Yukon Denali 6.2L stalling at idle when hot

[jeepermat]

I have a 2008 Yukon Denali with the 6.2 and 150k miles that I am at wits end with.

It started about a year ago while driving in the mountains of CO, trucking along at 70mph I let off the throttle to coast and it died, pulled off the side of the road and tried a few times to restart, after 10 minutes it finally started. Ran fine and never did it again until this year.

This summer its been nothing but problematic, any time you drive it in traffic when hot it tries to die when coming to a stop at idle, you have to pop it into Neutral and keep the engine above 1000rpm, or it will die. Never sets a code when it does this, it will usually restart after sitting for 10-45 minutes. Always runs fine above 1000rpm.

Ive checked fuel pressure when this happens and it was at 55psi, it looks like many others suspect vapor lock with their 6.2's stalling, however I am not convinced that is the case, I can bleed the rail down to 0, and try to restart and it usually wont.

I had HPtuners hooked up to it after it stalled and wouldnt restart, I noticed when I finally got it going the voltage was hovering around 12.9-13.1 volts, I thought the alternator was possibly the culprit so I replaced it and the negative cable. It still stalls at idle though, and now Ive noticed when it does it the voltage is still hovering around 13V which seems low even at higher RPM's.

Im very suspect that the voltage has something to do with this, however Im not sure whats going on there, the alternator is new and Ive gone through every ground I can find.

 

So far Ive replaced the following

-Throttle Body

-Fuel Pump

-Alternator and battery ground

 

Looking for any other suggestions before I burn this thing to the ground

[riverbanks]

Try unplugging non-essential fuses,see if voltage goes up,or disconnect maf,then try restart,they can underreport

[jeepermat]

2 hours ago, riverbanks said:

Try unplugging non-essential fuses,see if voltage goes up,or disconnect maf,then try restart,they can underreport

Forgot to add Ive unplugged the MAF to try and start it in speed density when its acting up, but still no start.

[Joehoff]

I'm having this exact issue in my 2008 2500hd with the 6.0.  Have you gotten any further?  My mechanic is going to change the fuel pump tomorrow... 

Edited August 27, 2020 by Joehoff

[15SilvyHC]

Maybe try a new ignition coil? Heat can cause expansion and if there are any hairline fractures it can cause issues at operating temp. Only to be resolved once it cools down a little bit. Sounds similar to your problem. Might be worth a shot if it isn't too expensive or you know someone you can borrow one from.

[Kenneth Machado]

Sorry to dig up an old thread.  Did you resolve this?l issue   I’m having this same issue in my 07 NNBS.  Replaced fuel pump, fuel pump control module, and crankshaft position sensor. 

[swathdiver]

3 hours ago, Kenneth Machado said:

Sorry to dig up an old thread.  Did you resolve this?l issue   I’m having this same issue in my 07 NNBS.  Replaced fuel pump, fuel pump control module, and crankshaft position sensor. 

https://www.tahoeyukonforum.com/threads/2007-gmc-denali-stalls-after-towing.73312/page-8#post-1520887

 

https://www.tahoeyukonforum.com/threads/2007-yukon-denali-stalling.111715/

 

https://www.tahoeyukonforum.com/threads/2007-yukon-denali-crank-no-start-after-driving.131974/page-5#post-1668322

 

 

[Kenneth Machado]

5 hours ago, swathdiver said:

https://www.tahoeyukonforum.com/threads/2007-gmc-denali-stalls-after-towing.73312/page-8#post-1520887

 

https://www.tahoeyukonforum.com/threads/2007-yukon-denali-stalling.111715/

 

https://www.tahoeyukonforum.com/threads/2007-yukon-denali-crank-no-start-after-driving.131974/page-5#post-1668322

 

 

Thanks for positing that!  My truck is an 07 NNBS with the l76 6.0.  I have a black bear tune with afm disabled.  I am noticing lower oil pressure when idling.  Could that be my issue?

[swathdiver]

2 hours ago, Kenneth Machado said:

Thanks for positing that!  My truck is an 07 NNBS with the l76 6.0.  I have a black bear tune with afm disabled.  I am noticing lower oil pressure when idling.  Could that be my issue?

Not unless the pressure is at zero.  These aluminum engines run at low pressures, mine when hot, with old oil, is in the low 20s at a stop light for example.

[Kenneth Machado]

4 hours ago, swathdiver said:

Not unless the pressure is at zero.  These aluminum engines run at low pressures, mine when hot, with old oil, is in the low 20s at a stop light for example.

Thats good to know.  i`m not sure where to look next, maybe the throttle position sensor?

[swathdiver]

11 hours ago, Kenneth Machado said:

Thats good to know.  i`m not sure where to look next, maybe the throttle position sensor?

 

Well, how low is the oil pressure?  When was the last time you unbolted the throttle body from the intake and cleaned it?

 

Walmart and local auto parts stores have this.

[Kenneth Machado]

I cleaned the throttle body and mass air flow sensor last week.  Oil pressure is ~ 18PSI at idle, as soon as i touch the pedal it jumps up.

[Kenneth Machado]

Any other updates?  just did a crank position sensor.  we will se how it goes.  not sure what the real "solution" is

[Tfidler]

Same problem here 

[Walker1234]

Replace the under hood fuse block. This fixed majority of my electrical issues and solved the stalling problem. 
if your alternator is charging all over the place this fixed mine to where it stays steady at 14v or higher.