2004 Chevy Silverado 2500hd 6.0 gas intermittently won't start on first crank, but not consistently. Have replaced the ignition switch, fuel pump, spark plugs, injectors, crank, cam sensor, ignition coils, and etc. Fuel pump is getting the right pressure. Some times it will take a few seconds for it to start once cranked, like it is struggling to get the right mixture of gas to spark the engine, or it has a delay in getting a spark to start the engine, other times it will just fire up without incident. I am merely guessing at this point. This problem has played me for a long time and can't figure it out, nor can 3 other mechanics, or the dealership. It is not throwing any DTC codes either due to it being pre-ignition. Once the truck starts it runs great. Thanks

 

Could it be a failing PCM?

 

What I also noticed by disconnecting the battery for about a hour and reconnecting the truck starts fine for a short period of time, then it starts again with an extended crank issue. I assume the PCM reverts back to the factory settings by doing so. Would that be correct? Thanks

 

Have you attached a fuel injection system pressure gauge to the engine to see if the fuel injection system holds pressure for an extended period of time (like several hours) or if the pressure bleeds off? Losing the fuel pressure could cause the condition you describe.

If you find that the pressure does bleed off over several hours, you might want to add a bottle of Techron Complete Fuel Injection Cleaner to make sure the fuel injectors are clean and able to hold pressure. If an injector is dirty, it might not seal properly and bleed off pressure over a period of time.

Good Luck!

 

I will give that a try! Thank you

 

Well fuel pump holding pressure, and Techron Complete Fuel Injection Cleaner added, no luck. Any other suggestions? Thanks

 

One last thing to add, may be of value or not. Got a message on instrument cluster tighten fuel cap. Replace with new cap, same issue.

 

Performed a smoke test and saw no leaks. This morning, I disconnected the battery for about a hour and re-connected it. This truck started great with no issues. After about 6-7 restarts the problem re-occurred, and the next crank after that it started fine with some struggle. Could this be a compression issue, or if it was a compression issue would it be consistent, or possibly a weak cam or crank sensor not allowing the timing chain to be in the correct position upon startup? I am searching at this point for something that makes sense if that is possible. Many thanks

 

Did you crawl under the truck and looks for smoke leaks along the EVAP tubing and on top of the fuel tank?

 

I only checked the top side. Good catch, I will check the bottom side next to the evap tubing and fuel tank. I was also leaning towards a possible evap leak, potentially. Thanks for the suggestion.