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2012 Yukon XL Denali 172000 miles 6.2L. Owned for 10yrs and no problems until early last year

testdepth

By testdepth
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testdepth New Member

testdepth

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Posted

For the first 9yrs no issues and now this.  I have had this random problem for a year now. It will run fine for several weeks. No engine problems for 100's of miles and then today: Truck is cold when this happens (not yet at normal operating temp of 210F). No noises, no codes or check engine light. Drive down the street 2 miles and from a stop sign turn left and start to accelerate when the truck starts surging, RPMs jumping and acting like it will die. Sometimes it dies and sometimes it doesn't. Once the engine is warmed up it does not do this. Always happens before engine is at normal temp and less than 45mph.  Sometimes I get in like yesterday and it sat all night and drives just fine no problem. Very random problem and the majority of the time the truck starts and drives just fine. Over the last year I have installed:

New OEM fuel pump and sensor

New throttle body

New MAF sensor

New crank sensor

New fuel injection sensor

New coil packs and plugs

New EVAP purge solenoid

New coolant temp sensor

New OEM negative battery cable set

 

I have tested the fuel pump pressure with gauges and pressures are normal at idle and while driving

I have been told this maybe a ground problem but I cannot find a diagram to show me where all the grounds are for this truck.

I have a TOPDON bidirectional scanner.

I'm at my end and ready to plant tannerite in this thing!

 

Any help please?

 

 

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

This to me is screaming of an intake manifold gasket leak. Those can seal up tight when warm. You're feeling a lean misfire when cold, is what I'm guessing.

 

Good way to test is with a bottle of water with a hole poked in the cap. On a cold engine, squirt the water along the intake manifold mating surfaces at the cylinder heads. If it's bad enough you'll actually hear the water getting sucked in, and the tailpipe steam will get extra thick.

 

Any change in the way the engine runs after squirting water along that junction is an indication of a leak.

 

Since the engine is cold, the fueling isn't relying on many (or any) sensors for inputs - that's why you're not getting a flashing check engine light.

 

9 years with no trouble - that's a KEEPER! 

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