As I previously mentioned my 07’ Hummer H3 has been having some idle issues. When the rig is cold the idle stutters and stumbles usually turning on the check engine light. This increases as it warms up but then once it gets to full running temperature the problem stops completely and it runs normally.
Looking at forums I was really concerned the problems were due to a bad head. Apparently the 3.7 L engines have real problems with the head. In fact speaking to the previous owner he already had the head replaced once under warranty. But rather than freak out I decided to start simple and go step by step.
I bought a code reader to figure out exactly why the check engine light was on. It said the code was P0305 which was reporting a misfire on cylinder 5. So to begin I decided to pull the spark plug on cylinder 5 and see how it looked. I pulled the ignition coil and got a wrench on the plug but it would not budge. I got a bigger wrench and tried again but no dice, it would not move. I was a little afraid I would break it off and then I’d be hosed.
Instead I thought I’d just switch the ignition coil from number 5 with the one on 4. If the error moved to cylinder 4 then I would know it was the ignition coil causing the problem. But to my surprise after the switch the problem disappeared. No stumbling, no check engine light, nothing but a smooth running engine.
I’m a little baffled by this but I’m not going to complain. As long as it’s happy then I’m happy. I’ll take what I can get.