I've had my 03 XKR conv for about a year now and have put a couple 1000 miles on it and it has run perfectly, smooth, quiet... shifts smoothly, perfectly, in j-gate or auto... pulls very hard, supercharger whines... no engine lights on.
And I drive it pretty hard - I only take it out for fun and while I don't beat on it, I certainly wring it out frequently.

The exception to all this is that 3 or 4 times now over that entire span, under hard acceleration, at mid RPM (not hitting rev limiter), it hits a hard stumble or cut. It's a very short/sharp cut that reminds me of an old 92' Eagle talon turbo car I modified the heck out of and when you over ran the stock MAF (or maybe injectors - I can't recall specifically) the ECU would intentionally cut fuel to protect the engine, and it would be a very vigorous *bang* almost like you drove over a baseball bat in the road.

This stumble is not ~quite~ as aggressive but it is a very significant jolt, which hits nearly instantaneously - one jolt and gone, and I have literally never even encountered even the slightest unevenness in the car at idle or on a rip other than these few distinct events.... it's beautiful otherwise - no hesitation, roughness, etc, ever.

I don't think this is a misfire, and I don't have any such codes.... misfires being much more subtle to my understanding, and seems like one cylinder wouldn't be that aggressive of a hit.

Anyone run into this or have any ideas? I can't get it to repeat it specifically to test, but it just happened today on a big uphill sweeper under WOT between 4-5krpm.

Car seem no worse for the event - and is back to running perfectly immediately after the fact - but something both of us would like to avoid experiencing again I'm sure!

 

Maybe the 2nd fuel pump?

 

2003 was year Jag changed engine management to PWM vs return fuel system. Only 1 pump. Maybe fuel filter need changed?

 

I expected the R to have 2 pumps as mine has.

 

AFAIK, all the 4.2 cars have just one pump. For some reason, the 4.2 fuel pump is quite pricey compared to the 4.0 pumps, according to what I’ve read here.

PS: I’m at 201,000 miles on my 2002 XKR and still on both of the original pumps (thank goodness)



Z

 

That is because you drive your car on a regular basis so your fuel pumps do not get the chance to sit around and die. Good for you....

 

it is amazing that the most productive maintenance for these cars is to simply drive them more often.

Yet people don’t.

 

This one's got 53k so could be a victim. I wonder if the OBD logging would be sensitive enough to detect this - what would effectively be a drop in fuel pressure if the pump is failing. I don't mind swapping out a filter but would be hesitant to swap an expensive pump on a 99.9% rare occurrence I cant really even repeat at will. I think I will swap out the filter just as part of general maintenance after all these years anyway - then just keep fingers crossed and see what happens.

 

On the 4.2 you can read the fuel pressure, but you would have to have your reader (whichever one you are using) permanently running and logging the data on the off chance you catch it going wrong. Given what you have said I don't think that's feasible with such an intermittent fault.

Does anything show on the message centre on the dashboard when it happens? Could it be the traction control very briefly kicking in?

 

Yeah it seems unlikely to catch it in the act - but I should be able to at least log some of those values under a hard pull and see if they are close to limits or anything erratic happening at all.
So far nothing on the dash... and I've had TSC turned off in all cases it's happened - plus it feels much more emphatic than the TSC does - although my TSC experience has always been at low speed off the line, so wouldn't rule it out entirely.
I do need to check the 'pending' codes - it's still possible there's something there and it goes away since it doesn't happen often.

 

Definitely worth recording some data - fuel pressure, fuel trims, MAF etc. There are no misfire counters on the 4.0 cars sadly, worth having a look to see if they added it to the 4.2.