so I have been reading a lot about the p0301 cel code on this sight and everyone is saying that it is a head problem due to soft valve seats.
the question I have is this (this is embarrassing) I have owned my 07 h3 since 2010 and I had the infamous shaking at idle and when sitting at a stoplight start about a year after I purchased it. I have not had it fixed to this day (due to finances and job loss)and now that I have moved to ct I need to do emissions testing and I will not pass as the code is a category one code when it comes to emissions.


so the real question I have is that if I have been driving it for a little over 4 years with just the #1 cylinder misfiring why haven't I had any of the other cylinders misfire? or is there something else wrong with it? other than this issue I have the rig is just awesome and will not get rid of it.


please help.

 

This might be one of those "a little bit of knowledge can hurt you" things.

First, you have a 2007, the TSB and recall regarding the head failure was for ONLY 2006 H3/Colorado/Canyons with a serial number lower than lower than 287591 which will have the 3.5L L52 Motors built before March 31, 2006.

So...... that ain't you.

A P301 can be for a lot of things, you could clear the code today and it might not return for months or ever, go get your test then.

You are more likely to have a bad coil on plug pack for cylinder #1, or a dirty connector where the coil connects to the wire harness, or a intermittent short or frayed wire in the harness to the coil pack, or even just a plain old bad plug in that cylinder. You might just have water that got on top of the head and got the #1 coil pack wet. Easy stuff, no need to make a paranoid jump to assume catastrophic problem.

Remove the intake and inspect the coil pack, the connector to the harness, and wiring to it. If it looks OK, you can swap coil pack #1 with Coil pack #2 (or any other cylinder) and see if the misfire follows the #1 coil pack (if you move it to say #3, and there is still a misfire, and it throws a P0303 code, then the coil pack needs to be replaced.

While you have the intake off, clean the TB and MAF using only TB and MAF cleaner respectively. See this: https://www.hummerforums.com/forum/h...what-do-33916/

All I5s vibrate, inherently unbalanced, just the way they are. If you do not clean the TB about every 30-50K miles, you will get a rough idle and they will vibrate even more.

Last.... continuing to drive a vehicle with a continuing misfire is NOT a good idea, it can do damage to the motor if serious enough.

 

the reason I thought it might be the head was that I saw a thread on this sight that said the problem was for 2006 and only 2007 h3 that were made before feb. of 2007.
I will take your advice and check the items you mentioned. I will post my findings when complete.