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.

 

[OR VietVet]

I should have asked earlier. How many miles on this engine?

Found this at a Silverado forum.

"I have seen several 6.0 trucks through my shop with higher rpm misses. Most of the time it needed a mass air flow sensor and a crank relearn to fix it. I have seen a few intake manifold gaskets leak too. There is an updated gasket out from GM.

I would start by spraying around the manifold when the engine is stone cold and then when it's hot. If your scanner shows live data, it's better to watch for a change in short term fuel trim while spraying. RPM isn't always a great indicator. If you don't have access to data, disconnect the IAC (if you have a throttle cable truck) prior to spraying

Ohm check the injectors too. Look for all of them to be within a few tenths of an ohm.

A crank relearn will need to be done with a factory capable scan tool"


Plus, like Dan said, no harm in getting a fuel pressure reading when you rev engine above 2000 rpm.

 

[01FormulaTA]

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.

AFM was not in any Gen 3 LS motors. A 2004 2500 will have a Gen 3 LQ4 6.0, no LQ4 ever had AFM. Also, no GM 2500 has ever come with AFM. There are many different variations of the Gen 3/4 6.0, no Gen 3 engine has AFM, however some of the Gen 4 6.0s did have AFM and some did not.

Off the top of my head:

6.0 No AFM:
LQ4, LQ9, LS2, LY6, L96

6.0 w AFM:
L76, LFA, LZ1

As mentioned above sounds like a Vacuum Leak or Fuel Pressure issue

 

[drakon543]

AFM was not in any Gen 3 LS motors. A 2004 2500 will have a Gen 3 LQ4 6.0, no LQ4 ever had AFM. Also, no GM 2500 has ever come with AFM. There are many different variations of the Gen 3/4 6.0, no Gen 3 engine has AFM, however some of the Gen 4 6.0s did have AFM and some did not.

Off the top of my head:

6.0 No AFM:
LQ4, LQ9, LS2, LY6, L96

6.0 w AFM:
L76, LFA, LZ1

As mentioned above sounds like a Vacuum Leak or Fuel Pressure issue

that corresponds with the majority of the information i found. guy is a pretty good mechanic but he is more of an old school muscle car guy. said he did the intake gasket as a vacuum leak was something he had already considered. i tell him to recheck for vacuum leaks and to check his fuel pressure.

 

[drakon543]

as far as the injectors unless a whole bunch of injectors went bad i cant see it being injectors related. he was trying to narrow it down so he swapped injectors from the 2 worse cylinder missfires with the 2 best cylinders. but again he is having missfires across the board its just primarily showing misses on 1 and 6 and 2 others. all cylinders show missfires just 4 cylinders have noticeable more. so something that can effect the whole process seems to me more of a culprit. as stated vacuum leaks fuel pressure. he can do live data but its a more basic advanced scanner definitely not a tech 2 so a crank relearn isn't going to be a diy for him.