Any GM techs? 03 2500hd 6.0L help

pcole0920

Well-Known Member
Joined
Oct 23, 2009
Location
Lexington NC
I've got a 2003 Chevy 2500hd with a 6.0L 87k miles. Truck had sit for 6 plus years in the dry waiting on me to fix it and get it painted. Every time I went to move the truck it ran great with no trouble. Once I got the truck done on the way home it started missing. Code P0300 random cylinder misfire. Onc checked it was cylinder 3 and 4. Ok injections clogged up from old gas. Changed injectior 3 with the injectior from cylinder 1 and injectior 4 with the injectior from cylinder 2. Rechecked and still missing on 3 and 4. Checked the coilpacks and they are good. Checked power to injectiors and they have the proper power. Read that it could need a crank shaft sensor relearn did that with a new sensor and still missing on 3 and 4. Checked MAF and checked everything else I think of. Also truck is very hard to start if been sitting more then a few minutes but will fire right up first thing of the morning also a very bad smell from the exhaust. Only misses at idle also as soon as you get above idle it clears up and it shows it on the graph. I'm at a loss on where to go now. Any ideas would be great. Thanks.
 
Spark plug wires. The stock ones suck. Mine sat for a few weeks and started getting a misfire. I did have a bad coil pack, but it completely went away with new wires. Those two coils packs could be bad. Don't use BWD brand replacements. AC Delco is the way to go.

I'd probably give it a good tune up. Plugs, wires, fuel filter, run something through the next tank of gas to help clean it out, and get out and drive the piss out of it! That'll really help it out. Some WOT runs will blow all the crap out of the cats.

If I'm not mistaken, a set of the MSD (or whatever brand you prefer) wires is cheaper than a set of stock replacements from the parts houses. I want to say they wanted 90 for stock ones and I got MSDs for 70.
 
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It's got a new fuel filter, new fuel pump and new AC delco plugs. Changed the plug wires around and also changed the coilpacks around and it's still on cylinder 3 and 4. Compression text shows great between all cylinders. Ran some cam2 through it as well as some seafoam.
 
A very common issue is the coil jumper harness from the main engine harness to the coils. Many of them will have damaged wires and connectors. Might start with a wiggle test on that portion of the wiring!
 
Does it say anything about running lean at all? Possible intake gasket issues, maybe. Definitely check the coil pack harnesses.

When I pulled the heads on mine to replace the lifters, I cranked it without plugging the passenger's side coil harness back in....couldn't figure out why it had misfire codes! The cam sounded better than usual hahaha
 
I noticed you said you checked the coil packs, how did you check them? Swap them with others to see if it follows. If you have a scan tool check your injector signals with live data. Sitting that long could be a bad connection, vacuum leak. Iv run into a simular problem when I was at gm. Turned out to be multiple things. Take your time and go through the processes, try not to rule anything out without knowing 110%.
 
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Nvm tapatalk didn't show all the messages, seen where you changed them around.
 
Yes I've swapped the packs and injectors around. The miss is still hanging out at cylinder 3 and 4. Did find out my hard start and smell maybe coming from a bad fuel pressure regulator. I've got 2 of them so I'll also check that
 
pcole0920 said:
Yes I've swapped the packs and injectors around. The miss is still hanging out at cylinder 3 and 4. Did find out my hard start and smell maybe coming from a bad fuel pressure regulator. I've got 2 of them so I'll also check that
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Typically a fuel pressure regulator will cause a misfire in all cylinders or will cause a rich condition, not a misfire on 2 cylinders. You could easily verify this by unhooking the vacuum line from the fpr and checking for fuel coming out.
 
I didn't think the FPR would cause the misfire but from what I've read is could cause the hard start and the poor smell from exhaust
 
pcole0920 said:
I didn't think the FPR would cause the misfire but from what I've read is could cause the hard start and the poor smell from exhaust
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From my experiences if it's causing a smell from the exhaust, it'll cause abnormal fuel trims. Easy way to tell is checking your fuel pressures against spec.
 
I just pulled the vac line off of the FPR and it's a steady stream of gas come from the vac port on the FPR. I've got 2 other ones on fuel rails so I'll change that and see if their any change
 
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