Hi everyone,

I have a 2002 XK8 4.2 that has been sat for about 6 years that has an issue with fuel pressure.

At idle (and when driving around gently) the fuel pressure is 55psi, however when accelerating harder it drops off a cliff (down to 11psi when at full throttle), causing the to car bog down/surge as a result.
I can nurse the car up to speed by depressing and releasing the throttle letting the pressure build up over time.

I've replaced the fuel filter however this had little to no affect. The old filter looks fine upon inspection.

Since this is a returnless fuel system I believe my next port of call would be the pump, or potentially a leak inside the tank after the pump? I do hear fuel dripping inside the tank when the car is running and I listen from the boot, however this may be normal?

I've attached a picture of the fuel pressure alongside throttle percentage to show how much it drops.
One thing to note, the engine is throwing an O2 sensor code (P1646), however it is my understanding this shouldnt have an effect on performance, only fuel efficiency?

A couple more things to note just in case they are relevant:
- I can smell fuel inside the cabin after driving, however there are no apparent fuel leaks anywhere.
- I monitored the MAF sensor readings while driving and they seem to be fine so doubt this is the cause.
- There are no codes other than the O2 code.

Any help or guideance is much appreciated!


Many thanks,
Ben

 

pump strainer is full of garbage from sitting so long. common problem

 

Thanks, this was the issue!

Was a bit fiddly getting the pump out but it was full of sludge. Cleaned it out, popped it back in and now back to normal.

Thanks!

 

You might want to consider a known good fuel injector cleaner next. That spike in pressure during throttle release is a sign that the pop valve at the pump is not releasing pressure. This is not major, but can lead to these annoying P0193 Pressure-too-high codes. Techron 3 seems to be able to work the pop valve into compliance for most of us.

As an aside, I consider your posting as yet another example of "these cars are meant to be driven". Nothing you didn't know already I am sure.

Best of luck, keep us posted.

 

^^ Yep, you have to drive these things regularly to keep them happy and healthy. Letting them sit for long periods of time invites all sorts of problems....