2007 Yukon 6.2 stalls/won’t start when hot

[Campie]

Using your scanner what does the MAF read when running in park hot idle?
Not set in stone, but the general rule is. It should be reading about the same as engine displacement. In your case about 6.2g/s
Im guessing if it's under 6g/s you have a vacuum leak that gets worse the more the engine gets heat soaked.
Check the PCV hose connection at the back of the DR side valve cover. The vent hose connection at the front of the RT side valve cover and the seal around the oil fill tube.
Just fixed almost the same problem on a friends Yukon. His would die like yours but start right back up.

Also a low/bad battery will give you all kinds of codes and problems. Once replaced they will still be their till cleared. If they come back, then you might have a problem.

My bad, the MAP was the value I gave before. The MAF reads 9.14 with a calculated air flow of 7.88. That’s hot idle with RPM of 594. EVAP Purge Solenoid 18%. A whole bunch of other readings so if you have questions I can tell you what I see.

We took the camper for a drive Friday and the truck ran great. We drove around, on and off the highway, slowing down, speeding up, all good. Took an exit ramp after a long pull up a hill at 65 on the highway and stopped, waited for it to die but it kept running. Headed up to Michigan this afternoon so this will be the real test! Fingers crossed the battery and cables did to trick!

 

[Campie]

I got a buddy a few shops down that has one of the cop car ones, he was telling me his was doing something like this. turned out to be the tranny. when it was trying to stall he popped it in neutral and it stopped stalling or trying to stall. he bought a new converter, but didn't get around to putting it in.


just something to try.

Interesting! We’ll keep that in mind!

 

[Campie]

That MAF at 5 or a bit higher was after running for about 10 minutes. I’ll get more info when it’s for sure hot.

Sorry, that was the MAP at a little over five, my bad! The MAF is 9.14 at hot idle 594 RPM.

What’s the MAP?

We did the Purge solenoid earlier in the spring but still had the “dying” issue.

You can also wire in some resistors that fool the computer...you can get 5 for $10.
View attachment 464614

Awesome! Thanks so much for this information!

 

[Campie]

@B-train
Have these 2 Technical service bulletins been done?
https://static.nhtsa.gov/odi/tsbs/2012/MC-10138192-9999.pdf
and
https://static.nhtsa.gov/odi/tsbs/2014/MC-10114272-9999.pdf

I will look into both of these Service notes. We are not getting any codes thrown and there is no reduction in power. It’s running great, strong and powerful and then just… nothing.

About the other SN, what I understand is the AFM was not activated yet in this truck. Again, I’ll look into it also.

 

[Campie]

Here's another thought since it happens on decel.

Something I notice when driving and monitoring the Torque Pro app, when decelerating, there's a good bit of Short Term Fuel Trim fluctuation....like 15%.

I wonder of your injector(s) might have a fault and you are getting a very rich mixture on one or more cylinders and the plug(s) are temporarily fouled or wet.

Next time it happens, try a cleared flood mode when starting by holding the gas pedal to the floor while cranking.

Which leads me to ask, how old are your spark plugs, and are they OE AC Delco?

Once a plug is fuel fouled, it won't be right again if left untouched. Maybe they are old and have been fouled before, or the wrong plugs.

So looking at my scanner, I see short term FT Bank, 1 and 2. Both are pretty close to zero most of the time. They both fluctuate similarly, between maybe -3 and + 8.

 

[Campie]

After about 2 1/2 hours on the highway in 90 degree heat we finally got codes! The fuel relay, which we’d planned to replace already but got the wrong part and the crankshaft sensor which I’d also planned to replace but not in a hurry.

At least now we have a plan! Sad that we had to drive all the way back home and get our other Truck but glad that we finally have codes so we can make some progress!

 

[B-train]

After about 2 1/2 hours on the highway in 90 degree heat we finally got codes! The fuel relay, which we’d planned to replace already but got the wrong part and the crankshaft sensor which I’d also planned to replace but not in a hurry.

At least now we have a plan! Sad that we had to drive all the way back home and get our other Truck but glad that we finally have codes so we can make some progress!

Interesting! Good to hear. I also had the crankshaft sensor code, luckily it's an easy fix. The fuel pump relay is one I wouldn't have suspected, but another avenue to check when I get back home.

Keep the updates coming! I'll do the same as time allows.

 

[Campie]

A bit more detail about our drive yesterday: engine radiator temp stayed about normal at about 210 on the dash gauge for the first 2 hours and the tranny temp was around 190. Then the coolant temp crept up a bit to maybe 220 and the tranny went up to 210 or so. About that time we went over a really bumpy curvy ramp and got traction control warning light on and back off about 4 times. All was well for another 1/2 hour til we got off the highway and turned into a parking lot. Then the traction control light and the check engine light both came on. Checked it with the scanner and found the fuel relay code and the crank sensor codes. We tried to find a new relay, but they didn’t have one in stock so we swapped relays with the fog lamps. Then we parked the camper and drove home and got the other truck. The car ran great on the way home and got 17 miles to a gallon on the highway, no problems at all! The coolant temp stayed around 210 but the tranny temp went down to 165. By this time it was around 8 PM but the tranny temp is usually around 160 or 170 except when towing.

Obviously, we will replace that relay and the crank sensor. We will also check with the radiator shop and see if we need to do something to upgrade the radiator. What should the coolant temperature be on average when driving and then when towing? Or should it be the same for both?

Thanks guys!

 

[Fless]

Consider doing a CASE relearn after you change the crank sensor. Doing that might avoid weird P0300 misfire codes and long crank times.

 

[rdezs]

....Fingers crossed the battery and cables did to trick!

That's one of the first things that crossed my mind.... And with today's electronics, it's almost mandatory to start with this to make sure they are getting proper voltage and amperage. Broken and frayed wires inside the cables cause havoc.... Yet on the outside they look just fine. Remember your engine moves left and right slightly on acceleration and deceleration.... I suspect when you decelerate and it moved the engine the other direction, it broke a connection inside one of the cables.

At least now you should be able to attack what's left with some degree of confidence....

 

[B-train]

A bit more detail about our drive yesterday: engine radiator temp stayed about normal at about 210 on the dash gauge for the first 2 hours and the tranny temp was around 190. Then the coolant temp crept up a bit to maybe 220 and the tranny went up to 210 or so. About that time we went over a really bumpy curvy ramp and got traction control warning light on and back off about 4 times. All was well for another 1/2 hour til we got off the highway and turned into a parking lot. Then the traction control light and the check engine light both came on. Checked it with the scanner and found the fuel relay code and the crank sensor codes. We tried to find a new relay, but they didn’t have one in stock so we swapped relays with the fog lamps. Then we parked the camper and drove home and got the other truck. The car ran great on the way home and got 17 miles to a gallon on the highway, no problems at all! The coolant temp stayed around 210 but the tranny temp went down to 165. By this time it was around 8 PM but the tranny temp is usually around 160 or 170 except when towing.

Obviously, we will replace that relay and the crank sensor. We will also check with the radiator shop and see if we need to do something to upgrade the radiator. What should the coolant temperature be on average when driving and then when towing? Or should it be the same for both?

Thanks guys!

Thanks for the update!

Well your story coincides with 2 of 3 failures with mine. 2 were after a sharp turn and/or bump combo after steady driving. I'm still in Puerto Rico and then Jamaica for another week for work, but I plan to work the old girl when I get home and see if I can replicate it and record any data to share. I have extra relays from my generator days, so I'll bring one along.

I'm hoping collective gathering of facts/life experience can help us, and others. It's a weird gremlin for sure.

 

[Campie]

Consider doing a CASE relearn after you change the crank sensor. Doing that might avoid weird P0300 misfire codes and long crank times.

Yes for sure and will try to match the brand used when the cam sensor was replaced.

 

[Campie]

Yes for sure and will try to match the brand used when the cam sensor was replaced.

Thanks for the update!

Well your story coincides with 2 of 3 failures with mine. 2 were after a sharp turn and/or bump combo after steady driving. I'm still in Puerto Rico and then Jamaica for another week for work, but I plan to work the old girl when I get home and see if I can replicate it and record any data to share. I have extra relays from my generator days, so I'll bring one along.

I'm hoping collective gathering of facts/life experience can help us, and others. It's a weird gremlin for sure.

When we went around that bumpy curve at 65 miles an hour, we could feel the camper almost pulling the back end the car around a bit. Kind of like the tail wagging the dog! And decreasing at the same time. Makes sense about the engine moving around at accelerate/decelerate. And there could for sure have been a bit of traction lost from the bumpy road.

Ours runs super strong and stable on its own. The only time we have trouble is really hot, long drives towing our camper.

 

[B-train]

Here's an interesting video for the same type of running condition.

I pulled the purge valve off mine and cycled it with 12v and it works fine. I tried heating it up with a heat gun to simulate a hot engine bay without any definitive failure. But, its not to say that engine vibration with a long heat soak could be the issue. Also the orientation horizontal vs my testing of vertical so I could blow through it.

One last thing to note: it seems to have happened at least 2 of the 3 times with the A/C on, hot ass weather, and a fuel tank about 3/8 full or so. My guess is that the fuel pressue increased in the tank and it was venting to the engine. The heat soak may have caused the solenoid to stick (or what happened in this video when he pulls it apart).

The first time this happened I had a P0506 codes (idle lower than expected) that set. The first time I was driving and pumped the gas pedal multiple times and got the engine to rev up without stalling in neutral. After it came back down it sputtered again, but I was able to move it to a parking spot under its own power. After cooling off for several hours it ran perfectly. Very intermittent......

I'm going to brush it's teeth and replace this part as a precaution.

 

[Campie]

Here's an interesting video for the same type of running condition.

I pulled the purge valve off mine and cycled it with 12v and it works fine. I tried heating it up with a heat gun to simulate a hot engine bay without any definitive failure. But, its not to say that engine vibration with a long heat soak could be the issue. Also the orientation horizontal vs my testing of vertical so I could blow through it.

One last thing to note: it seems to have happened at least 2 of the 3 times with the A/C on, hot ass weather, and a fuel tank about 3/8 full or so. My guess is that the fuel pressue increased in the tank and it was venting to the engine. The heat soak may have caused the solenoid to stick (or what happened in this video when he pulls it apart).

The first time this happened I had a P0506 codes (idle lower than expected) that set. The first time I was driving and pumped the gas pedal multiple times and got the engine to rev up without stalling in neutral. After it came back down it sputtered again, but I was able to move it to a parking spot under its own power. After cooling off for several hours it ran perfectly. Very intermittent......

I'm going to brush it's teeth and replace this part as a precaution.

Cool stuff! For our issue, I replaced that purge valve and also the MAF but that didn’t fix the problem. Those items did increase the MPG from 12 to over 16 so there was a big bonus. Of course, towing is still 8 or 10 mpg, but from what I understand, that is expected. Our camper is only 17 feet but it’s a little over 10 feet tall and full 8 feet wide so it’s a pretty big parachute… the car pulls it really well, but when the engine compartment gets too hot, it just can’t keep up. We need to replace the fuel relay and the crankshaft sensor for sure because of codes thrown. We will also get the radiator and tranny cooler checked out.

Question: at 156,000 miles is it normal to replace the oil pump? Oil pressure is 50 cold and 18 or 20 hot. I know that’s low, but we haven’t replaced the O-ring on the pickup tube. With no lift, we’re gonna have to pay for that to be done. So, while the suspension is out of the way and the pan is dropped, I’m guessing an oil pump is the cost-effective way to go?

Before we do that though I’m thinking we should change out the oil pressure sensor and ditch the screen. Thinking I can probably do that in the driveway without too much trouble?

What are thoughts on ditching the screen in front of the oil pressure sensor?

 

[SpareParts]

Are you sure you have a screen? I believe 2007 did not have a screen as it did not have dod,, so no need for a screen

 

[donjetman]

Question: at 156,000 miles is it normal to replace the oil pump? Oil pressure is 50 cold and 18 or 20 hot. I know that’s low,

No, it's not normal to replace the oil pump. Your oil pressure is normal, not low.

To change the oil pump the timing cover must come off.

but we haven’t replaced the O-ring on the pickup tube. With no lift, we’re gonna have to pay for that to be done. So, while the suspension is out of the way and the pan is dropped, I’m guessing an oil pump is the cost-effective way to go?

What are thoughts on ditching the screen in front of the oil pressure sensor?

Replace the o-ring. I've used Felpro# 72401 and Mahle# B32790 on our 07 6.2L L92.

 

[B-train]

Cool stuff! For our issue, I replaced that purge valve and also the MAF but that didn’t fix the problem. Those items did increase the MPG from 12 to over 16 so there was a big bonus. Of course, towing is still 8 or 10 mpg, but from what I understand, that is expected. Our camper is only 17 feet but it’s a little over 10 feet tall and full 8 feet wide so it’s a pretty big parachute… the car pulls it really well, but when the engine compartment gets too hot, it just can’t keep up. We need to replace the fuel relay and the crankshaft sensor for sure because of codes thrown. We will also get the radiator and tranny cooler checked out.

Question: at 156,000 miles is it normal to replace the oil pump? Oil pressure is 50 cold and 18 or 20 hot. I know that’s low, but we haven’t replaced the O-ring on the pickup tube. With no lift, we’re gonna have to pay for that to be done. So, while the suspension is out of the way and the pan is dropped, I’m guessing an oil pump is the cost-effective way to go?

Before we do that though I’m thinking we should change out the oil pressure sensor and ditch the screen. Thinking I can probably do that in the driveway without too much trouble?

What are thoughts on ditching the screen in front of the oil pressure sensor?

I agree with @donjetman and @SpareParts . There was no screen for these trucks without AFM. At 156K, your oil pump is fine, they will last well over 200k with normal oil change intervals (I have a friend with a 2013 Denali with 276k, motor all original).

I will say this though for lower than normal oil pressure: replace the o-rings under the valley cover gasket. There are 8 o-rings under there that seal off oil passages that aren't used because of no AFM. They get hard and flat with age and will bleed off pressure into the valley, especially when hot and thin oil. Replace the oil pressue sensor when this is done with new OEM part.

I've done this on all the non AFM 6.2L motors I've owned over the years. It makes a big difference.

Keep me posted on what you eventually find the issue with dying to be. I'll have to check out the fuel pump relay on mine, but the way it acts, it seems like too much fuel, not losing fuel

 

[donjetman]

I replaced the o-rings/VLOM gasket last summer. This made no difference. Oil pressure remained normal like @Campie

 

[Campie]

I agree with @donjetman and @SpareParts . There was no screen for these trucks without AFM. At 156K, your oil pump is fine, they will last well over 200k with normal oil change intervals (I have a friend with a 2013 Denali with 276k, motor all original).

I will say this though for lower than normal oil pressure: replace the o-rings under the valley cover gasket. There are 8 o-rings under there that seal off oil passages that aren't used because of no AFM. They get hard and flat with age and will bleed off pressure into the valley, especially when hot and thin oil. Replace the oil pressue sensor when this is done with new OEM part.

I've done this on all the non AFM 6.2L motors I've owned over the years. It makes a big difference.

Keep me posted on what you eventually find the issue with dying to be. I'll have to check out the fuel pump relay on mine, but the way it acts, it seems like too much fuel, not losing fuel

Oh my, how hard is that to do? We’re not mechanics and we don’t have a lift!

Ok, so no oil pump yet, that’s good news!

Let me check the oil pressure, cold and hot again because I may have remembered wrong. I was pretty sure it was low, not horrible but definitely low. Thanks guys!