Hey all, so over the last six months or so I periodically get a P0300 random cylinder misfire code. I have a 2008 base, and from what I've read this could be anything from heads to coils to plugs. From my research it seems like 2006 models had the problems with the heads but I couldn't find anything for 2008s with that. I inspected my coil packs and plugs last night with no findings, and the plugs are new about 20k miles ago with OEM. I only get the code when I am idling in colder weather and after a day or two it goes away. I did replace the VVT position sensor which seemed to help with overall performance. Any ideas before I start guessing and replacing coils?
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P0300 code 2008 3.7
- Thread starter odwah
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K0PIR
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We're the plugs gapped right?
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Head issues can happen on any year, but hopefully it's not that and many more likely issues ahead of that. Not sure it would be a coil issue as often you'd get a specific error, i.e. p0301 pointing to cylinder #1, etc.
Double checking the plugs is a good idea. Cleaning the MAF sensor would be good, as well as the throttle body. P0300 is just a general misfire and many things could contribute. Since you indicated it happens on cold mornings, it could be temperature related meaning some component is not functioning as well when cold but works better when it warms up.
Are your engine temps correct - the thermostat is about 50% once the engine is warm? Not sure it would tie in, but who knows if an open thermostat could lead to other issues.
Double checking the plugs is a good idea. Cleaning the MAF sensor would be good, as well as the throttle body. P0300 is just a general misfire and many things could contribute. Since you indicated it happens on cold mornings, it could be temperature related meaning some component is not functioning as well when cold but works better when it warms up.
Are your engine temps correct - the thermostat is about 50% once the engine is warm? Not sure it would tie in, but who knows if an open thermostat could lead to other issues.
I could definitely recheck the plug gaps. I cleaned the MAF and that seemed to just generally make things run smoother. I did a throttle body cleaning about 25k miles ago, I supposed I could go in and do that again. Running temp is usually right under half. I've read that a bad belt tensioner could cause this since it wouldn't be adjusting correctly during idle, not sure how I would check that though. I'll take a look at the plugs tomorrow and get back with you guys. Thanks!
Happy Hummer
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Definitely could be idle pulley.
I'd get pre tensioner & idle pulley and replace them as they are relatively cheap-ish...
I'd also replace spark plugs again and all my coils. Having back ups for some rainy day is always good.
I'd also clean the maf & tb again.
Gf's 06 H3 has had a bunch of these issues and short of tearing everything out or paying dealership prices this was the easiest solution. Bolts on intake tight?
I'd get pre tensioner & idle pulley and replace them as they are relatively cheap-ish...
I'd also replace spark plugs again and all my coils. Having back ups for some rainy day is always good.
I'd also clean the maf & tb again.
Gf's 06 H3 has had a bunch of these issues and short of tearing everything out or paying dealership prices this was the easiest solution. Bolts on intake tight?
CaddyStrophic
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When I had these issues, it was the coil packs.
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