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

[wuffy68]

My car when warm had a very, very slight "misfire" at idle. No codes, counts, etc. Just an occasional "that didn't feel right". I work with this stuff and am pretty overly sensitive to it. Didn't do it all the time, but every 2nd or 3rd day I'd notice it.

Anyway, delt with it for about 12,000 miles, then changed plugs at 39,696 mi. Plugs looked fine to me, but it's been cured about 3 weeks now.
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the left one in the second picture looks visibly cleaner than the others (like a lean condition on that cylinder?)

 

[adam728]

the left one in the second picture looks visibly cleaner than the others (like a lean condition on that cylinder?)

I think more of a camera / lighting /angle thing. All looked identical under magnification. And 0.032" gap. Certainly none look bad.

 

[abizzle]

Hey @wuffy68 I have something you can check. Check the cover on your air filter box and see if it’s on properly. There’s two tabs the cover slides into before you fold it down and tighten the screws. While replacing my air intake duct I noticed my cover was not installed correctly, creating a vacuum leak.

I put the cover on properly and the car accelerates without stuttering. If your air box cover is on properly, you might wanna start looking for a vacuum leak.

 

[wuffy68]

Hey @wuffy68 I have something you can check. Check the cover on your air filter box and see if it’s on properly. There’s two tabs the cover slides into before you fold it down and tighten the screws. While replacing my air intake duct I noticed my cover was not installed correctly, creating a vacuum leak.

I put the cover on properly and the car accelerates without stuttering. If your air box cover is on properly, you might wanna start looking for a vacuum leak.

Thanks - I'll check it out. It had the filter replaced at the dealer about six months ago, but the light shudder at mid-throttle hasn't gone away. I had another GM dealer do a diagnostic and test drove it - of course they didn't notice it. I looked and the car had the control arms replaced before we purchased it (probably part of the warranty recall). Still no codes or anything - runs great otherwise - haven't even breached 40,000 miles yet. Using Lucas Injector Cleaner (the one that says it BURNS WHITE HOT 😀) seems to improve things slightly, but it's still there. For whatever that's worth, ChatGPT says that "putting softer springs on a front-wheel-drive biased car could potentially cause it to feel like it's shuddering during mid-throttle acceleration [because under load, the softer springs can cause the front-end geometry to shift just enough to induce it]" . I'm wondering if this issue is isolated to the TourX models since they have softer/taller springs than the lower GS model.

 

[abizzle]

ChatGPT says that "putting softer springs on a front-wheel-drive biased car could potentially cause it to feel like it's shuddering during mid-throttle acceleration [because under load, the softer springs can cause the front-end geometry to shift just enough to induce it]

My issue was definitely a stutter and the lack of acceleration is noted by the tachometer and speedometer. I'm sure an OBD dongle with a decent app could generate a nice report. Then take that to the dealer and ask them if they can feel it now. 😀

 

[wuffy68]

My issue was definitely a stutter and the lack of acceleration is noted by the tachometer and speedometer. I'm sure an OBD dongle with a decent app could generate a nice report. Then take that to the dealer and ask them if they can feel it now. 😀

I checked the tabs like you suggested as well as the air filter and any vacuum connections under the engine cover. Haven't pulled the coils or the plugs yet. Everything looked OK - the tabs were inserted correctly. After driving it to Woodland Park, CO last night, I definitely noticed the shutter going up the twisty parts at mid-throttle using manual shift in 3rd gear. I'll have to pull the codes to see if there's anything "pending" from yesterday's drive. Otherwise it drove fine - we were getting consistent >36mpg doing 75mph+ coming back towards Denver on I-25 so it doesn't seem to impact efficiency. Having pulled the air cleaner cover off, it makes me think maybe the MAF sensor would be worth cleaning or replacing - but at 40k miles, there's really no oil residue in the turbo intake but IF it had been driven by the previous owner with those air cleaner tabs inserted wrong, there could be a chance some small leaf debris got caught inside the MAF to cause the issue.

 

[wuffy68]

Problem solved AFAICT ... stupidly it was overinflated tires. I'm used to running 40psi on my Chevy Volt to get the best range. I've been running 38-40 on the TourX for the same reason - since I rarely go over rough roads (I did yesterday while "Overlanding" up to a place called Wellington Lake, I sacrificed some ride quality for efficiency. This is why I didn't notice this behaviour when originally test driving the car, but noticed it a week later after pumping up the tires. I've never had a FWD biased car this sensitive to over-inflation (mostly it results in a harsher ride and less grip but not a shudder-like behaviour). I think with the fact the TourX is slightly lifted compared to the sedan models translates to extra "spring" during moderate acceleration when the tires are overinflated. I'm still running them over-inflated at 35psi instead of the factory recommended 32psi. The shudder is still there, but barely perceptible. I also think when the dealer mechanic test drove it - it was still pretty cold outside (December/January in Colorado), so the tire pressure never got above 33psi during their diagnostic test drive. I actually got the suggestion to reduce my tire pressure from ChatGPT 🤔
Anyway - I hope that helps others make their Regal the best it can be.

 

[adam728]

Problem solved AFAICT ... stupidly it was overinflated tires. I'm used to running 40psi on my Chevy Volt to get the best range. I've been running 38-40 on the TourX for the same reason - since I rarely go over rough roads (I did yesterday while "Overlanding" up to a place called Wellington Lake, I sacrificed some ride quality for efficiency. This is why I didn't notice this behaviour when originally test driving the car, but noticed it a week later after pumping up the tires. I've never had a FWD biased car this sensitive to over-inflation (mostly it results in a harsher ride and less grip but not a shudder-like behaviour). I think with the fact the TourX is slightly lifted compared to the sedan models translates to extra "spring" during moderate acceleration when the tires are overinflated. I'm still running them over-inflated at 35psi instead of the factory recommended 32psi. The shudder is still there, but barely perceptible. I also think when the dealer mechanic test drove it - it was still pretty cold outside (December/January in Colorado), so the tire pressure never got above 33psi during their diagnostic test drive. I actually got the suggestion to reduce my tire pressure from ChatGPT 🤔
Anyway - I hope that helps others make their Regal the best it can be.

I'll be quite surprised if the tire inflation has been your issue for 2 years. I'd either throw plugs in it, or get a decent scanner that lets you see misfire counts live.

As I posted before, I replaced stock plugs just before 40,000 miles from an idle misfire. I went with the 2 step colder plugs that are often recommended on LTG boards. By about 65,000 miles I had a mid throttle misfire, mostly when the engine was cold-ish (<5 or 6 min of driving). No codes, no stored codes, etc. Live monitoring showed what I was feeling was multiple misfires across all the cylinders pretty randomly, but never enough within the time window to throw a misfire code (I don't know the thresholds, but say 6 misfires from 1 cylinder in 5 seconds, or something). New stock plugs cured it. I'd say the colder plugs are maybe good if modded and driving the car fairly hard. Winter commuting in Michigan? They don't self clean well at those cylinder temps.

 

[Jack GS]

I don't want to assume the worst, but since I am actively sorting through a catastrophic piston failure that presented itself as a bad coil/misfire early on... it might not hurt to check compression. It's easy enough to do while you're swapping plugs/coils.

On our LTG, we were reading 145psi on cylinders 1-3 and cylinder 4 read 50psi. Leading up to the failure, we experienced almost identical symptoms. Jerky or grabby acceleration with acceleration over 3500rpm, but no other signs to point us towards the issue. We thought it was a bad coil or trans slip due to the infamous GM 8-speed (which has been an issue in the past).

It is very unlikely that this is your problem, but it costs nothing but a little time to check and rule out.

 

[abizzle]

I don't want to assume the worst, but since I am actively sorting through a catastrophic piston failure that presented itself as a bad coil/misfire early on... it might not hurt to check compression. It's easy enough to do while you're swapping plugs/coils.

On our LTG, we were reading 145psi on cylinders 1-3 and cylinder 4 read 50psi. Leading up to the failure, we experienced almost identical symptoms. Jerky or grabby acceleration with acceleration over 3500rpm, but no other signs to point us towards the issue. We thought it was a bad coil or trans slip due to the infamous GM 8-speed (which has been an issue in the past).

It is very unlikely that this is your problem, but it costs nothing but a little time to check and rule out.

I’m assuming my OBD app will report this info real-time? I’m gonna check it this evening.

 

[wuffy68]

I'll be quite surprised if the tire inflation has been your issue for 2 years. I'd either throw plugs in it, or get a decent scanner that lets you see misfire counts live.

As I posted before, I replaced stock plugs just before 40,000 miles from an idle misfire. I went with the 2 step colder plugs that are often recommended on LTG boards. By about 65,000 miles I had a mid throttle misfire, mostly when the engine was cold-ish (<5 or 6 min of driving). No codes, no stored codes, etc. Live monitoring showed what I was feeling was multiple misfires across all the cylinders pretty randomly, but never enough within the time window to throw a misfire code (I don't know the thresholds, but say 6 misfires from 1 cylinder in 5 seconds, or something). New stock plugs cured it. I'd say the colder plugs are maybe good if modded and driving the car fairly hard. Winter commuting in Michigan? They don't self clean well at those cylinder temps.

Thanks - you're probably right, I confirmed after driving the car in the mountains this evening, the problem hasn't gone away. Since my wife basically "idles" it back and forth to work on 55mph freeways and country two-lanes - she never complains about it. I put it in 3rd gear and at mid-throttle accelerated up my favorite section of the road (coming out of a sharp turn into a long straight with a moderate uphill climb). Definitely felt several jerks and can't blame the transmission hunting for a gear since it was in 3rd the whole way. I was at 7,000 ft in elevation, temperature was a cool 9°F, and had Shell V-Power 91 octane (that's the highest available here). Earlier in the fall, I tried 100 octane race gas from the local Mobile station, and it seemed to accelerate more smoothly - but I could still feel something wasn't right. Yea, plugs and coils are probably in order. What still gets me is that this has been a problem since the car only had 19,000 miles or so. It now has 42,000. Unusual for plugs and coils to start going out that early.

 

[wuffy68]

I don't want to assume the worst, but since I am actively sorting through a catastrophic piston failure that presented itself as a bad coil/misfire early on... it might not hurt to check compression. It's easy enough to do while you're swapping plugs/coils.

On our LTG, we were reading 145psi on cylinders 1-3 and cylinder 4 read 50psi. Leading up to the failure, we experienced almost identical symptoms. Jerky or grabby acceleration with acceleration over 3500rpm, but no other signs to point us towards the issue. We thought it was a bad coil or trans slip due to the infamous GM 8-speed (which has been an issue in the past).

It is very unlikely that this is your problem, but it costs nothing but a little time to check and rule out.

Will definitely check while I have them removed - Thanks. And yes, the problem is still there. Full details in my reply to adam728 above.

 

[Mordor67]

My 2019 does the same thing. 37 k now but has done it since 18 k when I bought it

 

[thrasherht]

I think this is a modern GM turbo problem. Both my tourx does it, and my old 2012 Cruze with the 1.4 turbo did it. Those both only did it while the car was still heating up. Once it was too temp and in open loop, they stop doing it. It is only slight for me, nothing major.

My cruze improved when I swapped to the ZZP coil pack and tighter plugs.

 

[RETLAW]

Could be an issue with the VVT solenoids. I have some kinda surging issues and not pulling very well past 4500rpm. Changing mine Tuesday, seems straight forward and inexpensive.

 

[Rich B.]

This topic goes back a bunch of years too (looked this time). Just hi-lighting on info but higher octane gas maybe not a fix with this? Would more relate to knocking/pinging and timing setback. I would say too much water/condensation in fuel might be place to start. Believe fuel injection would have enough pressure behind it to just push droplets of water right through though?

Dry Gas doesn’t do away with water, only say dissolves it so will flow and plugs will fire as advertised. And it’s Winter again, cold nights-days balmy, half full tank… oh well, can even occur with oil. Pull dipstick and if kinda milky looking same difference. Or you just had oil and antifreeze lines connected together by mechanic installing engine heater. Saw only once and was laughing so hard got stomach cramps. Mechanic said something like “Gee, we need to change the oil now”.

PIC- is water actually plugging and pushing through injectors, actual frozen water in fuel lines or even fuel pump strainer. Not same thing as water/methanol injection. Can use windshield washer with that, water mixed with rubbing alcohol.

 

[Mordor67]

Could be an issue with the VVT solenoids. I have some kinda surging issues and not pulling very well past 4500rpm. Changing mine Tuesday, seems straight forward and inexpensive.

Let us know if it helps

 

[RETLAW]

Changed VVT solenoids and it seems to have smoothed out my engine under load and now revs much more freely past 4k rpm. Just something to think about if your still having issues. Good luck.

 

[wuffy68]

Long time since the last update in the drawn-out analysis ... the car now has 48k miles and I swapped the plugs (used NGK 94374 LTR6IX Iridium IX), along with running CRC GDI Turbo/Intake Valve cleaner through it. I couldn't find my dad's (RIP) compression gauge (I think it got thrown out when we were cleaning the garage 😢 At first, it seemed like the plugs and cleaner might have helped ... I took it on a 3 hour road trip afterwards - it seemed to run "better" on the highway (I took it up to well past the double-nickel ... several times - although it still felt like something was 'missing' (pun intended). Once I got back to my neighborhood streets, starting from a stoplight, I noticed the same behaviour. It just isn't a joy to drive at mid-throttle acceleration like similar vehicles I've driven. My next step is to swap the ignition coils. Using the GM module for the Torque App - I did see misses all around, but mostly on #2 and #3 cylinders (pre-plug replacement). Attaching images of the OEM plugs I pulled. I don't see anything too unusual between the four plugs - except the carbon deposits around the base. I'm used to seeing more of a clean-burned/brown crust on my older port-injected VW/Audi products....

 

[wuffy68]

This topic goes back a bunch of years too (looked this time). Just hi-lighting on info but higher octane gas maybe not a fix with this? Would more relate to knocking/pinging and timing setback. I would say too much water/condensation in fuel might be place to start. Believe fuel injection would have enough pressure behind it to just push droplets of water right through though?

Dry Gas doesn’t do away with water, only say dissolves it so will flow and plugs will fire as advertised. And it’s Winter again, cold nights-days balmy, half full tank… oh well, can even occur with oil. Pull dipstick and if kinda milky looking same difference. Or you just had oil and antifreeze lines connected together by mechanic installing engine heater. Saw only once and was laughing so hard got stomach cramps. Mechanic said something like “Gee, we need to change the oil now”.

PIC- is water actually plugging and pushing through injectors, actual frozen water in fuel lines or even fuel pump strainer. Not same thing as water/methanol injection. Can use windshield washer with that, water mixed with rubbing alcohol.

In my vehicle's case - the symptoms are evident in snowy mid-January in -13°C all the way to sunny, dry mid-July at 39°C ... nearly identical behavior.