2007 GMC Denali stalls after towing

[Cincikid]

" 2008, when I tow I constantly watch my torque app which has oil pressure and temperature. When cruising, pressure stays around 38 to 40 PSI, when idling it stays anywhere between 15 to 20. Oil temperature was running usually between 230 to 240."

15-20 psi hot idle is too low, this makes it highly likely that your problem is caused by the typical VVT/ low hot oil pressure problem. You can read the cause and solution details earlier in this thread: https://www.tahoeyukonforum.com/thr...stalls-after-towing.73312/page-7#post-1519861

Have you solved the issue by switching to a thinner oil?

 

[HD_LS]

Have you solved the issue by switching to a thinner oil?

You need a thicker oil. The hot oil pressure will be determined by the second number in the viscosity rating (the "50" in 5W-50, 10W-50, 20W-50) Choose one of those grades of oil. That will give you a good bit more hot oil pressure than running 5W-30 or 10W-30.

 

[DavesTractor]

You need a thicker oil. The hot oil pressure will be determined by the second number in the viscosity rating (the "50" in 5W-50, 10W-50, 20W-50) Choose one of those grades of oil. That will give you a good bit more hot oil pressure than running 5W-30 or 10W-30.

I agree. I just joined to share our experience in order to help others. My son has a 2008 Yukon Denali with the 6.2 at 180k miles. On long trips, he would sometimes get a stall when coming off the freeway. It would take 20-45 minutes before it would restart. Then it became more frequent, especially in the summer. Fuel pressure was always good. After checking cam and crank sensors and actually replacing them just in case, we still had the problem. When it would stall, we had proper fuel pressure as observed by a gauge, we had spark, and obviously, we had compression. That left timing as the only possible problem. We then monitored cam timing when it died and it was about 50 degrees off where it should be at an idle. 07 and 08s have up to 62* in cam timing. It was enough out of time that even a spritz of starting fluid into the throttle body would do nothing....and we had spark. As HD_LS has said more than once, this is a timing issue for many folks with good fuel pressure. Why? Low oil pressure. Long runs or pulling a trailer or running hard up hills will heat the engine oil more than normal. That thins it down. We were at 11psi hot oil. We changed to 10-40 and put in a bottle of Lucas and we now have not been able to observe anything under 22psi at hot idle. Cam phaser now works as it should, no more stall, etc.

We can then discuss why the low oil pressure and so forth. Briefly, the oil pickup tube o-ring is easy to check. It gets complicated from there, and a shop will often want to replace the engine. But depending on the situation, you might be able to change the oil and add Lucas and get quite a few more miles out of the engine. It's a bit of a bandaid, but it works. There is likely a little more clearance in the cam bearings, the oil pump, or the rods and mains than when new. A little thicker oil fills that gap and restores oil pressure, and will probably prolong the life of the engine.

I do not want to say that all the "hot stall with a hard restart issues" are oil pressure and cam phaser related. You still need to check codes, check fuel pressure, etc. But for sure put this in your bag of tricks as you diagnose.

 

[JEFFC]

Agree with all of what D said above. My problem was the vapor lock issue and wanted to point out that fuel pressure was normal during the no start condition. Don't assume it's not vapor lock just because fuel pressure is normal. Bleed fuel from rail with several key cycles and if it fires up, you found your problem.

 

[oldtimer]

I tried thicker oil (15W-50 M1).
Increased hot oil pressure from 16ish to 25ish PSI.
Thought that would fix problem, just like after insulating fuel rails, and replacing crank & cam sensors, and replacing fuel pump.
NOPE.
Long pull up Kingsbury grade,
air temp 77*,
tranny temp 217*,
coolant temp 259*,
oil temp 282*
oil pressure 40 psi.
Took foot of gas pedal, engine died.

Left key in on position, hooked up Tech2, no codes set.

Sat for 45 minutes while things cooled off,
tranny 187*,
coolant 198*,
oil 216*,
Restarted and ran like never any problem.

Ordered a Lithium jump start battery to power Tech2, so I can record Cam Retard angles when cranking engine.
Next step may be to replace oil pump (& O-ring), camshaft, and all VVT hardware . . . or maybe a 6.2L crate engine with warranty.

 

[JEFFC]

Oldtimer, have you tried bleeding fuel off from the fuel rail while the no start problem exist? Did you also wrap the fuel line running to the fuel rail and over the top of trans?

 

[DavesTractor]

Jeffc, thanks for that response. Good to know that fuel rail pressure does not in any way rule out vapor issues. We bleed fuel several times and always had pure fuel, no air. What got us going on the fix for our problem was the fact that we had spark and fuel and it cranked but would not start. That pointed to timing. I've read of several cases that were for sure vapor lock, so that can absolutely be the issue. Therein lies the problem, there are several things that can cause very similar symptoms. Having a method to diagnose them in an orderly fashion would be nice. We kind of poked around until we found the timing issue.

Oldtimer, good idea to record cam timing to see where it is at when it stalls.

 

[Fless]

I tried thicker oil (15W-50 M1).
Increased hot oil pressure from 16ish to 25ish PSI.
Thought that would fix problem, just like after insulating fuel rails, and replacing crank & cam sensors, and replacing fuel pump.
NOPE.
Long pull up Kingsbury grade,
air temp 77*,
tranny temp 217*,
coolant temp 259*,
oil temp 282*
oil pressure 40 psi.
Took foot of gas pedal, engine died.

Left key in on position, hooked up Tech2, no codes set.

Sat for 45 minutes while things cooled off,
tranny 187*,
coolant 198*,
oil 216*,
Restarted and ran like never any problem.

Ordered a Lithium jump start battery to power Tech2, so I can record Cam Retard angles when cranking engine.
Next step may be to replace oil pump (& O-ring), camshaft, and all VVT hardware . . . or maybe a 6.2L crate engine with warranty.

Not sure it's germane to the current issue, but that coolant temp seems awful high.

 

[oldtimer]

Oldtimer, have you tried bleeding fuel off from the fuel rail while the no start problem exist? Did you also wrap the fuel line running to the fuel rail and over the top of trans?

Jeffc,
Yes & No.
When it died in Beaver Utah I vented the Schrader valve on insulated fuel rail, it sprayed liquid gas every where, so no vapor lock. Therefore I did not try to insulate fuel lines behind engine and transmission.
Also, since it died in front of Napa store, I tried ether into intake with no start. Since I had ether and time to wait, I sprayed ether on ECU and other sensors to see if chilling them would allow restart. That's when I bit the bullett, and had dealer install new fuel pump. Old pump was borderline bad, but still had hot stall issue.

Not sure it's germane to the current issue, but that coolant temp seems awful high.

Fless,
I thought it might be high, but dash gauge never shows much above 240ish, has redline at 260, and cooling system has never expressed any coolant.
259* is what OBDwiz displays on laptop computer, along with above oil and tranny temps.
I am more concerned with 282* for oil temp, but that may not be excessive.

Would appreciate comments on oil temp, and I may add an oil cooler.

 

[avalonandl]

Add oil cooler is my suggestion