2010 GMC Acadia Start Stall, Crank No Start, Popping into intake

Brian Owner/Technician Ohio Posted   Latest  
Discussion
Driveability
2010 GMC Acadia SLT 3.6L (D LLT) 6-spd (6T75)
Crank / No Start
Start-Stalling

We had a 2010 Acadia come in with symptoms of timing chains. Customer shut it down one night, and went to start it next morning and it was a no start. Not sure how long it was cranked on. When it got to the shop in was a start stall while popping in through the intake, and at times Crank No Start. Look over scan data quickly with no directions, Temps,Pressures ECT. I believe O2 sensor for codes. Went to performing a Relative Compression test which was also heard and it showed one bank lower that the other​.​Plugged in and performed CMP, CKP correlations. Compared with known good, decided they was good.

Before going in cylinder i quickly looked at Relative compression again and this time noticed my coil wasn't firing as soon as engine started cranking. That made me look at the CMP & CKP a little closer. Looked at Falling Edge count and found noise that looked to be a bad input to the ECM. Replaced the CKP sensor with no change. At this point i realized i made the wrong call most likely off of noise in my waveform Grounding off the block instead of a cleaner location. 

I move on to In cylinder of both banks, even with the unknowns of the coil firing, which did show a difference of overall compression and off some on valve timing from a known good, but even not having alot of training in in cyl testing, I didn't fill it wound be off enough to cause my problem. It should run.

At this point the engine would sometimes stay running longer than before, but pop really bad. I wanted to see what the Injectors was doing, so i done a injector balance using GDS2 and after two separate test showed the injector flow was all over the place from one to another. I also wanted to see the WORK being done with a amperage waveform, and here is where i set myself back even more. Tested one injector on both banks. One showed twist as many firing events as the other bank. Now i have had the coils not firing from the start, and now a bank of injectors firing too much.

Very confused i now again start looking at inputs again, SI, TSB's ect and found a tsb that talked about Dual Pulse Injector Strategy to help warm up the cats and decrease the time of fuel control, which only once per key cycle. Had never heard of that. It only happens once per key cycle and the engine had stalled, then i performed the same on the other bank and it was back to signal firing. So at this point im hours into it and can't make a call, i decided of instead of relying on fuel pressure from scan data i need to look at it with a gauge. 

Any time i hook a fuel pressure gauge up i always take a sample of fuel. And WOW, a load of water. I pumped the tank, removed and replaced the injector due to the mileage, water AND i had them out already. I wouldn't know if the balance test was result of the water or injectors.

I know there will be some that would have took a completely different approach to this, and I myself will next time too. Im still not sure of why the coils was slow to fire during cranking that if someone could shed light on it would be great. I can only assume the Relative compression was a effect of cylinder wash. I continue to try to improve the speed of Diagnosing so am open to here from everyone that is willing . AND its my first time doing a write up, so go easy lol. Also keep in mind to, This Vehicle was a while back, so im writing this as i remember it. So Sorry if it doesn't make complete since step by step.

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Dave Mobile Technician
Ohio
Dave Default
 

Good job, Brian. Don't beat yourself up because of the time spent testing. The main thing is that you did the testing many would not have and would have just fired the parts cannon at it. Water in the fuel is not a very common problem and not the first thing we think of.

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Mike Educator
North Carolina
Mike Default
 

Good find. Llike Dave said, don't beat yourself up. I have always felt like there are no wasted tests. They either prove something is good or they prove something is bad, either way you have more data than before. The main thing is that you stuck with it and found the problem instead of throwing part after part after part at it.

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Stuart Mobile Technician
Illinois
Stuart Default
 

Good call and thanks for sharing​.​Also,quit beating yourself up over the time spent.I had a similar example last year with bad gas and the only way I found it was the smell.I guess that is why I was gifted with a big nose,after many tests such as you went through nothing smelled right​.​The fuel or the exhaust just didn't smell right.I tested the fuel and was water…

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Tim Owner/Technician
Virginia
Tim Default
 

Good job. Thanks for posting, we all miss things but you didn't give up or throw a bunch of parts at the vehicle.

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Craig Technical Support Specialist
Illinois
Craig Default
 

Brian, thanks for the write up, I think it would be safe to say almost everyone has played with the contaminated fuel gremlins. The post reminds all of us that persistence and determination can solve many problems. As others have said it's better to test and disprove, than start hanging parts. Plus another thanks for the known good patterns, I am starting to see a lot of these GM 3.6 motors…

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Brian Owner/Technician
Ohio
Brian Default
 

Thanks man, If you need any more known goods for this engine just hit me up.

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Brian Owner/Technician
Ohio
Brian Default
 

Thanks everyone for your support. I also wanted to make a correction to. As i read back over my post i noticed i said i was using GDS2. It was my Tech2 as GDS2 isn't supported on this vehicle. Before someone caught that. Again this was a few jobs ago.

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Firas Owner/Technician
California
Firas Default
 

Thank you for the information

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Rudy Technician
California
Rudy Default
 

Brian_ My only input here is to say dont worry about speeding up your diagnosis and just worry about being as thorough as possible. The speed will come naturally.

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Richard Technician
New York
Richard Default
 

Great job, contaminated fuel can be the trickiest thing to diagnose. Because it is very rare, at least around me, and you still have pressure. At least you took a fuel sample and looked at it. The very few times I have had bad fuel I skipped that test and spent another hour going in circles.

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Thanks