Can anyone help? ‘04 facelift MG ZT T 2.5l KV6 Non Start.

[SD1too]

Originally Posted by P.happy.T

... we had a T4 man bring his diagnostics to the stricken car ...

Hello Paul,

Who was the T4 man? Was he one of the club members offering this service? Were any fault codes read? I'd have thought with your symptoms there must have been fault codes.

Simon

PS A while ago I recommended that you established that you have 3.5 bar of fuel pressure at the Schrader valve. Have you checked this?

[P.happy.T]

Hi Simon,
I didn't attend the T4 session unfortunately but Dan did & he says
"I don't recall much discussion of specific fault codes. It all seemed to be around the crank sensor not providing live data"
However we have had a go with TOAF today and the current codes are error P0264 and P0276 (Cylinder 2 and 6 injector circuit low) We believe that this would not stop the engine firing do you agree ? To get at the offending injector plugs which are next to the bulkhead the plenum will need to come off again.
I also rigged up a temporary set of 3 connections for the good K Series Cam Position Sensor, no success.
Strange that you mention fuel pressure I was thinking the same thing again, I got these readings this afternoon:-
Static Pressure with ignition on = 50 psi
Dynamic Pressure (Spinning the engine over on the key) = 50 psi
Resting Pressure after ignition key switched off = 30 psi
So I don't think there's anything wrong with the petrol delivery circuit.
Over to you with your wealth of experience !

Thanks,
Paul

[vitesse]

A V6 will start and run on only four cylinders. Initial fuel pressure readings look good, except for the resting pressure one - it’s been a while since I tested the fuel pressure but I’ve got an idea mine held over 3.5 bar even after the ignition was switched off, dropping very slowly until I got fed-up waiting and disconnected the fuel gauge with rags around it. I suppose it depends on the length of time of your resting pressure.

On the end of the fuel rail is a damper of some sort with a vacuum hose, never really understood its purpose but while the upper manifold is off it would be a good idea to examine the vacuum hose while inspecting the injector wiring.

Good luck

[P.happy.T]

The resting pressure dropped off to 30 psi as soon as we turned the ignition off so there could be a leak there however if the pressure is there when it's cranking it should still run shouldn't it ? I agree with you 4 out of 6 should be sufficient to get it running without easy start !
Also my pressure gauge is a basic metal tyre pressure gauge with the extending bar so in each test I release a bit of pressure which could explain the 30 psi figure.
Also in response to T4 codes taken about 6 weeks ago our man said
"T4 doesn’t give fault codes numbers unfortunately, only the faults. Only ones it came up with was the anti theft fault as toaf did and failed vis motors" We're not get the anti-theft fault anymore on TOAF.
Thanks,
Paul

[SD1too]

Originally Posted by P.happy.T

... we have had a go with TOAF today and the current codes are error P0264 and P0276 (Cylinder 2 and 6 injector circuit low) We believe that this would not stop the engine firing do you agree ?

I think that's an unwise assumption Paul. When my engine had a faulty ignition coil affecting only one cylinder, it wouldn't fire at all.

I know that getting access to the RH bank injectors is not something that any KV6 owner will rush to do but it's a mistake to try to convince yourself that those codes can be disregarded. There's a connector feeding the RH bank injectors and that would be the first thing I'd look at. Identify the yellow/brown wires (no. 2) and yellow/green (no. 6).

Simon

PS Whilst you're in there, reset the sparking plug gaps to the 1.0 mm book value if you haven't already done so.

[vitesse]

Just for the record, I not only experienced the irregular running V6 but it was confirmed by Rover54 during the remote T4 project that the engine ran on 5 but sometimes only 4 cylinders. However the fault was not the same as Simon’s but rather with the main ECU, your fault codes relate to the injectors rather than the coils so somewhat different too.

Another owner with P0276 found the injector wiring “chafed right through” - https://the75andztclub.co.uk/forum/s...t=20600&page=2

Good hunting

[Ducati750cc]

Originally Posted by Timefortea23

We tested a couple by removing the spark plug, plugging it into the coil pack and resting the threads of the plug against the block to earth it. Then cranked it and we got good spark.

An apparently good spark, at atmospheric pressure, in those conditions can be misleading, it doesn't need a great amount of energy for the current to jump the gap.

The spark to fire the mixture at TDC is under compression and the energy required is far greater.


Speaking generally of ignition system problems resulting in loss of spark in the cylinder, things like poor plug leads, poor coil pack to plug connectors, poor plugs, insulation breaking down and tracking in the plug apertures where it can't be seen, poor coils.

High resistance on the LT side side to the coil packs both on the + feed and on the switching circuit, incorrect dwell, either old points, or electronically ( that is the time taken for the coil to be switched on to off to create the HT) and so on.

There are a couple of ways to check that the KV value of the ignition HT side is within the norm the first and safest is using an oscilloscope which will not only show the peak, but the switching action, the second is crude, does work to a degree but is fraught with danger with modern systems and electronics and that is a gap tester.

This has an adjustable spark gap inside a transparent tube, at an air gap of around 15mm the HT will be around 20KV and would be sufficient to fire at compression pressure, however, if the gap is too wide, or the HT is too low to jump the gap, it has to go somewhere and it does like expensive electronics.

[Ducati750cc]

Originally Posted by P.happy.T

Hi Simon,
I didn't attend the T4 session unfortunately but Dan did & he says
"I don't recall much discussion of specific fault codes. It all seemed to be around the crank sensor not providing live data"
However we have had a go with TOAF today and the current codes are error P0264 and P0276 (Cylinder 2 and 6 injector circuit low) We believe that this would not stop the engine firing do you agree ? To get at the offending injector plugs which are next to the bulkhead the plenum will need to come off again.
I also rigged up a temporary set of 3 connections for the good K Series Cam Position Sensor, no success.
Strange that you mention fuel pressure I was thinking the same thing again, I got these readings this afternoon:-
Static Pressure with ignition on = 50 psi
Dynamic Pressure (Spinning the engine over on the key) = 50 psi
Resting Pressure after ignition key switched off = 30 psi
So I don't think there's anything wrong with the petrol delivery circuit.
Over to you with your wealth of experience !

Thanks,
Paul

You appear to be getting sufficient fuel pressure at the pump, are you getting the same at an injector/injectors and are they actually injecting ?



What do we need for successful combustion, air, a good spark at the right time, exceeding a minimum cranking speed and the correct quantity of fuel at the right time.


Presuming pump and rail pressure to be OK and there is fuel up to the injectors, then you have to look at if the injectors are 1) being switched and 2) how long for by the ECU, ( depending on variables, temp, throttle position engine position, info from from various sensors etc) the ECU will open the injectors for X milliseconds, to deliver the correct quantity of fuel, to put it simply it opens and closes a circuit to open an injector and that's it.


However the ECU doesn't know and has no way of knowing if any fuel has actually been injected, it could be air, until the engine fires and runs and the ECU gets info from the Lambda sensor etc.


So what are the injector fault codes you are seeing, which shouldn't be there at all, something is giving you a clue, it says ' circuit low ' meaning voltage low, this can be caused by a few things such as various faults with the injector, wiring / harness, multi-plugs, even the ECU.


If you are 100% sure, fuel pressure is OK, the first port of call is to check at the injector connectors that the correct voltages and switching pattern is OK, or even if they are switching at all, if voltages and pattern appear OK, suspect the injector/injectors, if incorrect voltages and pattern, or non at all, then multi plugs, loom back to the ECU needs to be checked and finally the injector pin outs at the ECU.


The fact that it fires on Easy start points to a fuelling problem, after prolonged cranking have you checked if there is a pronounced smell of petrol from the exhaust and / or signs of fuel on the plugs ?


If there were problems with say a couple of injectors or plugs, it should start and run on four, or at least attempt to do so which should be heard and seen.


A note of warning, if you do eventually get it to start and run, just let it run for a short while to warm up a bit, switch off, leave it for a short while and do the same again a couple of times, this is because after all your attempts and if fuel was being injected, it could have contaminated the cat which won't be too happy with the excess temps this can generate.

[P.happy.T]

Success, The ZT-T 190 runs again !
Thanks to everyone that offered patient advice over the last 3 months.
The final issue was that we found that the plug that feeds the 3 rear injectors had become detached when we changed the coolant pipes so what I thought was limp mode may have been 3 firing cylinders & a 3 cylinder compressor !
For me the lesson learnt is if you're trying to bring a stricken engine back to life give it a sniff of Easy Start before you start swapping out The ECU; Crank Sensors; TMAPS etc, you might save a lot of time & money !
Also TOAF has been a good thing for pointing us in the correct direction for diagnosis & for electrical faults you need more than a Haynes Manual.
Happy Days !
Paul

[Ducati750cc]

Originally Posted by P.happy.T

Success, The ZT-T 190 runs again !
Thanks to everyone that offered patient advice over the last 3 months.
The final issue was that we found that the plug that feeds the 3 rear injectors had become detached when we changed the coolant pipes so what I thought was limp mode may have been 3 firing cylinders & a 3 cylinder compressor !
For me the lesson learnt is if you're trying to bring a stricken engine back to life give it a sniff of Easy Start before you start swapping out The ECU; Crank Sensors; TMAPS etc, you might save a lot of time & money !
Also TOAF has been a good thing for pointing us in the correct direction for diagnosis & for electrical faults you need more than a Haynes Manual.
Happy Days !
Paul

Nice one and thanks for coming back with the results, it may help others.
It's amazing how such a simple thing like a disconnected/loose plug can be easily missed,especially with a 6 cylinder in a crowded engine bay.


One good thing has come out of it, is that you know a lot more about your car than you did 3 months ago, time now to get it out and enjoy it.