2011 GMC Acadia weirdness - ROUND 2... FIGHT

Yeah I noticed the first scan log was a good bit worse on #6 but didn't run long enough to show anything on #4. Was that one taken prior to warrantying out the injectors or swapping ignition components?

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Yeah I noticed the first scan log was a good bit worse on #6 but didn't run long enough to show anything on #4. Was that one taken prior to warrantying out the injectors or swapping ignition components?
 

All data and scope captures are after moving the coils and changing the injectors.

So crankcase pulses during #3 and #6 compression... I didn't leak down test #3, but #6 had less than 5% when I tested it last week. I think I'll pull the intake off (again) and compression/leak down all cylinders. And borescope all cylinders, just for giggles.

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 I think I'll pull the intake off (again) and compression/leak down all cylinders. And borescope all cylinders, just for giggles.

 

I'd like to see Cranking Compression on all cylinders. (I'd REALLY like to see Running Compression, on all cylinders. But,....)

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Hmmm...

I am, still, seeing #4 as the lowest contributor. But, looking at the Crank Case pressure, I would expect to see a repetition of 6 pressure events. I see two. I see pressure spike #6 compression, and #3 compression.

 

The #6 spike drops off before TDC. The #3 spike extends past TDC which makes me wonder if #4 is also contributing to it??

 

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 The #6 spike drops off before TDC. The #3 spike extends past TDC which makes me wonder if #4 is also contributing to it??

 

I suspect the same thing.  Hey, Tyler. When doing cranking compression, grab crank case, too.
 

We need to have a live video chat going when I do this stuff. :silly:

 

Emailed Chad the cranking compression capture. PV350 in the cylinders, intake off, injectors unplugged. Did it in the reverse of the firing order, so I might catch whatever is wrong with #6 and #4 sooner. Readings are in kPa, so you'll need to do the math for freedom units.

Rough measurements put the very lowest clean tower (#6) at 158 PSI, and the very highest tower (#3) at 167 PSI. That's being pretty nitpicky. Not much of a spread, IMO.

 

Don't sweat the noise between cranking events - that's me handling the PV350 while swapping cylinders. Shout out to Juergen and his suggestion of externally grounding the PV350. Didn't get rid of the noise, but definitely took it down a notch.

Zoomed in on #6:

 

I do you have all the spark plugs pulled. I see a crank case pressure spike follow your in-cylinder.

 

The spike is not the same for each cylinder.

 

Yep, all plugs out. Are we looking at the higher initial pulse on the first tower of #6? 

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We need to have a live video chat going when I do this stuff. :silly:

 

 

Fire it up!
 

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Yep, all plugs out. Are we looking at the higher initial pulse on the first tower of #6? 
 

That is something to look at. I don't know what to make of it, though.  Is it repeatable? Besides that one, cyl #3 pushes into the crank the most. #2 the least.  I don't want to spend too much time barking up the wrong tree, but can you post a Cranking Crank-case, with all the plugs in, please?


 

Can do. I've got the plugs back in and intake back on. After your cranking waveform, I'm gonna run it again and set it up for Monday morning.

Cranking crankcase pressure in red, #6 trigger in blue, RC in green.

 

I think this is an ugly intake waveform, too. These are new heads, correct?

 

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I think this is an ugly intake waveform, too. These are new heads, correct?

 

 

The long block is a 'reman' from Midway.

I did eyeball the ports with the intake off. No significant buildup of anything.

Started it up again this morning. Only four miss counts. No codes set.

 

Caught it setting P0300/P0306 on Sunday. I got a little bit smarter and decided to watch HPFP angle during the cold start:

 

It's got the angle dialed up during the miss, then scales it back. Miss disappears. There's enough of a correlation there to make me suspect our issue is still fuel related.

I got desperate and put a request into the Identifix Hotline. The gentleman on the other end correctly pointed out a GM PI that I'd missed early on. :blush: PI1296.

 

Talks about the orientation of the injectors being incorrect after service. Well, we've had these rails off like, 20 times now. Sounds promising! Nope, they're correct. :silly: 

Calling this one fixed for now. If you're just passing through, looking to fix your misfiring Traverse/Acadia, here's the silver bullet version - I reflashed the PCM with the latest calibration.

Just about threw in the towel on this one. :blush: Got pretty desperate while looking for SOMETHING wrong with this engine. Found the injector TSB, it's all good. Thought maybe the pistons on one bank were installed backwards (the piston tops are asymmetric and faced towards the injector). Nope, they're fine.

Found PIP5528 which describes a misfire on #5 or #6 immediately after installing a reman engine. Wants you to check the 'ring strategy' to make sure the cam is correct for the application. Talked to the engine rebuilder directly. They assured us the camshafts were correct.

 

Boss asks if there's a newer calibration available. ...I dunno, maybe? :huh: I was so wrapped up in tracking down the misfire, I'd never stopped to look. I check GM TIS, and whadya know, there's an update! I slam it in and put it all back together. This was the second cold start after the reflash:

 

The engine feels like it's running the EXACT same way it did before. The reflash just turned the misfire sensitivity down during a cold start. This fix really isn't a fix, IMO. More like a patch for poor engineering.

In retrospect (which is always 20/20), there IS a TSB that points to this reflash:

 

I missed this one partly because there's a TON of TSB's/PI's for misfiring on this vehicle. Mostly because all the data pointed to a genuine misfire, exactly when the PCM said it was happening. Ultimately, I have no one but myself to blame for not finding this earlier.

This customer has vehicles in and out of our shop all the time, so I'll hear about it if this isn't a lasting fix.

Thanks for the feedback!

Another update for giggles. This one came back again... with a dead alternator. Voltage drops are solid, L and F-terminals are working. Belt didn't fall off. :silly: Gets an ACDelco alternator. Sent it.

Boomeranged two days later. Not charging. AND stored P0302 and P0306. I triple check everything with our new alternator. Still working. Another ACDelco and 60 miles of test driving. Customer is chomping at the bit to get their car back, so we send it again.

While it was back the second time, I grabbed another RC waveform. Sync on #6.

 

There's still something wrong with this engine. The PCM update was not a fix, just a Bandaid.