Citroen XM Forum

Hi Matthew

Check the fuel lines for kinks.
Rubber pipe kinks can cause fuel starvation as demand increases.
Check the tank pump housing base to be sure the three spacer pips have not worn away.
With worn away pips then suction at heavy demand can pick up the plastic base of the fuel tank.
This heavily restricts fuel supply.

John

I am fairly convinced its electrical but thats just a hunch based on the looking at your video of the Tach.

If it were me, to rule out fuel while it still at least starts i would pop the intake off to reveal the throttle body, start the engine and fill a small container with petrol (WD40 lid or egg cup) dont pour from a bigger container as if it is fuel related it may well spit back after performing this test and you dont want the sort of hair cut 5ltrs of burning petrol will give you.
Open the throttle manually fully and if the engine runs as described it will sit at about 2000rpm, then pour the fuel directly into the intake, if the engine is starved of fuel it should rev up possibly to the red line before leaning back out and farting and popping back to 2k.
This would prove poor fuel delivery in either volume or pressure.
IF it does nothing at all then you must be looking at the electrical system, either engine management or HT ignition or a mechanical problem such as bad timing.

Do you have a lexia Matthew, it would be most helpfull to see the live data output from the ecu with ignition advance, throttle position, engine speed etc, the clues will be there as to why its unhappy im sure.

D

Thanks John and I have thoroughly checked the fuel lines in the engine bay where disturbed and also tried two other pumps with no change. I also blew out the flow and return pipes between the pump and engine in both directions to ensure there was no obstruction. With regards, Matthew T.

I am also grateful for your suggestion Will and I will give it a shot later when I make the further video and let you know what happens! Unfortunately I do not have a Lexia, but there is Dave-the-Rave locally with one who I am sure would oblige and that is another good thought! With regards, Matthew T.

Well chaps it is definitely a fuelling (or lack of) issue, established thanks to Wills handy top tip!

https://www.youtube.com/watch?v=Njpw82J ... e=youtu.be" onclick="window.open(this.href);return false;

I needed a bit of practice and also my daughter to operate the phone but all worked well.

Just to confirm the relevant items that I have checked and changed to date:

- Fuel filter, pump and pipes
- Relays for fuel pump and oxygen sensor and associated wiring
- Ecu and sensors for water, air manifold temp etc. and wiring

I still need to find the cause, but at least that rules out a few possibilities!

With regards,

Matthew T.

It was Dean suggested the cup of fuel, which is something I have done on many occasions as a test.

I know you have changed the fuel pump, but is the +12v supply and equally as importantly, the -ve return good. I know of a case where the -ve return was poor causing bad running issues.

Try either measuring the fuel pressure under load or using a separate container of fuel and another pump connected straight to a 12v supply directly to the fuel rail. One other thing that could reduce fuel pressure is the regulator on the rail.

Mixture strength will be controlled by the Lambda sensor and MAP sensor, but I doubt it's that, as it is too extreme.

I am sorry Dean for that mistake and thank YOU for the suggestion! In response to your further thoughts Will, I shall check the electrical connections on the pump and perhaps try another known good example from a different car. I can confirm that I have replaced the regulator and lambda and MAP sensors with no effect! The car was very low on fuel when it last came off the road and jacked up at the front for a while with the petrol pipes disconnected, but I do not suppose that is significant? Regards, Matthew T.

Dramatic confirmation of a fuelling issue - and that sounded good!
One step forward!

When you reconnected the pipes...I trust they were the correct way round? Are you pushing fuel through the pressure regulator at idle, but as demand increases and the regulator shuts there is no fuel flow?

Thanks Chris and Will and just to confirm that the fuel pipes cannot be wrongly connected physically as they are shaped across the top of the engine. I wonder if anyone has a diagram of the fuel pump wiring that is one of my next ports of call? In relation to the fuel system, I guess the issue must either 'mechanical' or electronic in something not operating correctly like a broken pump or duff sensor, or electrical through a wiring fault. The bottom line is that the engine is not getting enough fuel to rev, either because of the lack of fuel being supplied, or through being told it does not need fuel when it does! I hope that makes sense! Regards, Matthew T.