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Hi and a question :-D

I have an engine light come on, but only in one circumstance, heavy throttle at 1500 rpm or lower, it goes into limp mode and I get fault code P0191. I also get a cloud of white smoke( diesel, not water) for a second.

If I floor it at 1800 rpm plus then no problems, otherwise drives fine,

Any ideas from someone more knowledgeable than me?

I tried logging the fuel pressure vs desired pressure vs boost and I cant see a lot wrong, then again I dont know what it should be, all I can say is pressure is 300 at idle, tracks desired pressure mostly and peaks at about 1200 bar. Turbo peaks about 1 bar at 2500rpm.

I sometimes get a small lag in pressure during snap acceleration, but this may be due to logging frequency.

Thanks for any pointers, in case someone says ahh I know that problem.

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This code relates to fuel pressure, as you probably already know, and can be caused by a number of things;


The fuel pressure regulator or sensor (both attached to the the fuel rail) may be at fault either mechanically or electrically but the most likely cause is an irregular fuel supply. This can be caused by the lift pump in the tank malfunctioning or a blockage/air in the fuel filter. It could also be a problem with a sticking injector but we will leave that possibility alone for the moment because it is very rare on the 2.8JTD. The fact that it starts well is a good indication that there is not much wrong there. A leaking injector will prevent the fuel pressure from reaching the required 300bar in order to allow it to start without it being cranked for a long time.


I would first check for any leaks around the fuel filter and change the element if it has not been done for a while. I would check that the lift pump is running and timing out correctly: Switch ignition on and hear it running under the cab floor for about 20 seconds and stopping if the engine is not switched on. I should be a faint whirring sound and not too loud.


This sort of thing can take a bit of diagnosing because the light and code could be as a consequence of the engine going into limp mode because of something completely different and the smoke could also be as a result of the limp mode too, and there might be nothing at all wrong with the fuel supply!


Just do as many basic and cheap tests as you can and rule out something easy before getting an expert to look at it.

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Many thanks Euroserv, you are a mine of information on this: Yes I get lift pump whir on ignition, I would say it lasts for less than 20 seconds, also its an amazing starter always, it leaps into life in a split second, so your information on leaking injectors is interesting as it was a thought but it seems I can rule it out. The filter seems the next on the agenda, an easy fix I hope, thanks.


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