2009 GMC Acadia 3.6; Engine stall

2009 GMC Acadia 3.6 V6 AWD w/ high pressure fuel pump

Reaching out for some help on a problem with a car that has haunted me 3 other tech's.

This car has a spontaneous stall. It will start fine, and idle fine, and intermediately (no correlation between occurrence and time) stall. Sometimes it will be a short time after its started, sometimes it will take 1 min, 2 min, 3 min completely (seemingly) randomly.

If you start the car and hold the RPM around 2000 it will also 'stall'. To clarify it will almost appear as if you switch the key off, and then back on very quickly, except no dash lights go off and from my diagnosing no issue with ignition signal.

There are no DTC's stored an any of the control modules at all.

We have done the following shotty, shotgun/guesswork
Replaced the high pressure fuel pump
Replaced the throttle body
Replaced the crankshaft sensor
Replaced the engine wiring harness
Replaced the ECM
Reprogrammed w/ latest update all modules equipped
Tested fuel injectors with DMM
Replaced O2 sensor

I have spent hours looking at PID's and still have no clue where to go next. The only thing I have noticed to what I can not figure out is when the concern happens the ENGINE SPEED SENSOR will read 0. So it will go from 2000+ RPM to 0 and then in the next frame jump back to 1000+ rpm. The crankshaft position sensor does not drop out nor do any of the camshaft position sensors.

The engine does smell as though it is running rich, although the fuel is not commanding any rich or lean trims.

Well that's my story, hope someone can help; this car has driven me and 3 other guys near insanity. :huh:

have you checked to see if your losing a power feed to the engine control module?

how long is it until it can restart after stalling?

The PID, I believe named "Module voltage" never drops out. And if the engine is running it will record the "Engine speed" drop from 2000 to 0 them back up but nothing else seems to drop off completely but rather respond to the studder.

If it does stall completely dead from say a sitting idle in park, it will start back up right away in a ordinary operation, aside from a very rich exhaust smell.

Hey RCPro! I know from talking to other techs that these engines are known for the ignition coils failing, carrying secondary voltage back up to the PCM through the coil trigger wire. It usually ends up causing the coil to melt, but I've heard of it manifesting in other ways. This is a TSB detailing the problem:



FYI, the whole TSB is seven pages long. I had to shorten it to three so I could post it here. Let me know if you need the whole thing, and I can email it to you.

Would it be possible to watch the ignition coil current ramps, along with a coil trigger sync signal? The idea here would be to watch to see which coil fires right before the stutter/stall. If you can reproduce the symptom multiple times, and observe the same coil firing right before the problem, then I'd zero in on that coil.

After testing the coils and circuits and not seeing anything change from comparison to each other I decided to just replace all the coils anyways. Symptoms remain the same. After replacing the coils the car started and stalled shortly after 2 times. Started and ran for a min or so, and then started and ran for aprox 3 min before I decided to pull it out and try and drive it. Stalled before I backed out of the service shop. Still a very rich smell from the exhaust, still no engine codes.

I also tried unplugging the crank sensor and running it off of just the cam sensor. The same symptoms persisted. I checked the ignition switch for voltage drops or abnormality and nothing as well.

This car continues to perplex me. My gut instinct makes me think that for some reason the entire system is restarting for no known reason. As if you were very quickly turning the key of and back on while its running.

I have also replaced the engine fuse box. Usually I am very anti-parts-changer on things, but this specific diagnosis has the entire shop swarming. Any further direction is appreciated!

Have you tried monitoring the power coming out of the ignition with a scope or some other fast meter during the stall event to be sure it's not momentarily dropping voltage?
I know you said the module voltage data PID doesn't change, but a voltage measurement to back that up wouldn't hurt in my opinion.

What is the motor actually losing to make it stall? Can you current ramp the coils and injectors and see? Then like Noah said, watch the power supplies.


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Checked all power and ground to PCM using Modis Ultra on a 20v x 2sec graph
Pins: 76, 77 on connector X1
Pins: 1,2,3,4,5,6,54 on connector X2

When engine is revving 2000 rpm and motor attempts to stall there is little to no voltage drop.
When engine is at idle and stalls it goes from charging voltage (14.5v~) to battery voltage (12v~)

I may have found something to point us in a direction. The following pictures (sorry my modis didnt wanna upload..) are graphs of the injectors. When the symptom occurs I have noticed that injector 1 seems to be missing.

The picture with the note HV,
Green is circuit 4904 Direct Fuel Injector High Voltage Cylinder 4
Yellow is circuit 4901 Direct Fuel Injector High Voltage Cylinder 1

Note labeled HV Control is backprobed at the same connector
Green is circuit 4804 Direct Fuel Injector Control Cylinder 4
Yellow is circuit 4801 Direct Fuel Injector Control Cylinder 1

Finally the coil trigger backprobed at the ECM
Green is circuit 2124 IC Control Cylinder 4
Yellow is circuit 2121 IC Control Cylinder 1

Nice captures. In that last capture, it appears that #4 got skipped once, and #1 got skipped twice? It's like the PCM just gave up control momentarily...

Does the vehicle have to be moving to get the stall? Wondering if there's some kind of torque limiting strategy at work.

It does it both stationary and in motion. I do think that there is a torque limiting feature built in to one of the modules, I remember reading a TSB about a customer complaint that the service advisers were told its a programmed condition.

Maybe I should boot into the transmission side of the parameters and poke around in the speed sensors or limiting feature PID?

Weird for sure...
But on the plus side it's easily repeatable!
Is it stalling after the transition from open loop to closed loop?

The other thing I was thinking that's kind of a shot in the dark is to monitor the 5v ref circuit during the stall at the PCM. I imagine that a ref circuit problem would
a) set a code, and
b) cause at least a momentary no comm.

Not sure why this isn't setting any codes in any modules either. No pending codes either?
Checking Global OBD and Manufacturer specific? Not nit picking here, just trying to cover the bases.

The stalling isn't related to the fuel loop I questioned that myself. No codes what-so-ever pending or active in any modules manufacture specific as checked with my Modis and the Maxisys.

I did all the guided test on my Modis with all four cam position sensors and cam actuators just for something to do I guess.

I will test the reference circuit when I get back to the shop but I recall checking it I believe. I'll have to double check to be sure, losing track of all the tests I've done

How about Global OBD for codes or data that may appear out of place which could be masked in Manufacturer mode?

Hmm thats interesting I've never considered that circumstance. I'll check that as well tomorrow morning when I return. I don't normally go into that mode, the normal Maxisys 'Auto Scan' feature does runs through all the modules and pulls the codes. Same with the Modis.


Thanks for all the help, it's really appreciated. Surely something is gonna prove broken right?

An observation i made when looking all over this engine, it appears as though both cylinder heads have been replaced. The reason I say this is because they look very very new. On a SUV with ~70,000 I can't imagaine they would look so differently then the block.

I did replace cylinder #1 fuel injector. It seems as though because of the high pressure fuel system. These injectors are opened with a quick pulse of~64 volts via a ECU driver and then maintained by 12v.

Now when you first start this care the knock sensors go from 64v down to around 7v or so if I remember correctly. Now I had a hunch that maybe the 64v from the injector was grounding to the head, and then transferring to the block and somehow back through the voltage sensor for the knock sensor. Probably a bunch of non-sense but I'm am starting to wonder if I should find a good exorcist for this car's ghost.. Jokes aside it must be some kind of reading fluke, because I happen to have another car (same year, miles, fuel system, ect) I have been comparing it too; it to starts at a knock sensor reading for 60v+ and goes down progressively as the car is ran.

Food for thought. Asked the boss for a break from working on Volkswagen and this is what I get.

RCPro wrote: Asked the boss for a break from working on Volkswagen and this is what I get.

Your boss is just plain MEAN. :lol:

I like the idea of going into the transmission and looking for data that stands out. Trying to think of all the reasons the ECM would shut the engine off with no codes... How about alternator ripple? Or, maybe try running it with the field connector unplugged. Reaching, I know.

New heads? I would have suggested checking grounds, but you already went over that. Timing? You'd think it'd set a code...

Checked for any codes under global setting in my Modis, noting turned up.

Rooted around in the Transmission PID's and may have found something. When the symptom occurs "Shift Solenoid 2" that is normally commanded on when the engine is running, turns off briefly, and when the engine returns to normal operation it is back on. Another PID "Shift Solenoid 2 CKT Status" goes from "Ok" too "Intermediate".

RCPro wrote: Checked for any codes under global setting in my Modis, noting turned up.

Rooted around in the Transmission PID's and may have found something. When the symptom occurs "Shift Solenoid 2" that is normally commanded on when the engine is running, turns off briefly, and when the engine returns to normal operation it is back on. Another PID "Shift Solenoid 2 CKT Status" goes from "Ok" too "Intermediate".

I like it! Maybe unplug the trans connector and see if it stays running? If you're lucky, it'll default to 3rd gear or something, and you can even take it for a drive. :silly:

Ended up dropping the entire power train from the Acadia and swapping it with one from a wreck. Never had the problem come back. Still don't know what was causing the issue but I think about this car at least once a week. One of the few that got away from me.