Intank Fuel Pumps

[suffolk boy]

while i not saying you are wrong my intank pump failed rapidly followed by the ub pump which gave up under the strain in fact under 1/4 tank and it would not start anyway no running on mkon pumps with no problems if it was only acting as a transfer pump and can done away with as you have done i am sure rover would come up with it the 1st place if to save money only

[COLVERT]

Originally Posted by T-Cut

That wouldn't explain why many diesels with a failed in-tank pump won't start/run even when the tank is full. The under-bonnet pump in the early system cannot lift fuel efficiently from the tank to bonnet level. It has to be primed by the other pump. Later systems use a stronger lift pump u/b and dispense with the one in the tank. Your modification may not last as long as you hope since the paired pumps usually fail after a similar period. Does it lift OK when the tank's getting very low?

TC

Well T-Cut as you say "the Troof is out there" but we don't seem to have found it in this thread !!
Front pump gone???: rear pump gone ???

Function of rear pump: function of front pump.

The plot thickens. Lol.

Colvert. ( T.S.Autos, where are you ?? )

[ade75]

Just an update on my "deletion of intake pump" which caused quite a few varied opinions back in January. 5 months later I have now covered 6.5K miles with no issues whatsoever, engine runs fine and only needs underbonnet pump to supply fuel.

[Mike Noc]

Originally Posted by ade75

Intank pump is not part of the fuel delivery system, it merely keeps the fuel leveloft both chambers of the tank at an even level, therefore preventing fuel starvation to the ub pump.

Ade can I ask how have you have come to that conclusion? Have you run the ITP on its own and found no fuel supplied to the UBP inlet?

As far as I know the system is designed so that the ITP supplies fuel to the UBP and also equalises the tank levels each side of the saddle.

When the ITP fails the car will still run as long as the tank isn't allowed to get too low, as if it does I think the remaining fuel is on the wrong side of the saddle and then the UBP sucks air.

It could be that some owners are unaware of ITP failure and then when their UBP fails they find both pumps gone and assume they failed together.

I also think that with a failed ITP you are putting more strain on the UBP so it will wear out more quickly, but to put that into perspective my UBP ran for 20,000 miles on its own after the ITP failed and was still going strong when both were replaced.

Agree with Colvert we don't have a definitive answer to exactly how the system works but hopefully the more it is discussed the clearer it will become.

Mike

[T-Cut]

I did some reading on the diesel pumping system (which is more or less the same in petrol models) and it's clear from this, that there are several misunderstandings about how it works. The low pressure diesel pumps do not circulate fuel across the tank. They simply deliver fuel to the injector pump. The high pressure backflow from the high pressure pump and injectors is what motivates tank levelling. Here's what the book says:

Diesel Fuel Delivery

The fuel tank is of saddle design, with a central hump and two deep sections each side. A submersible electric pump is located in the right hand section. This pump is called the primary low pressure pump (PLPP).

The PLPP draws fuel from a swirl pot beneath and delivers it to a filter unit adapter (FUA) mounted in the left hand section. Apart from a filter element, the FUA contains a fuel pressure regulator which is calibrated to 3.6 bar (52 psi). This regulator is not open during normal operation of the system.

Fuel leaves the tank from an outlet on the top of the FUA and is transferred to a secondary low pressure pump (SLPP) mounted under the bonnet near the battery tray. Both the PLPP and the SLPP are controlled by the ECM via a single relay located in the passenger side interior fuse board. When the ignition is switched on, the relay is
energised for up to 20 seconds. This activates the two pumps to build up about 2.5 bar (36psi) fuel pressure to the main fuel filter (under bonnet) and the high pressure pump (HPP).

The spill return from the HPP and the fuel injectors is returned via an external cooler and through a connection to the right hand section of the tank. The HP flow is divided into two streams by a T-piece connection. Each stream passes fuel through a venturi type static pump. One venturi draws fuel from the left side of the tank and delivers it to the right side. The other stream passes fuel through the second venturi which draws fuel from the right side of the tank and delivers it into the swirl pot surrounding the PLPP inlet. This arrangement ensures that the left side of the tank is scavenged into the right hand side and the fuel level in the swirl pot is constantly maintained regardless of vehicle movement.

Each side of the tank contains a float controlled sender unit to detect fuel levels. The senders are connected in series to the IPK. The IPK uses an algorithm to intergrate each sender signal to determine overall fuel content.

The ECM detects the fuel pressure in the LP side of the system using a sensor mounted in the fuel head. The sensor output is required by the ECM to determine if the HPP is receiving sufficient pressure. If the ECM detects insufficient inlet pressure, it will reduce engine speed and fuel rail pressure accordingly to prevent damage to the HPP.

The fuel pump relay is a 4-pin, normally open type. The ECM controls the ground path to the relay solenoid. When activated, the relay supplies power to both PLPP and SLPP. When the ignition is switched on, the pumps raise fuel pressure to 2.5bar (36psi). The ECM then deactivates the relay after about 60 seconds. If the ignition is
turned on and the engine is started, the ECM energises the relay continuously. The input supply to the relay solenoid is battery voltage, the ground path for the winding is from the ECM driver circuit. The input supply for the switching contacts comes from the engine compartment fuse box. The output from the contacts is directed to the PLPP and the SLPP motors.

In the event of a fuel pump relay failure, any of the following symptoms may occur:
The engine won't start
No fuel pressure at the fuel rail

NOTE: Later models only have the PLPP in the tank. Other than that, the system operates as described above.

[RoryRover]

I have a 2004 Connie SE CDTi Tourer - will it have an underbonet pump or just the in tank unit ?

[Hengist]

Interesting thread!

John - open bonnet, find battery, look to the left of it. Beside the front of the battery is your fuel filter. Beside the back of the battery is your under-bonnet pump - if it exists.

Angus

[Mike Noc]

Originally Posted by T-Cut

I did some reading on the diesel pumping system (which is more or less the same in petrol models) and it's clear from this, that there are several misunderstandings about how it works. The low pressure diesel pumps do not circulate fuel across the tank. They simply deliver fuel to the injector pump. The high pressure backflow from the high pressure pump and injectors is what motivates tank levelling. Here's what the book says:

Diesel Fuel Delivery

The fuel tank is of saddle design, with a central hump and two deep sections each side. A submersible electric pump is located in the right hand section. This pump is called the primary low pressure pump (PLPP).

The PLPP draws fuel from a swirl pot beneath and delivers it to a filter unit adapter (FUA) mounted in the left hand section. Apart from a filter element, the FUA contains a fuel pressure regulator which is calibrated to 3.6 bar (52 psi). This regulator is not open during normal operation of the system.

Fuel leaves the tank from an outlet on the top of the FUA and is transferred to a secondary low pressure pump (SLPP) mounted under the bonnet near the battery tray. Both the PLPP and the SLPP are controlled by the ECM via a single relay located in the passenger side interior fuse board. When the ignition is switched on, the relay is
energised for up to 20 seconds. This activates the two pumps to build up about 2.5 bar (36psi) fuel pressure to the main fuel filter (under bonnet) and the high pressure pump (HPP).

The spill return from the HPP and the fuel injectors is returned via an external cooler and through a connection to the right hand section of the tank. The HP flow is divided into two streams by a T-piece connection. Each stream passes fuel through a venturi type static pump. One venturi draws fuel from the left side of the tank and delivers it to the right side. The other stream passes fuel through the second venturi which draws fuel from the right side of the tank and delivers it into the swirl pot surrounding the PLPP inlet. This arrangement ensures that the left side of the tank is scavenged into the right hand side and the fuel level in the swirl pot is constantly maintained regardless of vehicle movement.

Each side of the tank contains a float controlled sender unit to detect fuel levels. The senders are connected in series to the IPK. The IPK uses an algorithm to intergrate each sender signal to determine overall fuel content.

The ECM detects the fuel pressure in the LP side of the system using a sensor mounted in the fuel head. The sensor output is required by the ECM to determine if the HPP is receiving sufficient pressure. If the ECM detects insufficient inlet pressure, it will reduce engine speed and fuel rail pressure accordingly to prevent damage to the HPP.

The fuel pump relay is a 4-pin, normally open type. The ECM controls the ground path to the relay solenoid. When activated, the relay supplies power to both PLPP and SLPP. When the ignition is switched on, the pumps raise fuel pressure to 2.5bar (36psi). The ECM then deactivates the relay after about 60 seconds. If the ignition is
turned on and the engine is started, the ECM energises the relay continuously. The input supply to the relay solenoid is battery voltage, the ground path for the winding is from the ECM driver circuit. The input supply for the switching contacts comes from the engine compartment fuse box. The output from the contacts is directed to the PLPP and the SLPP motors.

In the event of a fuel pump relay failure, any of the following symptoms may occur:
The engine won't start
No fuel pressure at the fuel rail

NOTE: Later models only have the PLPP in the tank. Other than that, the system operates as described above.

Hi TC, as far as I know there is no intank fuel filter on the diesel models which is why the unit is called a Filter Unit Adapter, as it sits where the filter would be in the petrol models.

Also the ITP, which draws fuel from the right hand side does indeed equalise levels in the tank via the appropriately named scavenge pipe going from the left hand side back to the right.

Mike

[T-Cut]

The book refers to the under-bonnet filter as the 'main' fuel filter, which rather suggests the tank module has some filtration capacity. Why would it be called a 'filter unit adapter' if there's no filter involved. I don't go for the comparison with the petrol module to describe the diesel module. I don't know for sure whether there is or not, but would it not be called the 'transfer adapter' or something similar? It really needs someone to take a close look inside the gizmo to be sure.

The book doesn't mention the ITP delivering fuel to the left side. The description of operation is almost verbatim from the MGR text. I'd have thought the fuel delivered by the ITP is all needed to feed the ubp and through that, the HPP. However, no further mention is made of the function of the pressure regulator in the left side adapter. I assume this relieves any pressure above 52psi generated by the ITP if there's a blockage upstream. I guess that could be discharged back to the rhs tank, but that's only conjecture.

Basically, the MGR documents make no mention of fuel equilibration by the ITP. It's described as entirely via HP backflow through the two venturis.

There's also a flow diagram of the tank, but it's pretty small scale and leaves you vague as to how fuel might flow from the ITP to the left module and back into the rhs tank. I can't post it here for copyright reasons.

TC

[COLVERT]

Originally Posted by ade75

Just an update on my "deletion of intake pump" which caused quite a few varied opinions back in January. 5 months later I have now covered 6.5K miles with no issues whatsoever, engine runs fine and only needs underbonnet pump to supply fuel.

Very strange !!! So how is fuel transferred from one side of the fuel tank to the other without a pump ???




Colvert. ( ie. Saddle tank. )