Had the XJR a couple of months now and slowly plowing through the issues. Tensioners done. Discs done. Next issue, finding the HP. First step was adjusting the throttle cable, and boy do you notice the difference between 85% and 100%.

However that's made it even more obvious what a big midrange hole there is. Mid throttle or more, at anything less than 4000rpm results in not much acceleration, and often some hesitation.

Over 4000 though it's OK. Passing through that rpm at full throttle is like a race engine coming on the cam. It's doing 0-60 in about 6.0, which given that the first bit takes forever seems to indicate that the top end's about where it should be.

Having had a look through Sinister 1's list at https://www.jaguarforums.com/forum/x...agnosis-52294/, and various other lack-of-power threads, I kinda suspect the EGR. Plus a quick look down the butterfly shows some coking where the EGR tube enters the throttle elbow. However my understanding is that EGR on most cars happens at part load only. So it should be shutting off at full throttle anyway, in which case a clogged one wouldn't affect full bore performance.

Any other ideas? What's supposed to switch on or off at 4000 rpm? I don't think it's the supercharger bypass - the charger whine is audible before 4000 rpm and doesn't change as it passes through there.

It's not throwing any codes.

Also, since I'll probably rip the EGR off & clean it up sooner or later just on principle, even if its not the guilty party here: any steers on taking throttle body and elbow off first, versus just pulling the valve off from the back? JTIS doesn't call up pulling the throttle body to remove the EGR, but when the process is mentioned in the forum, most people seem to take off the whole mess. On the one hand, access looks ugly without the throttle body off, on the other hand, I prefer not to disconnect electrical plugs on old cars if I can avoid it: saves on gremlins later. Any good reason to do it one way or the other?

Thanks,
Dave

 

The second fuel pump is supposed to kick in at about 3400 rpm.

 

After any number of blind alleys and misdiagnosis (by myself and so-called experts), it turned out to be a combination of dirty MAF and defective EGR. What's doubly frustrating is that these are obvious issues and I'd looked at both parts right at the start of the saga. The smoking gun in the end was very -ve LTFT at low loads & revs: there's only so many things that can be.

Lessons learned:
* just because a MAF looks clean and you've cleaned it according to the instructions on the can, doesn't mean its actually clean
* just because an EGR is clean and not throwing codes doesn't mean it's working properly.

Still, on the upside, pretty much everything under the hood that can be fettled has been, it didn't cost me an awful lot except time and irritation, and it now runs just like a bought one

 

What was wrong with the EGR valve ? What did you do to clean the MAF?
thanks

 

MAF I just repeated the original procedure: squirt some MAF cleaner over the wires 10 or 15 times. It was pretty much an "its easy enough to do so I might as well give it another try before replacing the thing" job. Guess there must have been something on there which was too thick or sticky for the first cleanup to take it right off. The wires looked nice and shiny even before the first clean though. That gave me my midrange back, but didn't fix the -ve LTFT problem.

The EGR I don't know what was wrong with it, I just know that a new one fixed it: bottom end torque's back where it should be and the trims are within reason (bank 1 -1%, bank 2 -5%, +/-1% or so depending on load).

The old EGR looked fine after the original cleaning: valve was seating nicely and the spring loading seemed OK. I guess maybe the actuator didn't have full torque or something - if it wasn't doing anything at all, I'd have thought it should have been coding. The new one does sound a bit different - at least there's a servo-ish noise from that general area that I don't remember before. Or rather, I'm hoping that's the new EGR - the other alternative is that my throttle body's getting noisy, which wouldn't be good.

 

I think the XJR is like the XKR - there's a 'letter box' in the air filter box that opens when you put your foot down. Mine was stuck open and so the car was running on warm air from under the bonnet.
Getting that working actually improved low end performance
No-one ever mentions this.
Except me !

 

Steve - my car does not have the letter box flap in the air cleaner. I don't think any of the X308 cars have them