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Infrequent stalling during warm up
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2010esv
Novice
Jan 21, 2024, 12:25 PM
Post #1 of 9
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Infrequent stalling during warm up
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2010 escalade 110K miles
I have an infrequent issue that occurs during warm up period after cold soak about the time that the temp needle starts moving. Engine rpm drops and surges to rebound several times. Sometimes it is subtle and other times its enough to stall the engine. After the event the truck runs fine and there are no codes stored, lights, CEL, etc. No loss of electrical power noted during the event as well. Sometimes happens a few times a week and other times goes months in between occurrences. This has been going on for a year or so and a mechanic was unable to find anything wrong or reproduce the issue.
On my own I was able to capture some data via ODB logging. Around or during the event:
fuel trim cuts hard both banks
upstream 02 stops oscillating and pegs rich around 0.9V both sensors for a few seconds
downstream jumps from .7V to .9V both sensors for a few seconds
fuel pressure looks good. KOEO, idle, and running in spec as measured with gage and reported via obd
Air flow and fuel flow rates look goodoil pressure good
manifold pressue as recorded doesnt reveal vacuum leak
no codes, lights, cel, etc
no correlation to temp, humidity, etc
things performed before issue:
plugs and wires replaced about a year prior
dropped tank and cleaned carbon pellets out of evap line. replaced, evap can, vent valve and purge valve to address issue with fuel fill up.
new alternator, water pump, belts, pullies, and tensioner as preventative maintenance
cleaned TB and MAF
performed after issue started:
dropped tank again and re-cleaned fuel evap lines and replaced purge valve because i didnt do a great job the first time
Always 93 octane gas and tried multiple tanks of fuel cleaner
new battery
battery posts cleaned and dressed multiple times during trouble shooting
ground points checked and measured
all 02 sensors replaced - no change
tps replaced - no change
throttle body and tps replaced - no change
maf cleaned with correct cleaner multiple times
oil/filter, air filter, and other regular maintenance as needed
looking for help, ideas, experiences, etc.
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Hammer Time
Ultimate Carjunky
/ Moderator
Jan 21, 2024, 2:13 PM
Post #2 of 9
(20081 views)
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Re: Infrequent stalling during warm up
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It sounds like you've been pretty thorough with this.
The only thing that comes to mind is possibly the ECT has a bad wire or connection and is going open circuit intermittently although I would expect that to set a code. That would prompt the PCM to go full rich.
The only other possibility I can see is maybe the PCM is momentarily glitching. The fact that all sensors make major moves suddenly does seem to point to a PCM glitch if it's not a ground issue which you said you checked.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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2010esv
Novice
Jan 21, 2024, 3:54 PM
Post #3 of 9
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Re: Infrequent stalling during warm up
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Thanks for responding
What is interesting is that IF it does happen it happens only about 5-10 min after start up right before the DIC shows the coolant temp in its warm state. I had it drive great in the AM and then freak out on my drive after work as well as the opposite. I would think that if it was a failing sensor, SW glitch, or a cut/loose wire it would happen at other times. What should i do to verify ECT working properly? If it is the ECM would that require a FW flash or reprogramming to fix?
If there is air in the coolant system would that cause the ECT to bug out? Might be something with air collecting behind the tstat and then as it opens up hits the sensor. Not sure why that would cause the truck to push rich and then pull back though.
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Hammer Time
Ultimate Carjunky
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Jan 21, 2024, 4:15 PM
Post #4 of 9
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Re: Infrequent stalling during warm up
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No, air's not the problem. That would only drop the temp 10 or 20 degrees. Open circuit on the sensor would drop the temp signal to -40.
It appears to be happening about the time the PCM goes into closed loop. That could mean one of the sensors that is being ignored in open loop, suddenly becomes a player with corrupted info.
I think it's going to take a lot of monitoring with a scan tool to try to look for something that suddenly changes that could account for the problem.
No, I don't think it's a flashing problem. If the PCM is to blame, it's would be because it is having a sudden brain fart from an internal or wiring failure.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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2010esv
Novice
Jan 22, 2024, 6:22 AM
Post #5 of 9
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Re: Infrequent stalling during warm up
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It re-occurred this morning on my way to work but not bad enough to stall out.
Same result with 02 up/down sensors and fuel trim.
No issues seen with coolant temp response. I did record timing advance but figure that is more of a reaction to the event then the cause. Fuel pressure ok, MAF responding, etc
One thing that did stand out is the event occurred right as the evap system vapor pressure dropped. The vapor pressure is hanging around 0 +/- 100 Pa, then quickly drops to -2500Pa and rebounds back to about 150Pa. I thought that this was normal as the ecu purges vapor from the system but could account for why the 02 goes rich and the ecu pulls fuel trim.
The evap canister, purge and valve are all newer however could there be a fault resulting in too much fuel vapor causing a control issue? Or alternatively would a sensor be a fault that results in an incorrect a/f ratio that takes a few seconds to a min to resolve?
(This post was edited by 2010esv on Jan 22, 2024, 6:56 AM)
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Hammer Time
Ultimate Carjunky
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Jan 22, 2024, 7:19 AM
Post #6 of 9
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Re: Infrequent stalling during warm up
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If you think that is a possibility just disable the Purge valve and see if the problem goes away. I would probably just plug the vacuum line if that is possible as opposed to unplugging the electrical connector which will set a code.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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2010esv
Novice
Jan 23, 2024, 2:43 PM
Post #7 of 9
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Re: Infrequent stalling during warm up
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Truck drove great with the purge valve electrically disconnected. It will be a while before i can drop the tank again so i am left trying to speculate.
Would a stall be possible if the vent valve is stuck open and the ecu triggers purge?
Would a stall be possible if the lines are clogged and no vapor can make it to the engine when a purge is commanded?
Any other ideas or starting points?
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Hammer Time
Ultimate Carjunky
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Jan 23, 2024, 2:57 PM
Post #8 of 9
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Re: Infrequent stalling during warm up
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I don't know what dropping the tank has to do with the purge valve. The purge valve just opens to allow fumes from the tank into the intake of the engine to be reburned.
The valve is programmed to open at specific times and I suppose opening at the wrong time could trigger stalling. You might also want to check the charcoal canister to make sure it's not saturated with raw fuel because someone previously overfilled the tank.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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2010esv
Novice
Jan 23, 2024, 3:57 PM
Post #9 of 9
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Re: Infrequent stalling during warm up
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dropping the tank would be to get access to all the evap lines to check for clogs or leaks. I assuming that disconnecting the purge valve just isolates the problem to something within the evap circuit; vent, purge, canister, or lines.
no fuel in canister from what i can tell.
I know the purge valve is OK because i have tried a few during the process with no change or resolution. Regarding if it is opening at the wrong time, what do I do about that?
(This post was edited by 2010esv on Jan 23, 2024, 4:13 PM)
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