multi mis fire problem
 

I have an 05 silverado 2500hd 4wd 6.0 auto. I get a code of a multi misfire in 7+8. What I have done: switched around to other cylinders, wires, plugs, coil packs, and injectors, discounected battery over night. Still showing the same codes. It seeems to level out after 2k rpms. fuel pressure good, no vacume leaks. Been adviced to do a computer upgrade.

Re: multi mis fire problem
 

A computer tune will not fix that. Your getting a PO300? PO307 & PO308 would be specific for cyl. 7 & 8. Do compression test on all cylinders if one is low or no compression, Check for a broken valve spring on that cylinder.

Re: multi mis fire problem
 

did that, compression is good. I only checked 7+8 though. 7+8 are at the bottom (gravity) of the fuel rails. could there just be **** in them. I did get a little difference for a little while after I put a new injector in +8. I have been using cleaner every fill up. no progress.

Re: multi mis fire problem
 

How many miles? Can you actually feel/hear the misfires or does it run fine? I had very similar symptoms on my '01 5.3 with cyl 1 & 3 and it was a clogged catalytic converter, but my misfires were audible.

Re: multi mis fire problem
 

197,000 (alot) yes, i can feel it at idle. smooths out after 2k rpm. converter replaced about 40k ago

Re: multi mis fire problem
 

problem is getting worse. I was told to take the fuel rails off and give them a good cleaning. do you guys concur

Re: multi mis fire problem
 

I would check for a vacuum leak at the intake gaskets. They usually show up on the end two cyllinders first.