Hi all,

I have an ongoing problem that I hope someone may be able to help guide me to solving. Maybe someone may have experienced this before or may have some expertise on this as I know there are lots of knowledge on this forum that I greatly value. I have a 1998 xjr. The performance seem to have been lost compared to what it used to be. I will try my best to describe this problem.

-I noticed that when I floor the gas pedal from a stand still, the car doesn't not even peel out anymore and kind of just picks up sluggishly (I do have it on sports mode and have the traction control turned off). Throughout the rpm of 1st gear, I can feel the car cutting out and stuttering; and while looking at the rpm, I see it go through very slight but noticeable pauses and picking up again throughout. The rpm on first gear only goes up to about 5200 or so until it switches over to second gear. After a couple of punches, I start to smell fuel (although not overwhelmingly strong, the smell is very noticeable). This loss of power had been going on for quite sometime and I have tried many things with no luck. The car, however, drives fine and beautifully at regular driving. I can take a normal 300 mile trip with no problem whatsoever. There is no CEL so I really can't pinpoint what to check.

-Performance prior to this sudden loss of power: From a stand still in sports mode and traction control off, the car feels monsterous (I know monsterous is a bit of an exaggeration but these are awesome cars so what the heck) it will peel out first gear all the way and chirp on second gear with a slight peel out even after the shift to second gear. And it doesn't shift until it hits redline after 6000 rpm. No stutter and no fuel smell at all.

-some of the things I changed out hoping it would fix the problem are: fuel filter, changed the part load breather and cleaned the hole with the drill bit like some suggests here, full load breather, cleaned the MAF, checked the air intake pipe (no cracks whatsoever), cleaned the TB, changed spark plugs. The primary fuel pump did go out about 6 months ago and I changed out both primary and secondary pump (the loss of performance and not able to peel out from a stand still had started prior to the failing of the primary pump). I also know the traction control off/on works properly because I tried the whole brake and gas tire burn out with it on and off and it works properly. By the way, the chain tensioners are the metal ones. I don't know if that matters.

-the loss of power and not able to peel out like crazy from a stand still had been a while, but the stuttering, the shifting gear at 5000 rpm and the fuel smell I just noticed it.

Any help would be greatly appreciated. Thanks much in advance.

 

I didn't see that you checked that the butterfly is opening all the way, and a compression test would be a good idea, the nikasil may be eroded. Changing the transmission fluid and filter would be a good thing,also.

 

Could be a bad coil, would certainly check fuel pressure at wot (but don't do too many wots anymore, it’s dangerous for the engine now!). Check also the fuel trims at idle and different speeds, which may help in pinpointing a bad bad/clogged fuel injector.

 

I will check if he butterfly is opening all the way and the compression today and will update. Thanks

 

Sorry, but I am a newbie at all of this. How do I check the fuel pressure at WOT? Do I drive the car and attach the test meter while I smash the pedal down? Plus, if my scanner cannot read live fuel trim, what else can I do to determine if I have a bad/clogged fuel injector? Thanks much

 

If it runs smoothly the coils and injectors are not likely to be a problem. But it wouldn't be a bad idea to get some BG44K online and put that in the tank. I intend to do so myself before going on a trip next month.

The fuel smell could be due to a problem in the vapor recovery system. Use the search function to get some leads. A fuel rail leak is less likely, but worth checking.

And last, when was the fuel filter changed?

 

Yes, I thought about the BG 44 too. I will keep with the update. My local jag dealership is closed early today, but I will get it on Friday because they have it. Thanks very much for your help

 

There is a big difference between idle/low speed driving and wot (wide op throttle), both for the working of coils as the injectors.

So the engine can run smoothly at idle/low speed driving and also have bad full throttle performance (ie the sputtering) caused by injectors or coils (or something else...)

 

I would buy a simple code reader/live data reader, it can be invaluable. I like the ultragauge (for example), very handy, small, and can do all the needed things.

You need to elimintaie possibilities, so all this info is needed to understand what is possibly not working well. Fuel pressure would indeed be needed whislt having a meter attached, and do a full power run.

 

I had the same issue with my XK8. Take a look at the throttle adjustment thread below. It made a world of difference for mine.

https://www.jaguarforums.com/forum/x...estored-38663/

 

Basically you can guess / swap parts (gets costly) or look at what the computer sees via OBD (very cheap).

 

Had the same issue with my XJ8L, when I bought it 22 months ago:

- clean MAF, replace air filter -- fixed the majority of the problem.
- clean the throttle bore, carefully, and reinstall assuring airtightness.
- run a full can of fuel System cleaner through a tank of gas. BG 44, gum out ultra, SeaFoam
- took slack out of throttle cable.
- New iridium spark plugs.
- cleaned the breather tube with correct drill size (probably not needed on 01, but gets blocked on 98s).
- New fuel filter as a precaution.
-- assumes no oustanding OBD codes
-- Super charger issues and bad transmission separate problems I have not had to face.
-- assumes single fuel pump (na engine) working fine

 

Thanks guys for all the response. I've been out of town for the whole weekend since Christmas so I haven't had a chance be with the car and to work on it. I also am ordering the ultragauge reader as well so I will be getting some live data to update. Thanks again for all of you guys' help.

 

An update on what's going on. So I read the thread about the throttle cable and checked mine and found that it was a bit loose. I went ahead and turned it a few knots and now the car burns rubber again from a stand still. It did it on the both run that I tested. Thanks to all

However, the car still shifts at around 5000 rpm and there is still a slight smell of fuel after the 2 test run. I did not notice the slight bogging/stuttering, but it could be because I didn't take it far enough and just let off right after it shifts to second gear. Also, I didn't feel it stutter in first; possibly because it was peeling out the whole 1st gear until it shifted at around 5000 rpm.

I did not want to take it any further past 2nd to 3rd because I want to be safe with the engine as Andre (avos) had suggested; not to do many more WOT's. I am waiting to get the ultragauge to do more tests and along with the fuel pressure test then I will keep you guys with the updates. From there, base on what you all with experience suggest, I will then fix the problem and take it up further in gear. Again, thanks much for all your help

 

The fuel smell is a worry. I would eliminate the vapour system, as the computer does an integrity check on it. Maybe a leaky injector seal, or a damaged pipe underhood; which only becomes evident when second fuel pump kicks in. Maybe they broke something when changing the pump. As for coils, if they don't perform properly, the car will go into restricted performance mode.

 

So here's the latest update. Please correct me if I'm wrong, but I think the stuttering/hesitation comes from either a dirty strainer of the secondary fuel pump (since I did just change both pumps about 6-7 months ago) OR the secondary fuel pump is pretty much at its end.

What I did was I removed the relay for the primary pump and started the car up with it running only on the secondary pump. I tried to drive it around the block to see what's going on and felt the stuttering the moment I drove off. Before I even get half way around, the car stuttered and died with an "ENGINE STALL" message. Very similar to when my primary pump died about 6-7 months ago. What do you think? Does that test justify a bad secondary pump? Thanks much