First, let me give a little history on my car: '03 3.0...I had lean codes for both banks earlier in the year. I knew my IMT o rings were leaking, so I went the long route.

While I had the intake off, I decided to go down to the cam covers. Replaced spark plug boss seals, cam cover gaskets, new plugs and coils, and new green upper and lower intake gaskets, imt o rings, TB o ring, cleaned MAF and TB, new brake booster and fitting, all sequence tightened and torqued as per JTIS...

Test drove car, seemed ok, but felt a slight roughness at idle, no codes.
Seemed to get worse as car idled.

Checked long and short fuel trims hot, at idle and at 2500 rpm, looks good.

Took out for a ride another day , got the flashing MIL! light went out, went immediately home, then the MIL stayed on for the above codes.

I swapped a coil for one of my old ones, same engine stumbling. Checked coil plug wire plug,supply voltage good, ground resistance ok.

Any ideas now what it would be? Im not thinking ECM, because I didn't get any trigger codes, which is why I didn't check the other two pins ( 4 pin coils). Hopefully I didn't disturb the wiring harness performing above work.

Also, spark plug well is bone dry, no oil.

Time is short, and its getting chilly here. Any ideas would be greatly appreciated before its off to the local indy shop! Sorry for the long post, I wanted to give all details.

Thanks for any input!

 

Given you seem confident that everything went back together ok particularly the upper/lower gaskets.
Have you checked the fuel regulator pipe at both ends and the elbows for splits?

Did you find much oil in the manifold?

 

Swapped coil and ... did you clear the codes AND later get the same P0303?

 

as Jag V8 is possibly about to suggest you need codes and STFT's.
I dont think you put in the code above?
but it is a 2003 3.0L?

 

No, I swapped coils, new for old ( of which is okay), and I didn't clear codes because there was still a rough idle.

 

I'd have done a clear to see if the code stayed the same.

If it does then maybe wiring etc.

 

Sorry, got ahead of myself writing. The codes are of course P0303, and P1316 ( misfire rate exceeds emissions).

Yes, its a 2003 S Type, 3.0 base model.

I didn't have much oil, if at all in the manifold.

STFT's were fine,

 

What about the #3 fuel injector? I didn't see any mention of that. Other than having to remove the big intake plenum for access, it would be easy to swap the suspect injector with a known good one from the other bank and see if the problem follows.

 

If it's easy. Usually they have sealing O rings that ought to be renewed and I'd hate to introduce a new fault.

We don't see many injector issues, especially with a misfire code, but that doesn't mean this one is necessarily OK!

 

UPDATE: Car is running well again!

Even though I put a new set of plugs in when I did the above work, I figured why not change the new plug again, although I thought it was a long shot, what were the odds of one being bad, new, out of the box?

Well, I swapped my new plug out for an even newer one. I put my new coil on plug back in, cleared my MIL from last time, started the car up, she ran great!

Took it on a 40 mile test ride yesterday, and 35 miles to work this morning, no MIL, runs smooth.

Who would've thought it was a new, bad spark plug. I'm still in disbelief, but whatever works!

 

Great news, thanks for the update. New bad parts can be a troubleshooting nightmare. Rare, but it happens. Glad you got it figured out.