2003 D2 with 103k miles. My dad was tasked with replacing the HG on my sisters D2. It was obvious it was losing water and throwing misfire codes and o2 sensor codes and running really rough so we figured it was time to do a HG job. Note, I do realize the HG job will not fix 02 codes. Replaced old parts with ngk plugs, 8mm wires, heads planed and valve job. My dad put it all back together and it started up and runs smooth until... It started throwing a misfire in the 2,5,8 cylinders. He made sure all the connections were good on the plugs a even swapped out the coils with some spares and started it back up. It seems to be running smooth but it is now throwing misfires in the 5,6,7 cylinders. He pulled the plugs and the 5,6 cylinders were black already where the rest were fine. What could be causing these plugs to be black already? I would imagine it is fuel related but not sure where to start. Do you think the 02 sensors are causing the misfires because it doesn't seem to be the same cylinders all the time. Any suggestions on where to start in curing the misfires?

 

I would clean your MAF first and see if that helps any. It cheap and easy. Make sure you clean the MAF when it is completely cold (like after sitting over night) and only use a MAF specific cleaner.

Are you still getting O2 codes? To answer your question, Yes, O2 sensor could cause your misfire. I would at least replace the 2 front o2 sensors if you have never done so.

 

Thanks got the reply, I have always thought the MAF sensor malfunction has its own code. I am replacing the O2 sensors currently but wanted to hear any ideas before I drop $400ish into four new sensors. I will let you know of they solve my problems.

 

Jared, the first sentence was to say: thanks for the reply. The other is a bit rude. I do not want to sound unappreciative, any advise is helpful.