmosphere. One of the beneficial effects of PCV, besides eliminating blowby emissions, is that it pulls moisture out of the crankcase to extend oil life. Moisture can form acids and sludge which can cause major engine damage. So if the PCV valve or hose plugs up, rapid moisture buildup and oil breakdown can result.

The EGR valve has no recommended replacement or inspection interval, but that doesn’t mean it won’t cause trouble. EGR reduces the formation of oxides of nitrogen by diluting the air/fuel mixture with exhaust. This lowers combustion temperatures to keep it under 2500 degree F so little NOX is formed (the higher the flame temperature, the higher the rate at which oxygen and nitrogen react to form NOX). As an added benefit, EGR also helps prevent detonation.
The heart of the system is the EGR valve. The valve opens a small passage between the intake and exhaust manifolds. When ported vacuum is applied to the EGR valve diaphragm, it opens the valve allowing intake vacuum to siphon exhaust into the intake manifold. This has a same effect as a vacuum leak, so EGR is only used when the engine is warm and running above idle speed.
Some vehicles have "positive backpressure" EGR valves while others have "negative backpressure" EGR valves. Both types rely on exhaust system backpressure to open the valve. But the two types are not interchangeable. The vacuum control plumbing to the EGR valve usually includes a temperature vacuum switch (TVS) or solenoid to block or bleed vacuum until the engine warms up. On newer vehicles with computerized engine controls, the computer usually regulates the solenoid to further modify the opening of the EGR valve. Some vehicles even have an EGR valve that is driven by a small electric motor rather than being vacuum-actuated for even more precise control of this emission function.
EGR valves do not normally require maintenance, but can become clogged with carbon deposits that cause the valve to stick or prevent it from opening or closing properly. An EGR valve that’s stuck open will act like a vacuum leak and cause a rough idle and stalling. An EGR valve that has failed, refuses to open (or the EGR passageway i the manifold is clogged) will allow elevated NOX emissions and may also cause a detonation (spark knock) problem. Dirty EGR valves can sometimes be cleaned, but if the valve itself is defective it must be replaced.

On older carbureted engines, one of several emission control devices may be used to reduce emissions during warm-up. Fuel vaporizes slowly when it is cold, so heating the air before it enters the carburetor or throttle body improved fuel vaporization and allows the engine to more easily maintain a balanced air/fuel mixture. Most such engines have a "heated air intake" system that draws warm air from a "stove" around the exhaust manifold into the air cleaner.
A thermostat inside the air cleaner controls vacuum to a valve in the air cleaner inlet. When the engine is cold, the thermostat passes vacuum to the control valve, which closes a flap to outside air allowing heated air to be drawn into the air cleaner. As the engine warms up, the thermostat begins to bleed air, allowing the control door to open to outside air. Thus the thermostat and airflow control door are able to maintain a more consistent incoming air temperature.
One part that’s often needed here is the flexible tubing that connects the air cleaner to the exhaust stove. If damaged or missing, the engine may hesitate and stumble when cold.
Another early fuel evaporation aid on older V6 and V8 engines is a "heat riser valve." The valve is located on one exhaust manifold. When the engine is cold, the valve closes to blocks the flow of exhaust so it will be forced back through a crossover passage in the intake manifold directly under the carburetor. The hot exhaust heats the manifold to speed fuel vaporization and engine warm-up. Once the engine warms up, the heat riser valve opens. The heat riser valve needs to be replaced if it is sticking or inoperative.
On some engines, an electrically-heated "EFE grid" is used under the carburetor or throttle body to aid fuel vaporization when the engine is cold. A timer turns the grid off after a fixed period of time. If the grid fails to heat (bad relay, electrical connection, etc.), the engine may hesitate and stumble when cold.

Evaporative emissions from the fuel system (fuel vapors) are trapped and store in a charcoal canister. Later, a purge valve opens allowing the vapors to be sucked into the engine and reburned. The EVAP system usually requires no maintenance. The fuel filler cap is also part of the EVAP system, and is designed to keep fuel vapors from escaping into the atmosphere. A leaky or missing fuel filler cap may cause a vehicle to fail an emissions test.

Starting as early as 1994, some U.S. vehicles were equipped with a new government mandated onboard diagnostic (OBD II) system. By model year, 1996, OBD II was required on all new cars and light trucks.
OBD II is designed to detect emission problems. When a problem is detected, the Check Engine light comes on and a diagnostic trouble code is stored in the vehicle’s powertrain computer. Later, the code can be read using a scan tool to determine the nature of the problem.
With OBD II, the Check Engine light will come on anytime emissions exceed federal limits by 50% on two consecutive trips, or there’s a failure of a major emissions control system. With earlier engine control systems, the only way to uncover most emission problems is to give the vehicle an emissions test—which is not required in many rural areas. But OBD II is on every 1996 and newer car and light truck regardless of where it is registered in the U.S. And unlike an emissions test which may only be given once every year or two, OBD II is monitoring emissions performance every time the vehicle is driven.
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Old 5th February 2007, 14:21   #16
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Default Intro to engine management systems

The performance and emissions that today's engines deliver would be impossible without the electronics that manage everything from ignition and fuel delivery to every aspect of emissions control. Electronics make possible V8 engines that deliver excellent performance, good fuel economy and produce almost no pollution. But there's a price to be paid for today's technology, and that price is complexity.
Many powertrain control modules (PCMs) today have 16-bit and even 32-bit processors. Though not as powerful as the latest desktop personal computers, PCMs can still crunch a lot of information. It's been said that today's automotive PCMs have more computing power than the Space Shuttle's main processors. Kind of scary to think about, isn't it?
Does it take a rocket scientist to troubleshoot and repair drivability problems in today's cars? No, but it does take some knowledge, experience and diagnostic equipment that can access the onboard electronics.

From the outside, most PCMs look similar: just a metal box with some connectors on it. The PCM's job is to manage the powertrain. This includes the engine's ignition system, fuel injection system and emission controls. The PCM receives inputs from a wide variety of sensors and switches. Some of the more important ones will be discussed in the following paragraphs.

The oxygen sensor provides information about the fuel mixture. The PCM uses this to constantly re-adjust and fine tune the air/fuel ratio. This keeps emissions and fuel consumption to a minimum. A bad O2 sensor will typically make an engine run rich, use more fuel and pollute. O2 sensors deteriorate with age and may be contaminated if the engine burns oil or develops a coolant leak.
On 1996 and newer vehicles, there is also an additional O2 sensor behind the catalytic converter to monitor converter efficiency.
Though most O2 sensors have no recommended replacement interval (replace "as needed" only), sluggish O2 sensors can be replaced to restore like-new performance. Unheated one- or two-wire O2 sensors on 1976 through early 1990s applications can be replaced every 30,000 to 50,000 miles. Heated three- and four-wire O2 sensors on mid-1980s through mid-1990s applications can be changed every 60,000 miles. And on OBD II equipped vehicles, the sensor could be replaced once it has seen 100,000 miles.
The coolant sensor monitors engine temperature. The PCM uses this information to regulate a wide variety of ignition, fuel and emission control functions. When the engine is cold, for example, the fuel mixture needs to be richer to improve drivability. Once the engine reaches a certain temperature, the PCM starts using the signal from the O2 sensor to vary the fuel mixture. This is called "closed loop" operation, and it is necessary to keep emissions to a minimum.
The throttle position sensor (TPS) keeps the PCM informed about throttle position. The PCM uses this input to change spark timing and the fuel mixture as engine load changes. A problem here can cause a flat spot during acceleration (like a bad accelerator pump in a carburetor) as well as other drivability complaints.
The Airflow Sensor, of which there are several types, tells the PCM how much air the engine is drawing in as it runs. The PCM uses this to further vary the fuel mixture as needed. There are several types of airflow sensors including hot wire mass airflow sensors and the older flap-style vane airflow sensors. All are very expensive to replace.
Some engines do not have an airflow sensor and only estimate how much air the engine is actually taking in by monitoring engine rpm and using inputs from the throttle position sensor, a manifold absolute pressure sensor (MAP) and manifold air temperature (MAT) sensor. Problems with the airflow sensor can upset the fuel mixture and various drivability problems (hard starting, hesitation, stalling, rough idle, etc.)
The crankshaft position sensor serves the same function as the pickup assembly in an engine with a distributor. It does two things: It monitors engine rpm and helps the computer determine relative position of the crankshaft so the PCM can control spark timing and fuel delivery in the proper sequence. The PCM also uses the crank sensor's input to regulate idle speed, which it does by sending a signal to an idle speed control motor or idle air bypass motor. On some engines, an additional camshaft position sensor is used to provide additional input to the PCM about valve timing.
The manifold absolute pressure (MAP) sensor measures intake vacuum, which the PCM also uses to determine engine load. The MAP sensor's input affects ignition timing primarily, but also fuel delivery.
Knock sensors are used to detect vibrations produced by detonation. When the PCM receives a signal from the knock sensor, it momentarily retards timing while the engine is under load to protect the engine against spark knock.
The EGR position sensor tells the PCM when the exhaust gas recirculation (EGR) valve opens (and how much). This allows the PCM to detect problems with the EGR system that would increase pollution.
The vehicle speed sensor (VSS) keeps the PCM informed about how fast the vehicle is traveling. This is needed to control other functions such as torque converter lockup. The VSS signal is also used by other control modules, including the antilock brake system (ABS).
A couple of things to keep in mind when replacing sensors: Parts that are physically interchangeable may not be calibrated the same and won't work properly if installed in the wrong application. To make sure you get the correct replacement part, it may be necessary to refer to the vehicle VIN as well as OEM numbers on the original part. Some aftermarket parts may not look exactly the same as the original. A "universal" O2 sensor, for example, may fit a large number of applications but usually requires cutting and splicing wires to install.

On many vehicles the PCM also controls the transmission. But on some vehicles, a separate transmission control module (TCM) is used to oversee gear changes and the torque converter. But even if there's a separate module for the transmission, the PCM and TCM talk to each other and share data so each knows what the other is doing.
On many newer vehicles, the PCM also regulates charging system voltage; cycles the cooling fan on and off; interacts with the antilock brake system (ABS) module to reduce power if the vehicle has traction control; and may even interact with the automatic temperature control (ATC) module to operate the cycling of the air conditioning compressor clutch. The PCM may also be assigned vehicle security tasks.
One of the PCM's most important jobs is to make sure all the engine's sensors are working properly and that the engine isn't polluting. Since the earliest days of the onboard computer, a certain amount of self-diagnostic capability has always been required to detect problems that might upset the smooth operation of the system. On older vehicles, the diagnostics were relatively crude. If a sensor circuit went open (no signal) or shorted, the gross failure would set a trouble code and turn on the check engine light. But many conditions that didn't cause a total failure could also upset engine performance and drivability. What's more, the earlier systems had no way of monitoring many conditions that could increase pollution. So the Environmental Protection Agency (EPA) required every city and state that didn't meet Federal clean air standards to institute some type of vehicle emissions inspection program.

Emissions testing has certainly helped boost the sales of aftermarket PCMs, sensors and emission control parts. But more importantly, it has made a significant improvement in the air quality of most large metropolitan areas. Even so, many motorists will only seek repairs if forced to do so because their vehicle failed an emissions test. Many put off repairs until their vehicle is barely drivable or dies and leaves them stranded.
With computerized engine control systems, it doesn't take much of a sensor input problem to adversely affect drivability and emissions. A sluggish O2 sensor, a defective coolant sensor that always stays cold, a throttle position sensor that has a dead spot, an airflow sensor that isn't reading accurately, etc., can all hurt performance, fuel economy and emissions. In an attempt to ratchet up the self-diagnostic capability of PCMs, the California Air Resources Board developed a "next generation" onboard diagnostic system called OBD II. "OBD" is an acronym for "On Board Diagnostics." The "II" stands for "second-generation system." OBD II first appeared in 1994, and it has been required on all cars and light trucks since 1996.
Unlike earlier onboard diagnostic systems that set a diagnostic trouble code only when a sensor failed or read out of range, OBD II monitors most engine functions while the vehicle is being driven. It is designed to detect almost any problem that can cause emissions to exceed the federal limit by 1.5 times.
OBD II is extremely sensitive. Some say it is overly sensitive because the vehicle manufacturers have been overly cautious in setting trigger points below the 1.5 threshold to reduce the risk of expensive emission recalls. As a result, some vehicles may not actually have an emissions problem when the Check Engine light is on. Nevertheless, the problem should always be investigated to determine the cause.

The check engine light, which is technically called the "Malfunction Indicator Lamp" or MIL, is supposed to alert the driver when an emissions or sensor problem occurs. Depending on how the system is configured and the nature of the problem, the lamp may come on and go off, remain on continuously or flash - all of which can be very confusing because you have no way of knowing what the light means. Is it a serious problem or not?
For example, let's say a vehicle has an OBD II code for the oxygen sensor circuit (code P0130). The code might indicate a bad sensor, or it might indicate a loose connector or wiring problem.
Harder to diagnose are misfire codes. OBD II can detect misfires in individual cylinders as well as random misfires. If it generates a misfire code for a single cylinder (say P0301 for the #1 cylinder), it only tells you the cylinder is misfiring - not why. The underlying cause could be a bad spark plug, a bad plug wire, a weak coil on a distributorless ignition system (DIS) or coil-on-plug (COP) system, a dirty or dead fuel injector or a compression problem (bad valve, leaky head gasket, rounded cam lobe, etc.). As you can see, there are multiple possibilities, so it takes some diagnostic expertise to isolate the fault before any parts can be replaced.
A "random misfire code" (P0300) is even harder to diagnose because there can be numerous causes. A random misfire usually means the air/fuel mixture is running lean. But the cause might be anything from a hard-to-find vacuum leak to dirty injectors, low fuel pressure, a weak ignition coil, bad plug wires or compression problems.
Something else to keep in mind about OBD II fault codes is that some codes are false codes. GM has had problems with certain 3.8L engines setting P1406 codes, which indicates a fault in the EGR valve. Replacing the EGR valve doesn't fix the problem because the OBD II system is overly sensitive to how quickly the EGR valve opens when it is commanded to do so by the PCM. The cure here is not to replace the EGR valve but to "flash reprogram" the computer so it is less sensitive to this condition. Referring to vehicle manufacturer technical service bulletins (TSBs) can save a lot of time and frustration for these kinds of problems.
Something else that complicates diagnosis is that "standardized" OBD II codes really aren't. There are actually two different types. "Generic" OBD II codes are the same in the sense that all vehicle manufacturers use the same code numbers to indicate the same type of problem. But each vehicle manufacturer also has their own special "enhanced" codes that cover problems not included in the basic OBD II code list. These include many problems not covered by the generic codes as well as problems that are outside the engine management system such as ABS codes, climate control codes, body codes, air bag codes, etc.
Generic OBD II codes all start with "P0" while the OEM enhanced codes all start with a "P1." Enhanced codes are often vehicle specific and require a high-quality scan tool such as the AutoTap OBDII scantool for PC or Palm. Diagnosing computerized engine control systems and sensors isn't an easy task, but that's the price we pay for drastically reduced emissions and the feature-laden vehicles we drive today. So do your diagnostic homework before you replace critical engine management system parts. It will save you frustration and needless returns.

A couple of things to keep in mind when replacing sensors: Parts that are physically interchangeable may not be calibrated the same and won't work properly if installed in the wrong application. To make sure you get the correct replacement part, it may be necessary to refer to the vehicle VIN as well as OEM numbers on the original part. Some aftermarket parts may not look exactly the same as the original. A "universal" O2 sensor, for example, may fit a large number of applications but usually requires cutting and splicing wires to install.

Though most O2 sensors have no recommended replacement interval (replace "as needed" only), sluggish O2 sensors can be replaced to restore like-new performance. Unheated one- or two-wire O2 sensors on 1976 through early 1990s applications can be replaced every 30,000 to 50,000 miles. Heated three- and four-wire O2 sensors on mid-1980s through mid-1990s applications can be changed every 60,000 miles. And on OBD II equipped vehicles, the sensor could be replaced once it has seen 100,000 miles
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Old 8th February 2007, 14:45   #17
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Default Serpent wheels and centre Cap info

I have just been helping Simon sort out the right centre caps for his Serpents so might as well stick the info here as well for reference.

There are two versions of Serpent wheel one in satin silver as fitted to the facelift RRC110132MBS and one in sparkle? silver as fitted to the pre facelift cars RRC110131MNH.

Anyway whatever the colour there is an obvious visible difference in the finish and I think the facelift ones look slightly more metallic if compared side by side with the non facelift version.

The caps are also a slightly different colour and obviously have different logos and part numbers!

Serpents caps are
RRJ100110MBS new logo facelift
RRJ100110MNH old log pre facelift

I have the old logo style although the part number on mine like my wheels actually end in XXX i.e I have RRJ100110XXX caps!

Not sure what the XXX really means probably from a service line spare part number rather than a part number from the optional extra brochure where the above wheel and cap numbers come from

Last edited by Keith; 8th February 2007 at 14:49..
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Old 26th February 2007, 16:28   #18
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The chap at Texaco got back to me with further information:

Distributor contact details:

http://www.texaco-online.co.uk/ <http://www.texaco-online.co.uk/>

North East : James D. Johnson : 0191 5670002

Central and North West : Bates and Hunt Petroleum : 01743 718111

South West : OJ Williams : 01271 860953

South East : Team Flitwick : 01442 430402

Texco Customer Services : 01793 555702.

He also provided data sheets on ATF 402 and the manual gearbox oil MTF 94(hopefully attached)

I wonder, could we incorporate this information and the PDF data into the the automatic and manual gearbox oil change club data sheets? We have verbal permission to do so and i suggested that if we did I would get back in contact to allow Texaco final approval, out of courtesy.

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Old 4th March 2007, 18:04   #19
ROVER 75 2.5 V6 Connoisseur SE Limousine 2004

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Project Drive changes

Project Drive changes were implemented over a period of years and not in any obvious order as parts would only change or be deleted when stock of the original parts ran out. In 2001/2002 particularly, cars coming off the production line close to each other could be specced different in terms of Project Drive changes just because parts had run out!

Later in the production cycle (2004) the quality of leather used for seats was degraded along with other bits.

Project Drive began almost immediately production moved to Longbridge.

Rover 75 / MG ZT


Thanks to mike and Fille for this information.
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Old 11th March 2007, 18:58   #20
ROVER 75 2.5 V6 Connoisseur SE Limousine 2004

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Default Rover 75 and ZT Awards and Accolades 1999 - 2009

Rover 75 and ZT Awards and Accolades 1999 - 2009

• What Car? ‘Car of the Year’ 1999.
• What Car? ‘Compact Executive Car of the Year’ 1999
• What Car? ‘Diesel Car of the Year’ 1999
• Auto Express ’World Car’ 1999
• The Journal / AA ‘Business Car of the Year’ 1999
• Italian ‘World's Most Beautiful High Class Saloon’ 1999
• Bild am Sonntag ‘Golden Steering Wheel Award’ 1999
• The Society of Plastic Engineers ‘Innovative use of plastic’ 1999 for the 75's V6 plastic intake system.
• British International Motor Show ‘Best riding and handling front wheel drive saloon in the world’ 1999
• Japanese 'Import Car of the Year' 1999
• Japanese 'Import Car of the Year' 2000
• New Zealand's National Business Review 'Car of the Year' 2000
• Executive Class ‘Portuguese Car of the Year’ 2000
• What Car? ‘Compact Executive Car of the Year’ 2000
• The only executive car to be short-listed in the 2000 ‘European Car of the Year Awards’
• Used Car Buyer 'Used Car of the Year’ 2000
• Used Car Buyer ‘Used Car of the Year’ 2001
• Diesel Car Magazine ‘Compact Executive Car’ 2001
• JD Power customer satisfaction survey ‘Only European car in the Top 5’ 2001
• Auto Express Used Car Honours 'Best Diesel Car' 2002
• Used Car Buyer 'Best Used Medium Car’ 2002
• ITM ‘Car of the Year' 2002
• Used Car Buyer ‘Used Car of the Year’ 2004
• Used Car Buyer ‘Best Used Family Car of the Year’ 2004
• ‘Most popular British Forces Germany tax free car purchase’ 2004
• Auto Express Drive Power ‘Best Ride Quality’ 2006
• Rover 75 voted Best Family Saloon in AutoTrader Used Car Awards 2007
• MGZT 4th Auto Express Drive Power "Sports car" 2008
• MGZT winner Auto Express Drive Power "Sports car" 2009

Thanks to paranoid for pointing this out to us

Last edited by GreyGhost; 11th August 2009 at 22:07..
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