Hi

Some time back I noticed a judder when I accelerated hard. It felt like the engine wasn't getting enough fuel. One or two people I spoke to suggested it was the gearbox, this filled me with dread as I know the cost of replacement is almost as much as the car is worth and I seem to remember the XJR gearbox is a Mercedes unit and is considered pretty bullet proof. Anyway over time the problem has got worse. The car hesitates at lights then picks up. If I accelerate gently then the problems not as obvious. The good news, if indeed that's what it is, is that you can now feel it on tick over with the gearbox disengaged or if you rev the engine.
My suspicion is that it's injectors, coil packs or plugs. I have no visible fault indicators and nothings coming up on the diagnostic computer. Is there a fuel filter somewhere it could also be this but I'm not sure there is one.
Anyway I'm open to suggestions as I'm reluctant to shell out hard cash if it doesn't cure the problem.
Cheers
Ian

 

Most likely the second fuel pump has failed. There's many threads dealing with how to isolate the problem. Replace both so you don't have to go in there again.

 

Could also be your MAF sensor.
If the engine was actually misfiring you'd be getting warnings and codes. Much more likely to be fuel pressure or MAF related.
Does it only happen when you accelerate hard from a standstill, or when you're at speed too?

 

That sounds like what I had when I needed to replace some of my coils.

 

+1 on MAF I experienced similar issues when my MAF was gummed up.

 

Your fuel filter is behind the rear passenger wheel, bolted to the rear bulkhead. They do benefit from periodic change.
XJR have 2 fuel pumps, you can check fuel pressure at the injection rail, there's a valve a fuel pressure tester connects to.
Maf is located at the front of the induction tube, 2 screws has it out, blast the sensors with electric contact cleaner spray, and maybe a Q tip.
Coil failure usually posts a code....
How old are your plugs? they should have a 1mm gap.

 

Thanks for the info.
Yes it's mostly a problem when the engine is under load. Seems ok when cruising.
I'll take a look at the MAF first as it's the easiest to get to then look at the other options and let you know.
Thanks.