Posting for a friend 04 6.0

[drakon543]

so a friend of mine has an 04 2500 with the 6.0. its actually a pickup but im assuming the 6.0 is pretty much the same for the pickups and suvs. multiple cylinder missfires only above 2k rpms. most of the missifires are showing on cylinder 1 and 6 i think he said 5 and 8 are also popping up alot. other cylinder missifires too but mainly those cylinders. its only above 2000 rpms and comes with cel flash and pending codes and will immediately go away if he lets off the throttle. it only has missfire codes and runs well outside of that. he has done a tune up swapped the coils swapped injectors and done the intake gasket with no effect. a garage suggested he might have an issue with the afm system/cam or valve springs or something. hes just looking for some other opinions before he pulls the engine apart for diagnosis.

 

[Dantheman1540]

Does it bog down and not let him get over 2k rpm? Sounds like possibly a fuel pump.

 

[OR VietVet]

He said the misfires happen above 2000 rpm, only. IMO, it does sound like a problem with the afm system. The pending codes should still be able to be found and listed here .

 

[Dantheman1540]

Forgive me if I'm wrong but I thought AFM started in 2007

 

[afpj]

Cats?

 

[OR VietVet]

Forgive me if I'm wrong but I thought AFM started in 2007

By golly, I believe you are right. Good call. He did say though that the misfire did not happen TILL he reached 2000 rpm. I want to see those codes before I GUESS at anything else.

 

[OR VietVet]

Cats?

In all my years in the business I have seen cats cause a loss of power but have never experienced a misfire caused by them. Not saying they can't but I have never seen or experienced that problem connected to clogged cats. Especially picking on certain cylinders.

 

[OR VietVet]

James, has the owner had done or did any work to the vehicle recently before this problem started to happen?

 

[drakon543]

nope no problems prior to this issue. no real loss of power or bogging down aside from the missfires. the codes that are coming up are just multiple cylinder missfire code nothing else. as far as afm im finding nothing but conflicting information. arguably gm started afm in 04/05 but only introduced it in the v8s in 07. also nothing but conflicting information if the 6.0 ever even came with afm anyway. 6.2 yes but the 6.0 im finding yes and no. i cant really go look at his truck myself or i could get faster information. but yes as long as he keeps the rpms under 2k it runs great. even if he has the truck running and in park if he gives it enough gas to get above 2k soon as it hits that point missfires start getting posted with a multiple cylinder missfire code.

 

[Dantheman1540]

I just diagnosed an H2 hummer with a LQ4 that did the exact same thing. Get a fuel pressure gauage from auto zone for 19.99 and check it at the port on the passenger side fuel rail. So easy a caveman could do it. It will likely show good pressure 50-60psi at idle and as soon as he hits 2k it will drop to near nothing.