Hi All,

My 2000 XK8 has been sitting for the better part of 3 years. Since I purchased it last November, I have replaced All ignition coils, spark plugs (gapped at .042), and fuel injectors. I replaced both valve cover gaskets and all o-rings. I did a deep top end fuel cleaning including throttle body. New air filter, MAF sensor looks clean. I continue to get P1316 Misfire rate exceeds emissions and P0171 System too lean Bank 1. Today I was getting Misfire Cylinder 2 and 6 at the same time. I would erase codes, and they would come back. I don't notice any vacuum leaks.
My Autel MaxiAP200 is cheap for a reason. It doesn't give me much Live Data. Only Throttle Body Position. I'm not sure where to look next. Front O2 sensors? Wiring harness looks good.
Any help is welcomed and appreciated.

 

That is strange. If you have missfire you would not run lean.
Turn out the spark plug and look if they look "look lean".
I read somewhere that some XK 4.0´s had problems with some ECU failure.

There is a sensor on your engine which detects the missfire (knock sensor) in comparision to the firing order. for my understanding the O2-Sensor does not work "together" with the knock sensor in the first order. That sounds for me more like a ECU problem.

 

I can believe that. I metered out the harness. It seems fine.

 

This may be a complete stab in the dark, but I had a similar problem many many years ago after renewing all the ignition components on an old car. After much frustration and hair pulling, I decided to return the system back to the original components and discovered that the new spark plugs were the cause of all my problems. It may have been only one faulty one but it caused the misfiring issue.

You mentioned that all spark plugs were checked for correct gapping. Did you find it necessary to regap? Many people with more knowledge than me are adamant that modern plugs should never be regapped if they are off, but returned for a new plug. Apparently if the coating on the electrode becomes damaged, it can misfire.

As I say, just a stab in the dark. Good luck with your search.

 

Thank you!

 

You need a diagnostic tool that can measure fuel trims. Do a search on the forum and you will find several inexpensive tools that do real time data. It is very likely an air leak. Have you checked the accordion folds of the intake tube?

 

^^ Yep, check that accordion section for splits and cracks, especially on its underside....

 

did you check with brake cleaner or obly visual for air leaks?

 

Thanks to ALL responders! Bingo! The accordion Tube looked like it was chewed in 3 sections. I patched with an epoxy, but I'm still getting P1316 (Misfire rate exceeds emissions), and P0171 (Too Lean Bank 1). I'm also getting sporadic Cylinder 2 and 6 misfires at the same time. I'm leaning towards another ECM. I checked with carb cleaner to no avail.

 

I would continue the air leak checking since the car is still reporting that as a possible cause before suspecting the ECM. There's quite a few seals that air can sneak past...
Even my cheep n' cheezy bluetooth ELM327 + Torque app will report fuel trims.

Run a compression test to eliminate low compression as a cause for the misfires.

 

Thank you!

 

Patch needs to be 100% air tight.

Suspect ECM the very last item. They are very robust.

 

Roger that! I think I still have a leak somewhere, but I cant seem to find it yet! If it is on Bank 1 Should I concentrate on the Passenger side?

 

Don't just guess and throw parts at it. Smoke test it and be sure the first time.

 

I need to find someone to do it. I don't have a smoke machine.

 

You can build one, look on utube or buy an inexpensive one on ebay.