I just got my motor back together and was checking a few things out, decided to pull the plugs and this is what I found:







I have never seen anything like this before. As you can tell it is a DRASTIC difference. Please pay attention to #7 plug as it is soot black.

What could be causing this? The motor (and plugs) only have about 40 miles on them including some WOT pulls.

DETAILS ON MY SETUP:

-heads/cam LT1
-has the LS1 pcm conversion 24x system
-has NGK TR-6 plugs
-has 42lb. green top injectors
-tuned in speed density by Dr. Phil INTIMID8

 

Is it misfiring? Do a compression test.

 

No it is not. Car runs awesome and has great power

 

I wonder how balanced the AFR is between cylinders. Maybe some injectors are dirty.

 

Check the vacuum compensation line for the fuel pressure regulator. If the FPR is leaking, it will dump raw fuel into the rear cylinders.

 

The injectors were suppossedly flow-matched. I have the flow sheet and it all looks good.

Thanks for responding

I just talked with my tuner and he said that it is possible that the rear injectors are seeing more fuel pressure causing it to dump more fuel. I still have my stock FPR on my car and it has 60k miles on it. Without a doubt, I am going to change this out to a new one. Is a stocker the best or would it be a wise investment to get an adjustable one?

 

Could this be caused because I dont have a parallel fuel rail setup? I also have the stock intake, and I have heard it can cause a poor distribution. It has been ported by Ai.

I am thinking it has got to be the FPR. The car is running better than it ever has and idles great and never stumbles

 

What year is your car? Is it a 93, which has the rails set up for batch fire?

Doesn't make any sense if you have a 94-97, if you have the stock "series" rail configuration. Pressure is highest at #8, drops in the sequence the injectors come off the rails - 6 - 4 - 2 - 1 - 3- -5 - 7. Pressure will be higher on the passenger side, highest at #8. Pressure will be lower on the driver's side, lowest at #7.

The stock FPR is not a problem, unless its leaking. That's what you need to check.

 

It is a 96 with the stock fuel rails in series. #7 is the richest by far.

I ordered another new stock FPR and a set of plugs. My tuner also sent me another tune file to try and I will be taking it back to him so he can check things over and do a retune if necessary. It is is HPT Beta, so I need to wait til their support gives me that version so I can upload his new tune.

Do you think this could be tuning related?

 

Did you take the time to check the vacuum compensation line, or do you not feel that is a possible cause?

 

I took that off and it had a SLIGHT smell of fuel ( could have just been the garage from the car being in there all the time and running and just eh exhaust smell too) and it was dry as a bone. No fuel dripping or residue

EDIT: the email my tuner just sent me said to not mess with the FPR just yet and to upload his tune first.