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Jeffrey majeske
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Jeffrey majeske New Member

Jeffrey majeske

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Posted

Thank you for stopping to read my post and potentially add vital information, I am so grateful for any information I can get on the matter. 

 

So I own an 2008 GMC Sierra 1500 2 wheel drive. Issues started mid way through 2020. I was driving home one night and I started to feel the truck misfire. Shortly after that, the check engine light started flashing confirming what I was feeling. I got home pulled the codes and had a P307 code. Misfire in the 7th cylinder. At this point I started with the basics. I switched coil packs to see if the problem followed the pack but it did not. I then replaced the injector with a brand new ACDelco injector. No change. So then I replaced all of the spark plugs/wires, no change. At this point I decided to take the truck to the local GM dealer to have them look at it. They had the truck about a week and told me they did all the same things I did and that and concluded that they believe the heads needed to be machined. They told me that they believe cylinder 7 valve might not be seated properly and that I should do a valve job. They said they could replace the motor for 7K or I could take it and have the heads machined because they couldn't do it there. Heres where things get interesting. When I went to pick the truck up it ran worse than when I brought it in, I couldn't even cross the street without the truck stalling. I had it towed back to my house and went to work myself. After a little research I found that a faulty MAP sensor could cause the issues I now seem to be having so I changed the MAP and MAS sensors with a new ones and it immediately helped with how the truck ran. It started running much better but I was stilling having a misfire issue. I then removed the heads and took them to a machine shop where I was informed that there was not enough material to have them machined. The truck has 100K miles but the shop said they looked like they had 200-300K on the heads. At this point I needed to buy new heads. Heads were around $1600 so I decided to get a remand motor for $3200 from rock auto which came with new heads. I replaced the old motor with the rebuilt, new water pump, harmonic balancer, all new injectors, plugs and wires. after I got everything buttoned up and fired her up I had THE SAME ISSUE. P300 (random misfire) at first but then it went back to P307 (7th cylinder misfire). So at this point I replaced both Knock sensors. I also have a Diablo computer that can show 7th cylinder misfire counter and it continues to count misfires every time I run the truck. So your all caught up. I have a new, remand motor, new knock sensors, new harmonic balancer, new plugs, wires, injectors, MAP sensor, MAF sensor and I am still having a 7th cylinder misfire which also disables stabilatrack. I would LOVE and insight I might be over looking or suggestions of things I can try next. Im thinking crankshaft sensor or PCM (Computer) next. HAS anyone reading this ever had a problem like mine? and Info? PLEASE I NEED YOU and YOUR KNOWLEDGE 

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