help even the dealer is stumped

[riddled]

2012 gmc Sierra 2500 Denali

Codes p0192 p2463 p2459

Recent repairs
Under extended service
Injector in Def system
Def tanks and heaters

These repairs have cleared the codes now

Symptoms
Running rough. Loud knocking at higher rpm. Now it's giving no codes and running even worse.. dealer mechanic says it sounds like like a piston knock. Changed fuel and filter. All oil changes ate up to date. Recently had a low coolant which was low with no leaks and I topped it up. Any insight into this mystery would be great. Before the dealer start ripping motor apart which may or may not be covered under power train

 

[IOWA LLY]

They shouldn't just start "ripping apart the motor".

Make them diagnose it.

Have they performed any diagnostics on the fuel system other then a new filter?

Compression test?

You said it's leaking coolant but no external leaks. Have they pressurized the system and checked for leaks? Perhaps the egr cooler is leaking coolant internally...... Could be heard gaskets but I've never seen them cause a motor to start knocking or run rough.

Personally my bet is on the fuel system. Probably another cp4 pump going bad and sending debris into the injectors.

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[Burn Down]

They shouldn't just start "ripping apart the motor".

Make them diagnose it.

Have they performed any diagnostics on the fuel system other then a new filter?

Compression test?

You said it's leaking coolant but no external leaks. Have they pressurized the system and checked for leaks? Perhaps the egr cooler is leaking coolant internally...... Could be heard gaskets but I've never seen them cause a motor to start knocking or run rough.

Personally my bet is on the fuel system. Probably another cp4 pump going bad and sending debris into the injectors.

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This ^^^^ My guess is fuel system as well.

 

[ALLY Fox]

Dealers don't always have the most experienced & knowledgeable diesel mechanics, but you are probably stuck with them since it's extended warranty work. I would agree with the others, probably fuel system related. I've seen diesels sound like they are knocking themselves apart due to a simple injector harness issue. Don't let them "shotgun" a solution, they've already "fixed" it once.....

 

[NC-smokinlmm]

Have them drop the tank and look for metal shavings in the bottom. Is the cp4 making commanded pressure? To be honest, I'd go find a dealer who has a capable mechanic, not all techs are created equally...

 

[riddled]

Thanks guys I'm headed there in the morning

 

[Gil714]

You need to check the provisions of your extended service contract agreement in terms of getting your repairs authorized by a Certified Mechanic verses a GM dealership. It wouldn't hurt to call the extended service contract company to see, based on your concerns, to see if you can use the service contract elsewhere.

 

[riddled]

Talked to the tech this morning he had already started to see if he can find a problem in the injectors... should know hopefully within the hour

 

[NC-smokinlmm]

Talked to the tech this morning he had already started to see if he can find a problem in the injectors... should know hopefully within the hour

What did he find?

 

[riddled]

Well now with the warmer weather and no issues... it runs fine... they think it may be the pump but all symptoms have stopped for now.. they were talking replacing the while fuel system. But now they are not sure cause it seems to have corrected with no work. Any suggestions would love to hear it.. we did go from -30 to -2

 

[carl.swoyer]

I had the #2 and#7 injectors short out sounded like a hard knocking replaced both and the knock want away

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