Truck stalled while leaving parking lot. What may have caused this?

[testdepth]

2012 Yukon Denali 6.2L 6L80E 171000 miles.

I have been driving this truck for over a week with no problems at all. Wife drove it 40 miles one way with no problems. On her way back after driving about 10 miles she stopped at a store. She started the truck and backed out of the parking spot and pulled slowly forward when the truck stalled. No prior indication of a problem or about to be one. She immediately tried to restart and the engine cranked multiple times but no start. She let it sit a few minutes and it fired back up so she drove it the rest of the way home without any more problems. I put my bidirectional scanner on it and nothing. No check engine, no current DTCs, no misfires and fuel pressure of 43psi on this FLEX engine truck.

Any ideas what would cause this?

 

[Doubeleive]

I have been driving this truck for over a week with no problems at all. Wife drove it 40 miles one way with no problems. On her way back after driving about 10 miles she stopped at a store. She started the truck and backed out of the parking spot and pulled slowly forward when the truck stalled. She immediately tried to restart and the engine cranked multiple times but no start. She let it sit a few minutes and it fired back up so she drove it the rest of the way home without any more problems. I put my bidirectional scanner on it and nothing. No check engine and no current DTCs.

Any ideas what would cause this?

all anyone can do is guess and throwing parts at it is not always a wise choice
that being said you could start with some basics like monitoring fuel pressure.
what maintenance has been done and at when at what mileage?

 

[Joseph Garcia]

As @Doubeleive suggested, start by monitoring the fuel pressure. You stated that you have a bi-directional scanner, so you should be able to do this quite easily. Let's confirm or reject the suggestion that your issue may be related to fuel pressure, as the symptoms that you describe would point in that direction as the source of you issue.

 

[mikez71]

Unfortunately, you'll have to wait for it to act up again to catch it..

There is a fuel pump trim, see what that number looks like. @swathdiver mentioned it a few times, and it *maybe* some indication of pump health.
(I'm just asking you to check because I'm curious )

 

[testdepth]

I placed a fuel pressure gauge on this truck and it tested at 43psi at idle. I'm told that's normal for a FLEX fuel engine. All last week this truck drove just fine every day. Yesterday after sitting all night it was driven about 50 miles with no problem. My wife parked and went inside a store. When she came out and went to pull away from her parking spot it stalled in the parking lot. Today this happens: Truck sat all night and this morning my wife gets in to drive to the store. She gets about 2 miles from home (speed is 45 to 50) and stops at a light. She sat idling in Drive no problem. The light turned green so she gave it gas to go and the truck surged about 4 times but did not stall so she pulled over. She sat there running but in park. The truck didn't stumble and no check engine light so she sat there running. After a few minutes she put it in drive and went to the store with no more problem. She left that store and went to another one and parked. She left this store and then came back home with no more problems.

Truck surged 4 times and then worked fine the rest of the drive. No check engine lights and no DTCs. I don't get it??

 

[j91z28d1]

going to be a hard one to find unless you get lucky and have a scanner looking at live data while it's doing it. and then you have to now that to look for.

hard to say just throw parts at it, because replacement part quality is so low these days. anything you replace, keep the old one as a back up or test.


common issues around here for weird things are battery cables/terminals. they look fine, but go bad inside. terminals being loose. you need to be very tight, like can't twist them at all with 2 hands. battery itself being low, over 5 years old. even a bad evap purge valve can open at the wrong time and flood the engine with fuel. does it give you a hard time filling the tank at the pump? like pump clicks off as if the tank is full but it's not? that's common too. you see that watching the o2. sensor voltage go dead rich when it's stalling or bucking.

MAF sensor needing cleaning or replaced. throttle body being worn out. it's got a electric motor and gears in there with 2 position sensors. they get sloppy. but those last 2 usually throw codes after a while. but not always at first.

the fuel pressure gauge is a good test, but you gotta be looking at it as it stalls or acts up real time.
tons of other stuff, bad ground points seem common if you're up north in the salt.

always the worst when it's the wife that's out diving around with them acting up and you're not sure what it is. good luck.

 

[testdepth]

I tested fuel pressure and fuel trim at idle and at 2000rpm:
FUEL TRIMS: Look normal and so do the O2 sensors.

IDLE
STFT BK 1 0 to 6
STFT BK 2 0 to 6
LTFT BK 1 1
LTFT BK 2 1

2000 RPM
STFT BK 1 -3 to 2
STFT BK 2 -3 to 2
LTFT BK 1 0
LTFT BK 2 1

Fuel pressure shown on scan tool is 43psi whether at idle or 2000rpm.

O2 SENSOR BK 1 SENSOR 1 constantly jumping from 70 to 800
O2 SENSOR BK 2 SENSOR 1 constantly jumping from 100 to 815

 

[testdepth]

going to be a hard one to find unless you get lucky and have a scanner looking at live data while it's doing it. and then you have to now that to look for.

hard to say just throw parts at it, because replacement part quality is so low these days. anything you replace, keep the old one as a back up or test.


common issues around here for weird things are battery cables/terminals. they look fine, but go bad inside. terminals being loose. you need to be very tight, like can't twist them at all with 2 hands. battery itself being low, over 5 years old. even a bad evap purge valve can open at the wrong time and flood the engine with fuel. does it give you a hard time filling the tank at the pump? like pump clicks off as if the tank is full but it's not? that's common too. you see that watching the o2. sensor voltage go dead rich when it's stalling or bucking.

MAF sensor needing cleaning or replaced. throttle body being worn out. it's got a electric motor and gears in there with 2 position sensors. they get sloppy. but those last 2 usually throw codes after a while. but not always at first.

the fuel pressure gauge is a good test, but you gotta be looking at it as it stalls or acts up real time.
tons of other stuff, bad ground points seem common if you're up north in the salt.

always the worst when it's the wife that's out diving around with them acting up and you're not sure what it is. good luck.

@j91z28d1 replying to your thoughts and thank you for the input. I installed a brand new OEM negative battery cable set and cleaned all connections. No issues filling the tank and I did replace the EVAP purge solenoid and tested it good. MAF sensor is bran new and looks to be working normally on scan tool. Throttle body is brand new and did the relearn. I disconnected, cleaned and reconnected the grounds I could find in the engine bay and under driver's door. This truck has always been a southern truck and has no rust under it. All four O2 sensors are original 171000 miles. Any ideas are helpful. Thank you. Each time this happens there is no check engine or DTCs.

Truck has 171000 miles and is 13yrs old and I've been having problems with it that are random. Drive for 10 days with no problem and then problems start with surging while driving at speed under 50 or it stalls out like a few days ago. Then last week it drove fine all week. Then the recent stall and surging started. In the last month I've changed:
Iridium plugs, coils, throttle body, crank sensor, coolant sensor, fuel injection sensor, negative battery cables, valve cover gaskets, motor mounts, MAF sensor, Fuel pump w/ fuel pressure sensor tested fuel pressure at 43psi. I even tested the transmission pressures in this 6L80E and they were normal with dirty fluid. I went out there while it was idling and pulled on wires all over the engine bay trying to get it to surge or stumble but nothing happened. I also installed an AFM disable but these recent problems happened with it installed. It's a real PIA!

 

[mikez71]

You would need to test fuel pressure when it doesn't run to see if the pump or something related died.
But there is a fuel PUMP trim, separate from fuel trims, that should be found in the Fuel System Control Module.

Maybe crank sensor starting to go out, preventing injection? (NVM, I see you done did that...)

 

[j91z28d1]

@j91z28d1 replying to your thoughts and thank you for the input. I installed a brand new OEM negative battery cable set and cleaned all connections. No issues filling the tank and I did replace the EVAP purge solenoid and tested it good. MAF sensor is bran new and looks to be working normally on scan tool. Throttle body is brand new and did the relearn. I disconnected, cleaned and reconnected the grounds I could find in the engine bay and under driver's door. This truck has always been a southern truck and has no rust under it. All four O2 sensors are original 171000 miles. Any ideas are helpful. Thank you. Each time this happens there is no check engine or DTCs.

Truck has 171000 miles and is 13yrs old and I've been having problems with it that are random. Drive for 10 days with no problem and then problems start with surging while driving at speed under 50 or it stalls out like a few days ago. Then last week it drove fine all week. Then the recent stall and surging started. In the last month I've changed:
Iridium plugs, coils, throttle body, crank sensor, coolant sensor, fuel injection sensor, negative battery cables, valve cover gaskets, motor mounts, MAF sensor, Fuel pump w/ fuel pressure sensor tested fuel pressure at 43psi. I even tested the transmission pressures in this 6L80E and they were normal with dirty fluid. I went out there while it was idling and pulled on wires all over the engine bay trying to get it to surge or stumble but nothing happened. I also installed an AFM disable but these recent problems happened with it installed. It's a real PIA!

that's a lot of new parts. all this was after the truck started acting up randomly?

but yeah, I agree with @mikez71. you'll have to be actively watching or logging while it's freaking out.

 

[Fless]

After replacing a crank sensor a CASE relearn should be done, in case that was missed. Be aware that aftermarket crank and MAF sensors don't always play well with these engines.

 

[testdepth]

After replacing a crank sensor a CASE relearn should be done, in case that was missed. Be aware that aftermarket crank and MAF sensors don't always play well with these engines.

@Fless Yes Sir I used my scan tool to perform the relearn after replacing the crank sensor.

 

[Doubeleive]

probably just going to have to do a drive record and see if anything rears it's head.
curious when this happens is it just the engine? or is all power lost?
if it is just the engine what do the gauges show? like voltage?, temp?
also when it dies and before you cycle the key or whatever happens, try scanning it then
also see what the key position shows with the scanner before you touch anything.
intermittent problems suck but something should be detectable it's just a matter of looking in the right place under the right conditions.
keep the fuel pressure gauge on it while driving around, you can stick it up under the hood so you can see what it shows at all times.

 

[SpareParts]

Did the problem start after you installed the AFM disable?

 

[Joseph Garcia]

You've stated that you tested/measured the fuel pressure at various RPM's. Have you left this pressure test gauge on/attached and monitoring fuel pressure as you drive? In other words, can you observe the fuel pressure at the actual time that this event is occurring? I know that the occurrences are random, but if the gauge is in place always while running, you may be able to observe when the event suddenly occurs.

 

[testdepth]

Did the problem start after you installed the AFM disable?

@SpareParts No Sir the problems with this truck started before I installed the AFM disable. The AFM disable install was an attempt to isolate this problem by preventing the engine from shifting back and forth from 8cyl to 4cyl at low speeds where I'm having this surging problem. But then it happened while AFM disable was installed.

 

[testdepth]

You've stated that you tested/measured the fuel pressure at various RPM's. Have you left this pressure test gauge on/attached and monitoring fuel pressure as you drive? In other words, can you observe the fuel pressure at the actual time that this event is occurring? I know that the occurrences are random, but if the gauge is in place always while running, you may be able to observe when the event suddenly occurs.

@Joseph Garcia I tested the pressure while sitting in my driveway and not driving around. The pressure in park and turn the key to on but not start is 58 (prime). The pressure when the key is turned to start in park goes up to 60 and then as idle drops to normal 600rpm the pressure is 43psi. While running at idle and 43psi I then increase rpm slowly up to 3000 rpm and the fuel pressure stays at 43psi the entire time. It never once dips either while cold or at normal temp.

I have not connected the gauge and drove around or connected my scan tool and drove around monitoring fuel pressure.

 

[testdepth]

probably just going to have to do a drive record and see if anything rears it's head.
curious when this happens is it just the engine? or is all power lost?
if it is just the engine what do the gauges show? like voltage?, temp?
also when it dies and before you cycle the key or whatever happens, try scanning it then
also see what the key position shows with the scanner before you touch anything.
intermittent problems suck but something should be detectable it's just a matter of looking in the right place under the right conditions.
keep the fuel pressure gauge on it while driving around, you can stick it up under the hood so you can see what it shows at all times.

@Doubeleive First we all have to remember this truck is my wife's 99.9% she is driving it and what she sees and tells me won't be as thorough as what we would see and look for. This time when this truck stalled on her in the parking lot it sounds very much like when my Dodge Ram 5.7 1500 stalls randomly. Like my truck she was at low speed and made a left turn when it stalled out. She attempted to restart but the engine just cranked with no start so she let it sit a few minutes more and it fired right up and no more problems the rest of the day. My Dodge will do the exact same thing randomly. I think this stall was a one off and not related to the other problems with this Denali.

 

[Doubeleive]

@Doubeleive First we all have to remember this truck is my wife's 99.9% she is driving it and what she sees and tells me won't be as thorough as what we would see and look for. This time when this truck stalled on her in the parking lot it sounds very much like when my Dodge Ram 5.7 1500 stalls randomly. Like my truck she was at low speed and made a left turn when it stalled out. She attempted to restart but the engine just cranked with no start so she let it sit a few minutes more and it fired right up and no more problems the rest of the day. My Dodge will do the exact same thing randomly. I think this stall was a one off and not related to the other problems with this Denali.

ok, but a good working GM suv should never stall basically ever.... if it does then something is wrong, the only time it is acceptable is if it ran out of gas.
if it idled down and died due to power steering requesting a little bit of hp then the maf/throttle body/ambient temp reading should be looked at, run some injector cleaner in it for the meantime, that can help sometimes. Optionally a injector service runs about a $100 unless you buy the kit and diy.
at 171k it should be done for sure regardless.

 

[testdepth]

Is it normal for the fuel pressure sensor values to go up and down. I connected my scanner and recorded the pressure requested, pressure sensor voltage and pressure sensor pressure while driving. While cold 57 here this morning and before the truck was warm the values were up and down from 39.5psi to 45.6psi and fluctuated up and down while pressure requested remained at 43psi and the voltage stayed at 2.29 volts. The only thing fluctuating was pressure sensor.

This fuel pump came with a new sensor and it is an AC Delco pump I installed a month ago.