Random misfire/oil on spark plug, codes P0301 and P0300

RICKYSH11

MEMBER
2005 CHEVROLET TRAILBLAZER
4.2L
6 CYL
4WD
AUTOMATIC
210,000 MILES

I started getting some really bad misfiring on the way to work one morning. I used my code reader and picked up a P0301 and then P0300. So I went and got a spark plug to change the one on cylinder one. After doing so the engine still ran rough. I decided to change all of them and coming onto the third cylinder I found oil in the well. The plug was fairly saturated with oil. This was the only one like it. After reading about possible causes, it seems that I will have to remove the valve cover to replace a gasket for the spark plugs. Is there any information as to what exactly would need to be done? I usually do most of the work on my vehicles but do not really know the starting point for this job.

5 Replies

KEN L

MASTER CERTIFIED MECHANIC
47,452 POSTS

Hello,

It sounds like the valve cover gasket is causing the problem. Here is a guide to show you what you are in for when doing the job and diagrams with instruction below on how it is done on your car:

https://www.2carpros.com/articles/replace-valve-cover-gasket

After you are done I would check the MAP sensor which can be off a little causing a random misfire code.

Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.

Cheers, Ken

Images (Click to make bigger)

SPONSORED LINKS

Was this

answer

helpful?

Yes

No

Monday, June 11th, 2018 AT 11:50 AM

RICKYSH11

MEMBER
74 POSTS

Thanks, that was very helpful. I finally finished the job of replacing the gasket and I changed all the plugs as well. After doing so I started it up and still had some really rough idling along. I have not checked the MAP yet but will do so next. I did notice however the battery may be in need of replacing it is a few years old and is not the best quality and the alternator may need replacing as well it is original to the vehicle, I am sure if that would contribute to the issue or not.

Was this

answer

helpful?

Yes

No

Thursday, June 14th, 2018 AT 9:26 PM

KEN L

MASTER CERTIFIED MECHANIC
47,452 POSTS

Oh yes, the battery and alternator must be in good condition because the ignition system depends on a clean (no turbulence) voltage supply. I would replace them and clean the battery cables. Make sure you use OEM spark plugs and coils also can you run the codes again?

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

and

https://www.2carpros.com/articles/everything-goes-dead-when-engine-is-cranked

Please run down this guide and report back.

Cheers, Ken

Was this

answer

helpful?

Yes

No

Friday, June 15th, 2018 AT 10:25 AM

RICKYSH11

MEMBER
74 POSTS

Hey thanks again. I ended up finding the issue to be the ignition coil on cylinder one. I checked the battery and the alternator and ran the codes again, both were good. I had gotten a code for P0301 and since I already changed the plug I tried a coil and the misfire is gone and so far it is running normally.

Was this

answer

helpful?

Yes

No

Friday, June 15th, 2018 AT 4:47 PM

KEN L

MASTER CERTIFIED MECHANIC
47,452 POSTS

Nice work. It sounds like a coil issue. Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help.

Cheers, Ken