Hi guys I have a 2006 Hummer H3 adventure package I just purchased for 7,900 with 167,000 miles. I noticed the check engine light comes on(p301) randomly and typically happens at idle. The code is p301(cylinder 1 misfire) I replaced the spark plug(oem) and tried a new coil pack and another from the next cylinder and still comes on. What is weird is I can sometimes drive 100-200 miles with no issues even at idle and then magically the lovely cel comes back on..There are times where the light will come off on it's own other times I reset it with a obd scanner. My question is should I be concerned? Next question is if I do nothing and continue driving it as is will I have anything to worry about other than a check engine light? Additionally I tried calling gm about if the head is the original and they weren't able to give me any information. I tried looking for a stamped number on the head but couldn't read the one under the air intake tube(seems to be dot etched) is there another location for head serial number? Thanks!

 

Welcome,
Long before I'd suspect the head, I would be certain I replaced all the coils.
Have you cleaned your MAF, Throttle Body and checked / replaced your air filter?
Also check the cam actuator to see if there are any screens missing...

I see so many post jump to the conclusion its got to be the head.... Sometimes it really is just that simple, others it is a sticking fuel injector..

 

I did clean the maf,and throttle body along with trying coil packs. Also tried a over the counter fuel injector cleaners. Air filter is new. How do I check cam actuator?

 

Ok so just took off the camshaft actuator and inspected it and all screens are in place.

 

Did you remove TB from vehicle for total cleaning?
Did you replace all injectors, spark plugs, COP? With new OEM? Or better quality?
Not vato zone or eBay.....

Are certain the MAF is functioning? You may consider a new ACDelco or equivalent.
I'd stay away from cheap aftermarket....
Also, try using techron. It works!

After all of this if you still trough a code I would then use a scan guage to run down any erratic signals coming from your vehicle. A tool that is indispensable.
It is quite possible to have a crank or cam sensor that has been replaced with a low grade Chinese made part that could be causing an erratic or errant signal.

 

The cam actuator is located at the front left upper bout of the engine. It has one bolt holding it and costs about $60 for an ACDelco part.

 

Video is not mine but a Google search found it in 30 seconds. Lol!

 

Is your 06 even in the Vin# range for that problem?

The S/Ns affected is any 2006 H3 lower than 287591 .... the first one started with 100,001, your truck build date will be Nov. 06 or earlier. Not all have the problem, but some could. The head issue affected not only the I5, 4s and 6s were subject to the same issues.

Do some searching, there is things that can be done to correct your issue, one of them was posted by Hummerz a ways back.

 

Yup my vin does fall into the range..