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Running issue with my 6.0 p300

981 views 1 reply 2 participants last post by  Nored 
#1 ·
Hey,

I've been researching my issues and it seems like I am always linked back here, so I decided to make an account. Going to give a back story if it helps any, and because I like to type. lol.

Last year, I bought a 2001 Chevy 2500HD 4x4 with a 6 inch rough country suspension lift and 36 inch military tires. Has headers, unsure of brand. When I test drove the truck, the check engine light was on, and the truck seemed slow. Being the dummy that I am, I thought it was just slow due to the large tires. Transmission gave out a week after I bought it, and I had it rebuilt. The guy told me the check engine light was on because it needed a tune up, so I told him if he performed the tuneup, I would buy the truck. He called me a week later and said he had performed the tune up, and sure enough, the check engine light was off. On my way home the check engine light came back on, I think all he did was unplug the battery, but I don't know. Also, I found out later that this truck was not treated well at all, so I have no idea what maintenance was done when, truck has 180k miles. IT also burns a quart of oil every 1000 miles.

So... I have that P300 random misfire code, which apparently, can mean just about anything lol! When I had a friend who worked at a dealer, we hooked up the truck to his machine. Rear 2 cylinders had a really bad misfire, and the other cylinders were misfiring occassionly. I pulled the sparkplugs, and they were worn out champions. I replaced with AC Delco. I have also replaced the fuel filter, the PCV valve (Which had ALOT of gunk in it) and checked the spark of the rear 2 cylinders using a spark tester. Spark was fine (Blue/purple). I've tried to run lucas injector cleaner, and seafoam, through 2 different tanks with no success. Right now, at idle, the CEL flashes. IF I floor it, the CEL flashes. IT stumbles really bad at acceleration. The rear 2 cylinders is where my biggest misfire is.

So, before I go on the chase of trying to get the truck running right, I wanted to make this thread to make sure I am on the right track. Right now, at idle, the CEL flashes. IF I floor it, the CEL flashes. IT stumbles really bad at acceleration. The rear 2 cylinders is where my biggest misfire is.

Plan: Test fuel pressure at o'rlys. Clean MAF sensor and throttle body with carb cleaner. Check the intake for leaks with carb cleaner. Check compression. Mail in the rear 2 injectors to an ebay seller who rebuilds them.

If there is something I am missing, or I should approach differently, please let me know.

Thanks!

Devin
 
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#2 ·
So I have been battling the same issue for 2 months. Took it to a shop spent money for them to come up with B1S1 O2 sensor was bad. They replaced it and told me that the plugs needed changed and the alt was bad and most likely the cause of the problem. So I changed the alt and the plugs and within 3 days the problem was back. I have tested and tested and searched the forums and have done everything possible short of taking it back to the shop.
In my search of an issue I noticed my conduit on the harness that leads from the Underhood fuse box down to the frame on the left side was broken in several places so I took it apart and checked all the wires there to make sure were all good. Everything checked out so I replaced the conduit with new and secured it. As I was looking around I noticed that the harness that came off the PCM up to the underhood fuse box was touching the battery tray. when I pulled it off one of the wires was rubbed through and had been shorting out on my battery tray. I repaired the wire and added extra protection to the harness and that seems to have solved my problem.
Just thought I would share and hopefully help some to find this problem as well. You would never see it if you don't take out the inner fender liner.
 
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