2011 GMC Acadia weirdness - ROUND 2... FIGHT

My very favorite Acadia is back! Link to the first thread:

www.scannerdanner.com/forum/post-your-re...nical-weirdness.html

Last time, it got a reman long block after we found the #6 rod bearing smoked. Last week it came back to me with a CEL, P0300 and P0306. Freeze frame shows the P0306 set within 45 seconds of a cold start. I can post the freeze frame capture if anyone wants it. My testing confirms this - the miss counts show up about 20-30 seconds into a cold start ONLY. Has to sit for 12 hours or more after getting fully warmed up. Runs well otherwise. Trims are always within 10%, VE is good. Both codes reset simultaneously. Here's a capture of the Misfire data list during the issue:

www.scanshare.io/share/1tcsa2yQn0GtVICem1Th2w

Relative compression and intake pulse shows a very slight dip on #6, but nothing crazy. Leak down on #6 is less than 5%. No bubbles in cooling system during leak down test. Compared to #4, identical. Borescope in #6 doesn't show anything abnormal. Pressurized cooling system and allowed vehicle to sit overnight, no coolant (or fuel) in cylinder the next morning. Head gasket test with the pressure pulse sensor and a manometer both pass.

Coils and plugs were moved from bank to bank, no change. Injectors are new and got installed with the replacement engine. Secondary ignition probes on #6 and another cylinder show a lean miss during a brake torque or snap throttle, so I warrantied the injectors with another set. No change.

What else am I missing here? :huh: I'll be setting this up to retest tomorrow morning, so gimme your best suggestions!

Good morning Tyler,

strange things happen....

Do you actually feel the miss? If so could you confirm that it is really #6?

Things I see in this data are; scan data does not indicate MIL on requset during the rise in misfire counter, airflow decreases when misfire begins, spark advances accordingly.

Does crank relearn affect in any way the beginning or length of the mifires?

Could you share the secondary captures (if you happen to have them while the mis happen as well, not only brake torque/snap throttle).

The new injectors didn't fix it? Bummer... I thought you were on the right track. B2 injectors have a higher commanded on time which supports your lean ignition pattern.
Probably not a schrader valve on the fuel rail?
Where it's the last cylinder on the head, maybe getting air/vapor (possibly water?) trapped in the rail? Could you easily purge the rail then run the fuel pump to charge the rail before the next cold start? Or if you can't purge the rail maybe just run the pump a few times before starting it?
Or run the injector balance test before starting it? Too bad it's such a small window of time for testing.
Idk, strange one indeed...

Noah, looks like GDI.... starts off with 10 MPa, no shrader valve there.

Great questions, Juergen. The misfire can be felt, but it doesn't feel severe. More of a weak contribution, less of a dead miss.

The MIL will come back on eventually. :silly: Takes two cold starts. Your boi here has been clearing codes. Oh yeah, speaking of, Mode $06 miss counts agree with the OEM data.

I thought about a crank relearn? Then I started to wonder if a relearn got done after the replacement engine was installed.   I'm going to do that today in preparation for starting it up cold tomorrow.

I can share the secondary captures, I just gotta take some screencaps on the Autel. LOVE the Autel scope, hate sharing captures.

No worries, Noah. :lol: There is a Schrader valve on the low side, right before the GDI pump. I forgot to mention that I took a fuel sample early on and didn't see anything abnormal. There's an injector balance option in the scan tool? But it lied to me before on GM GDI injectors in the past. That's why I relied on the secondary ignition more.

I could play with charging the rail prior to startup. Maybe the rail is draining out into the GDI pump, and it's working air out? But you'd figure it'd have more of a longer crank time...

Never mind, there is no crank relearn on this YMM. So much for a cheap fix. :silly:

Misfires appear to be happening right after the PCM shifts from base map to controlling fuel. Maybe add front O2s, fuel trims and loop status to the next startup capture. Might show evidence of the fuelling getting out of whack then correcting??

 

Regards the problem showing up on #6 does the new motor have enough miles on it for carbon build-up to be a suspect?

Does your Autel save waveforms in *.MSData format? I've got the MP408 software on my laptop but haven't been able to find any waveforms to play with.

A pulse sensor in the Exhaust Pipe and Intake Manifold during the cold start up might reveal something.  I would disable fuel and capture a good, long cranking waveform. Then, re-enable fuel and record from start-up, until after the miss stops.

I'll go for that tomorrow morning, Chad. I'll even use the Pico for ease of sharing.

I'm not brilliant at running intake/exhaust waveforms, so I'll definitely need some help!

If you can, capture the crank signal, too, when you do the running Intake and Exhaust waveforms.

wrote:

If you can, capture the crank signal, too, when you do the running Intake and Exhaust waveforms.

WHY IS NOTHING I DO EVER GOOD ENOUGH FOR YOU



























JK, I got the waveform. :lol: Email me and I'll send the files. They're too big for the forums, and I'm too buried in dumpster fires to parse them out right now. :silly:

For whatever it's worth, here's some Pico screenshots. Initial crank cold:

 

You can tell that one bank is pissed off, due to the uneven intake pulses every other cylinder. However, that goes away after an extended cranking time:

 

The exhaust pulse sensor didn't pick up much. Zoom in on the capture to get some detail if you want.

What's interesting is that when I started it this morning, the scan data showed #4 as misfiring worse than #6. :silly:

www.scanshare.io/share/6DKFHDgawkWAqbIL-o-rVQ

Following along with Chad's thought process, I captured the scope data during the same event and applied a frequency filter to the crank signal. The miss starts up after the high idle, and the scope capture kinda agrees.

 

Like I said, email me at wrenchturnsyou@gmail.com and I'll provide the raw captures. :) Next testing window is tomorrow morning.

The Crank Frequency definitely shows #4 as a low contributor. But, I think we can rule out valve sealing as the cause. Plugs, coils, and injectors...It seems you have covered your basics. May as well put a sensor on the dipstick tube, just for good measure. I'd like to see some more secondary captures, too. I've never tried scoping the fuel rail pressure sensor. I wonder if you can see individual pressure changes as the injectors fire.

I did put a pulse sensor in the dipstick tube early on, and didn't see much. I can do it again with the Pico. Maybe I'll get some ignition waveforms in there, too.

Honestly can't decide what my next move is. Really don't want to disassemble anything until I know what I'm looking for.

Does your Autel save waveforms in *.MSData format? I've got the MP408 software on my laptop but haven't been able to find any waveforms to play with.

It defaults to .DAT, but gives me an option for .TXT or .XLS. Dunno if that helps? :silly:

Did you smoke the intake when cold? Will the miss/code also appear after cranking the engine over several times with ignition and/or injection disabled and then staring it normally?

wrote:

I did put a pulse sensor in the dipstick tube early on, and didn't see much.
 

Be sure to blow through the hose/tube. If the dipstick tube extends into/below the oil level, it will muffle any pressure activity.

I have not smoked the intake? But the trims are always excellent. I can smoke it cold.

I had the same thoughts about the dipstick, Chad, so I did the same test with the sensor in the fresh air PCV tube. Same results. 

The last go-round, we did crank the engine for 20+ seconds before starting it. That's when the miss counts moved more to #4. It did not set codes that time. :huh: But every other time on a cold start, it has. Oil pressure? Lifter bleeding down? 

Finally got back around to playing with this one again. Got the Pico and a scanner rigged up for another cold start. Scope has an intake pulse sensor, crank signal, crankcase pulse sensor and #6 trigger. Crank signal once again confirms #4 and #6 as not contributing after about 30 seconds of running. The raw file is WAY too big for Kunena - email me. wrenchturnsyou@gmail.com :cheer:

I switched up to HPTuners because it was the only way I could find to watch ALL the PIDs I wanted at the same time. :silly: Put together a list of CMP angles, misfire counts, fuel trims and O2 signals, plus some other stuff because why not. Again, email me for the file. HPTuners VCM Scanner is free to download:

www.hptuners.com/vcm-scanner/

A screenshot for easy viewing:

 

I thought it was interesting that this go-round, the misfiring starts up NOT when it started idling down, but when the high pressure fuel pump started tapering off. :huh: Can't figure why that'd cause a miss on #4 and #6 and nothing else... It's also meeting desired rail pressure at all times. Cam timing is on. Fuel trims are a bit richer on bank two, but nothing crazy.

Again, I welcome any thoughts/ideas you might have.

wrote:

I thought it was interesting that this go-round, the misfiring starts up NOT when it started idling down, but when the high pressure fuel pump started tapering off. :huh: Can't figure why that'd cause a miss on #4 and #6 and nothing else... It's also meeting desired rail pressure at all times. Cam timing is on. Fuel trims are a bit richer on bank two, but nothing crazy.
 

Both the earlier scan logs showed the same thing for #6. A group of misfires right after what appears to be the PCM switching from base OL map to controlling fuel. Still at high idle. Appears to be taking fuel away when the misfires start. But doesn't start adding any back when they stop???

 

FWIW the graph top right of your HPTuners screenshot looks like the misfires happen after the engine idles down because the PID you're using is the total, history, misfires PID instead of the current misfires one. This screenshot shows current counter getting written to history and cleared.

 

I agree Matt, the fuel control strategy doesn't make sense. :huh: But, I've also never looked this closely at rail pressure during a cold start.

Yeah, I should have mentioned not to read too much into that chart. :silly: That was my first attempt at making a misfire chart in HPTuners. Just playing around to see what works/what doesn't.

Also FWIW, the number of misfires has gone down since it came in last week? It also didn't flag a P0300 or P0306 on the last startup. Dunno if there's anything to read into there...

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.