Hello,

Ive been having a hard time figuring out this problem. When the car is cold the car runs fine, however starts to run rough as the engine starts to warm up. I have in fact done a good amount of research on the matter.

So far i have:
Changed the spark plug twice
Changed the coil to a new coil twice, there was a small amount of oil on the coil, but shouldnt have been enough to foul the coil. And after replacing it with a new one the code came back nearly right away.
The injector for that cylinder was changed 6 months ago and when using a stethescope seems fine

I have not performed a compession check yet, just afraid of the results, i cant afford to pull apart the whole engine. However i am going to perform one tomorrow. The engine has 117K miles, and i would imagine the rings should last much longer than that.

I want to swap the ignition modules, however i do not know where they are located? I was hoping someone could give me some insight.

Any other thoughts would be greatly appreciated.

Thanks in advance
Adam

 

it might pay to add 04 STR to your signature .

i think the module is the ECM and the igniters are in the coils . i wonder if there might be a broken wire in the coil loom .

i think though as it heats then fails ill bet you have valve recession . and may just need the valves in cylinder 8 re shimmed

 

Maybe you have mis-identified where #8 is?

Or might be wiring.

Possibly, though rarely, the PCM has been / is wet.

Working through the list of causes in the workshop manual is probably best.

 

I really wished that was the case. I have looked at the diagram a few times now. Cylinder 8 is drivers side closest to the firewall.

wiring is a possablitly. I have checked the exposed wires once it leaves the loom and the seem fine. However i pulled the supercharger over the summer to change the injector, and its possible i messed it up during install.

Where is the PCM located? I can check for any kind possible water damage.

Something has come up and wont be doing compressions today. More than likely ealry this week though, i have enough problems with the car that its not my DD anymore.

 

I would like to do as much as possible without bringing it in, if the valves needed to be reshimmed i dont think its something i would attempt myself.

 

Why was the injector changed? Was it for this problem, or for some other reason?

You mentioned having twice changed the spark plug and coil. With a cylinder-specific fault, it's generally more conclusive (and cheaper!) to swap in known good components from another cylinder for troubleshooting. Move the suspect components to other locations and see if the fault follows or stays put.

I mention this because I've had several new parts turn out to be defective. Not super common, but it happens. One time I even returned a defective part only to get another bad one from the same defective lot. Talk about a headscratcher! The fix was getting a third replacement (different brand) from another store.

Once again, it's highly unlikely you've purchased two bad coils or two bad spark plugs, but do keep that on the back burner if all other troubleshooting comes up empty.

Back to that injector, even if it sounds normal, it could still be clogged. I'd suggest swapping that with a known-good injector from another cylinder and seeing if the fault follows or stays put.

It wouldn't hurt to swap the coil with a known-good one while you're at it. Just pick a different cylinder than the injector swap so you'd know which component was at fault if it moves.

After that it's time for a compression test. As others have mentioned, a valve problem is more likely than leaking rings. The fix could be a simple adjustment.

 

Sorry, i should have mentioned i tried swapping coils first, but i came across a thread earlier where someone was also having the same problem, and he was swapping coils as well. Turned out he had multiple bad coils, however they would only fail in the #8 cylinder where it was hotter being in the back of the engine. For that reason i wasnt 100% positive it still couldnt be a coil so i just bought a new one. I had previously bought a new coil for another cylinder, so that first swap was with that new coil. I didnt buy two for this exact problem if that makes sense.

When i first bought the car back in August, the first thing i did was put new spark plugs in it. Then later when i started having this problem and the first coil swap didnt fix it i just bought a new spark plug seeing how they are reletivly inexpensive.

The fuel injector was changed for a lean code on Bank 1 soon after i bought the car. I tried pretty much everything else first before i found a bad injector using a stethescope on cylinder #7. I was 90% positive that the #7 was bad, but just to be sure i swapped all bank 1 injectors to bank 2 and vice versa, where the new one for #7 ended up going to #8.

Swapping injectors around is not an easy task, the entire supercharger needs to be pulled, i did it over the course of three days, then spent another 3 weeks chacing vacuum leaks, which i have smoked the engine and there arent any leaks. If i got to that point i will order a new one and just replace it. Its not worth my time swapping them to have to pull it all apart again.

I did mention that I ran BG44k through the car twice, however the first time was with the bad injector, so the #8 cylinder injector has only seen one run of the 44K

 

Did you check fuel trims via OBD? It's normally the only way to be sure there is not even a tiny air leak.

Check at idle, then rev to about 2500 and see what they settle at.

 

 

Hopefully those images arent too big, i uploaded them on my phone.

The first one is at idle and the second picture is at 2500 rpm.

Top are both short term and both bottom are long term. Left hand side Bank 1, and both right hand side bank 2.

Ive tried to learn, but im not quite sure how to interpret them.

 

Can't tell what they are! No key/legends...

Please just put numbers (and what they are).

 

At idle
Bank1 short 0.00
Bank1 long 3.91
Bank2 short 0.78
Bank2 long 6.25

At 2500rpm
Bank1 short 7.13
Bank1 long -0.78
Bank2 short 5.47
Bank2 long 1.56

 

They drop but not from initial big values so you may well have a tiny air leak.

 

While monitoring the fuel trims get a can of carb cleaner and start spraying any suspect connections.

I have a 2005 STR and can guarantee the P/B vacuum line is leaking or soon will be.
Do you know where that is?

When you pulled the super charger did you replace the cooling hose underneath it? That is another for sure repair that needs to be done.
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Not sure what P/B Stands for?

After all the problems I had, I purchased a smoke machine, and it seemed to work quite well. I havent used recently, but the last time I checked I got rid of all the leaks.

I know I should have, but I didnt replace the cooling hose, I should of done more research before I pulled it and had everything ready, but I didnt.

The only place I can think of, if its effecting only that cylinder, would be at the gasket between the heads and charge cooler, but Ill get some carb cleaner and check it out.

I went through two big cans of it before just buying the smoke machine.

 

Sorry. P/B = Power Brake

Take a look at this thread.
https://www.jaguarforums.com/forum/s...-p0174-149418/

It does sound different from yours with your added details but it will show you the problem vacuum connection.

Please keep posting back so we can get it fixed!

Did you use a new gasket? We have had numerous repeat failures when the gaskets are reused.
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Yes, as a matter of fact, that piece did break on removal, and I did have to fix it

After Install of the SC, I had leaks at the EGR Valve (gasket), power brake vaccum line, and the MAP sensor (broke on removal). Literally it felt like I would fix one leak, and then that would reveal another.

Unfortunately again, I really wish i did more research before I pull the SC, but I didn't change the gaskets. They looked to be in decent shape, and in fact didn't even more from the the heads with the charge cooler removed. Its something I really wish I did now, but thats the joy of hindsight

I am not off work till monday. So ill do some more investigating then, including both looking for leaks and doing a compression test.

 

Had a few hours today to work on the car.

Did compressions on all of bank 2, and thankfully they were all good, all of them were between 135 and 140psi.

I also broke out the smoke machine again to check for leaks. Again did not find anything, not even the smallest of leaks. As well as the smoke machine I went through an entire bottle of carb cleaner while monitoring Fuel Trims, and I couldn't find anything.

After doing compressions I swapped the coils again, and the problem still stayed with cylinder 8.

I was worried maybe I had a head gasket leak, from what I read they are quite uncommon but I have found a few on here that have had problems with less miles than mine. I bought the car from a rather shady small time dealer, and I know he replaced the radiator right before I bought it from him. Did the engine excessively over heat before I bought it? I don't know. But I have had a small coolant leak since I pulled the SC, probably from the galley hose under the SC! Its never over heated since Ive had it but I will get a low coolant light every 6 weeks or so, and then it takes maybe 1/4-1/3 a bottle of coolant. But I could see drops under the car after shut down. Anyway I changed the oil today too, the old oil looked fine, and compressions were good, So Id imagine I could rule that out.

I am going to run another bottle of 44K through it, and see what happens.

If that doesn't fix it, I think Im just going to bite the bullet and bring it into Jag just for a diagnostic test, I really don't know where to go from here. ECU?

 

That's the last suspect.

 

Update

Got some good news today.

I pulled apart the motor again Monday, my plan was to send out all my injectors to a local injector cleaning place, and to replace all the gaskets. While I have the engine apart, I have replaced the coolant hose under the supercharger, the DCCV, and the valve cover gaskets.

I got a call from the injector service place today, and he confirmed that the #8 injector was bad electrically. So I just ordered a replacement, and I am having it sent to him so he can flow match it with the other 7.

I am just happy to have pinpointed the problem. Hopefully I will have everything back together next week.