Feels like a misfire (coil packs?) - no fault codes detected

[wuffy68]

Here is Trifecta's very measured response to the issue ... these guys do sound like the real deal, but they really can't help until other things get resolved:

I gave them a slight correction to the behaviour:

I have to say - I've been saying 'mid-throttle ... or .... half throttle' - THAT is actually not the case. At half throttle, the performance is actually smooth and impressive - it's more at the 25 to 30% throttle where I keep feeling that Kangaroo hop.

 

[wuffy68]

I can't give you any specific data and I'm not a transmission guy, but Wuffy and I are having the same experience. I could describe, in detail, what it feels like to drive if you think it would help.

I'll also mention this because I suppose it could be related in some way. I have the following persistent trouble codes:

P0113 - Intake air temperature sensor - high input
P2227 - Barometric pressure sensor - range/performance problem
P2229 - Barometric pressure sensor - circuit high
P0097 - Intake air temperature sensor 2 - circuit low input; Intake air temperature sensor 2 circuit low voltage

In my case - there are no trouble codes ... just speculating based on YOUR codes - have you tried cleaning or replacing the MAF? Maybe start with checking that it's connected (while in the area, check to make sure the air filter is clean, and properly installed). The IAT (Intake Air Temp sensor is usually integrated into the Mass Air Flow (MAF) sensor on late model GMs)

 

[abizzle]

In my case - there are no trouble codes ... just speculating based on YOUR codes - have you tried cleaning or replacing the MAF? Maybe start with checking that it's connected (while in the area, check to make sure the air filter is clean, and properly installed). The IAT (Intake Air Temp sensor is usually integrated into the Mass Air Flow (MAF) sensor on late model GMs)

I read something about the MAF sensor having multiple other sensors built-in. If I unplug the sensor, the check engine light comes on. It will turn off soon after reconnecting, but the codes persist. I've tried to manually clear them as well. I'm gonna run another scan at lunch and see if they're still there.

I'll just set this to the side and treat it as a separate issue. I don't wanna cloud our discussion with info that doesn't apply to both of us. Sorry about that.

Here is Trifecta's very measured response to the issue ... these guys do sound like the real deal, but they really can't help until other things get resolved:

Yeah they're definitely the real deal. I continue to be impressed by the performance gains received from their tuning package. I can't remember... did you purchase the Trifecta Tune? Pretty sure we can say their tune has nothing to do with this issue. I would have expected the stutter to show up immediately following the ECM flash and that wasn't the case.

 

[wuffy68]

I read something about the MAF sensor having multiple other sensors built-in. If I unplug the sensor, the check engine light comes on. It will turn off soon after reconnecting, but the codes persist. I've tried to manually clear them as well. I'm gonna run another scan at lunch and see if they're still there.

I'll just set this to the side and treat it as a separate issue. I don't wanna cloud our discussion with info that doesn't apply to both of us. Sorry about that.


Yeah they're definitely the real deal. I continue to be impressed by the performance gains received from their tuning package. I can't remember... did you purchase the Trifecta Tune? Pretty sure we can say their tune has nothing to do with this issue. I would have expected the stutter to show up immediately following the ECM flash and that wasn't the case.

Nope - no tune on this one - wife's car, I don't drive it enough to justify the extra bump in power. I just contacted them to see if their tune could solve this occasionally reported issue by myself and other owners.

 

[wuffy68]

I've got one last silver bullet for this little gremlin ... way back, when I checked the air filter and the air filter box for disconnected hoses, connectors, 'n such, I cleaned the MAF with CRC MAF Cleaner - after which, the issue persisted, so I moved onto racing gas, plugs, CRC GDI cleaner, coils and VVT solenoids. I just ordered a new OEM MAF unit. I should have it tomorrow, hopefully this weekend I'll be able to tell if that was the problem all along. If so, I won't regret replacing the other components because I can tell, combined, they made the car run better at ~50K miles - they just didn't fix the part-throttle acceleration stumbling issue. What really chaps my hide is that two dealer techs couldn't 'feel' this issue while I was still under warranty. Another, at 20K miles, offered a $160 diagnostic to see if the valves needed walnut blasting (which apparently, wouldn't have been covered under warranty since they consider it a maintenance item). Note-to-self - always go on the test drive with your tech, since only you can reproduce your problem on-demand.

 

[wuffy68]

I've got one last silver bullet for this little gremlin ... way back, when I checked the air filter and the air filter box for disconnected hoses, connectors, 'n such, I cleaned the MAF with CRC MAF Cleaner - after which, the issue persisted, so I moved onto racing gas, plugs, CRC GDI cleaner, coils and VVT solenoids. I just ordered a new OEM MAF unit. I should have it tomorrow, hopefully this weekend I'll be able to tell if that was the problem all along. If so, I won't regret replacing the other components because I can tell, combined, they made the car run better at ~50K miles - they just didn't fix the part-throttle acceleration stumbling issue. What really chaps my hide is that two dealer techs couldn't 'feel' this issue while I was still under warranty. Another, at 20K miles, offered a $160 diagnostic to see if the valves needed walnut blasting (which apparently, wouldn't have been covered under warranty since they consider it a maintenance item). Note-to-self - always go on the test drive with your tech, since only you can reproduce your problem on-demand.

Put in the new OEM MAF (GM Genuine Parts ACDelco 23262344). Made in Japan - they've gone up in price recently. $71 was the cheapest OEM I could find online 🤔 I was optimistic at first, because the ECU had an adaptation period ... the CEL was on until I drove it for three short 'drive cycles'. The required adaptation period told me the new MAF was different enough for the ECU to recognise the swap. BUT in the end, no change in driving behaviour after driving it on a 40 mile round trip to the nearest town.

I did some further research on quirky torque converter lockup behaviour on these Aisin AWF8F45 8-speeds. I did a few light pulls using a "brake tap" method, where you keep your foot slightly on the brake during acceleration to prevent the torque converter from wanting to lock up. It seemed to stop having the shudder during these pulls (albeit it's not a very scientific method because it's hard to modulate the brake pedal while accelerating). A high volume transmission flush and filter replacement $$$ at the next oil service interval might do the trick. Fingers crossed.