I have a 1997 XK8 coupe with an engine fault that has eluded me for a long time. The car drives impeccably but if I park it for around 30 minutes and then drive it again, after a couple of miles, it starts to misfire and the ENGINE FAULT amber warning displays. Often this is followed by a red warning - something like POOR PERFORMANCE and the car becomes almost undriveable. I then leave it a couple of hours to cool down and everything is cleared and it drives perfectly well again. If I stop for ten minutes or so then drive off, I don't get the problem. Or if I park for an hour or two, it's fine. But there is a window of something around 20 to 30 minutes which always causes the issue.


The car is otherwise in pristine condition, with 73,000 miles on the clock. I bought it about 12 years ago and it has had this problem all the time, which is why I have only put a thousand or so miles on it in all that time. I'd really like to drive it a lot more, but this frustrating fault means that regular use is simply not practical.


I did take the car to my local Jaguar dealer, but was told that they only look at Jaguars younger than 2010. I then took it to Advance Auto Parts to see if they could put a code reader on it, but they told me their reader only works if the check engine light is on - which it is not (not sure if it has one!). So I cannot offer any code clue. I really don't want to take the car to some random local shop where they will know nothing about XK8's.


I have delved extensively into this forum but have not been able to find a definitive clue as to the cause. I can't believe that this fault is unique to my car, so I am hoping someone here has experienced the same fault and can offer some guidance as to how to proceed.

 

That sounds very unusual. Do you know anyone with a decent code reader which you can take in the car and read the codes as soon as the warning message appears?

I suspect that if it were a gearbox issue it would say something to that effect on the dashboard so it's possibly something related to the heat of the engine. It's fine when hot and fine when cold but a middling temperature is causing the problem. What happens if you only drive for 5 minutes and then stop for 30 minutes? Does keeping the engine relatively cold like this mean that the fault never arises?

Richard

 

Hi Richard, yes it is fine when hot or cold, just doesn't like middling temp! It runs flawlessly for an hour or more - it just doesn't like being left to cool for 20 minutes or so!

I'll try to get a code reader on it.

 

Just to rule it out, I would invest in a fuel pressure test gauge. Attach the gauge cold, start the car and measure the pressure. Disconnect. Drive the car up to the "fault" temperature, reconnect and measure the pressure. Wait the prescribed amount of time and test the pressure before and after cranking.

I suspect you're going to find a fuel pump/fuel regulator fault. That's just a barely-educated guess.

I have access to five good scan tools, of assorted ages, from old to very new. None of them will work 100% on these finicky Jags. But, I can say with confidence that your Advanced Auto guy is full of sh*t. Even the most basic readers seem capable of reading the basic OBD codes from the Jag's ECU. It may only show misfires and fuel cutoff, or similar, which you already know.

 

97s all have ecms that are dying and need to be recapped, any attempt to diag is pissing in the wind before you take care of that. if it still has an original fuel pump that'll be on its deathbed too

 

I've been thinking about this "warm engine" problem since I last posted and I came to the same idea that a fuel pressure / regulation issue might well be the source of the problem. Obvious areas to investigate after the scan might be fuel filter and fuel pressure sensor / regulator / pump. The easiest to change, if it has never been changed, is probably the filter.

Richard

 

Unusual for a fault to persist for so long without apparently getting any worse.

There are many possibilities - some good ones are mentioned above.

However, the car has a system that is designed to report faults (what the car thinks is wrong). It may give you some clues.

Get the codes read before firing the parts cannon.

 

I second this!
WJ

 

There is no fuel pressure sensor on the 4.0 cars. So, you're stuck having to use a gauge. If you change the filter, don't forget new o-rings. I don't think any of the aftermarket filters come with them.