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

[wuffy68]

Howdy - I'm new to the forum. Recently purchase a 2018 TourX with only 18,500 miles - Lease Return. Didn't notice the problem during the test drive, but within a week, noticed a slightly jerky acceleration at mid-throttle. It really became apparent driving the car after a rainstorm with a lot of humidity in the air. It's a familiar feeling I've experienced in a Volvo S40 (1.9T) which I've worked on in the past, and our older Audi A6 2.7T when the coil packs started going out at 120,000 miles. I've run both 91 octane (only one available locally) and 87 mid-grade. Octane doesn't seem to effect the behaviour - idle is smooth either way and feels strong (for a 2.0) on the highway. Is it common for coil packs with only 18,000 miles to start going out? Does GM use a cheaper grade of coil pack susceptible to early failure (don't laugh at this obvious question 😛)? I scanned for fault codes or pending faults - there are none. The car has an extended warranty, so I'm assuming a trip to the dealer is in the near future - however just want to make sure this isn't just normal behaviour on the 2.0 LTG.
Love the car so far, for what it is (hardly any others on the road) - averaging nearly 30mpg in a vehicle this quick, and this large is pretty amazing.

 

[FavaBean]

There hasn't been much talk about coil packs here. So I wouldn't say that GM intentionally used an inferior product.

However, I did have to replace one coil pack at 55k. The check engine light flashed and threw a code indicating which cylinder was at fault. It rendered the vehicle almost useless.

I now carry an extra coil pack in the vehicle at all times, because frankly.. that was some scary sh!t. I was only a mile from my house but the car nearly couldn't make it up the slightest of incline.

I will say that I have gotten surging acceleration if the engine temp is below operating temperature. But that is independent of outside humidity levels.

 

[abizzle]

Finally! Someone is reporting my same issue. It’s been going on for about 8 months and I’m not getting any error codes either. I decided to try some routine maintenance before I take it to the dealer, but I haven’t made time. I bought a new set of OEM plugs, even though I’m only at 52K miles, and I bought two 12oz bottles of Techron.

I figured if the problem is still there after two fuel treatments and new plugs, it’s time for the dealer to take a look. The problem seems to have gotten progressively worse and it’s more pronounced when running in Performance mode.

I was kinda hoping someone had successfully diagnosed a bad coil pack because I’d like to upgrade the OEM packs.

I will change the plugs tonight and let’s see if they’re fouled.

 

[abizzle]

I’m gonna have to wait until morning to change plugs. I just got home and I don’t feel like waiting up for the engine to cool. Will report back after installation.

 

[abizzle]

@wuffy68 did you happen to do any troubleshooting on the throttle? I changed plugs and I’m on my second tank of Techron, and it hasn’t made any difference. My brother suggested cleaning the throttle body and mass airflow sensor, so I guess I’ll do that.

I’m gonna have to take it to the dealer next week, as I only have 500 miles left on my warranty.

 

[wuffy68]

@wuffy68 did you happen to do any troubleshooting on the throttle? I changed plugs and I’m on my second tank of Techron, and it hasn’t made any difference. My brother suggested cleaning the throttle body and mass airflow sensor, so I guess I’ll do that.

I’m gonna have to take it to the dealer next week, as I only have 500 miles left on my warranty.

I haven't yet - sorry. It's my wife's daily driver, and she doesn't really care as long as it goes from A to B. My other thought was that it could be the 8 speed hunting for the right gear. I haven't tried to just put it in 2nd or 3rd using the Auto-Man to see if the jerk shows up when the TCM doesn't have to do any thinking. But haven't had the opportunity since I wrote the question.

 

[abizzle]

I haven't yet - sorry. It's my wife's daily driver, and she doesn't really care as long as it goes from A to B. My other thought was that it could be the 8 speed hunting for the right gear. I haven't tried to just put it in 2nd or 3rd using the Auto-Man to see if the jerk shows up when the TCM doesn't have to do any thinking. But haven't had the opportunity since I wrote the question.

I’ve been meaning to make some notes, like what are the RPM when you start feeling it and whether or not it can be replicated with manual shifting. I wanna say it starts around 3500 RPM and I can feel it both with and without turbo boost.

 

[saab93driver]

I’ve been meaning to make some notes, like what are the RPM when you start feeling it and whether or not it can be replicated with manual shifting. I wanna say it starts around 3500 RPM and I can feel it both with and without turbo boost.

Shot in the dark but have you tried disconnecting the battery for a while to erase any “learning” the ecu may have stored?

 

[Rueme]

I had an uneven idle at 25K, like a surge at idle, so I put new AC Delco iridum plugs in and now its fine, two of the old plugs looked kind of burnt to me

 

[abizzle]

Shot in the dark but have you tried disconnecting the battery for a while to erase any “learning” the ecu may have stored?

Not specifically for this problem, but I’ve had the battery disconnected a few times for other things.

 

[wuffy68]

I’ve been meaning to make some notes, like what are the RPM when you start feeling it and whether or not it can be replicated with manual shifting. I wanna say it starts around 3500 RPM and I can feel it both with and without turbo boost.

Today, I did try it a little bit with manual shifting but I couldn't go too crazy (I had four passengers and junk in the back). It did seem better with manual shifting than in full auto, but I still could tell it wasn't quite right. I was running 91 octane today, but I didn't make note of RPMs. It does seem to show up most at about 30% throttle position under moderately "spirited" acceleration. At full throttle, its much harder to tell since with 8 gears, the revs don't drop much.

 

[abizzle]

Today, I did try it a little bit with manual shifting but I couldn't go too crazy (I had four passengers and junk in the back). It did seem better with manual shifting than in full auto, but I still could tell it wasn't quite right. I was running 91 octane today, but I didn't make note of RPMs. It does seem to show up most at about 30% throttle position under moderately "spirited" acceleration. At full throttle, its much harder to tell since with 8 gears, the revs don't drop much.

I even considered the fuel as a possible cause, so for the two tanks of fuel I ran with Techron I got it from a different station than normal. I’ve only used 93 octane since I got the car.

 

[wuffy68]

I even considered the fuel as a possible cause, so for the two tanks of fuel I ran with Techron I got it from a different station than normal. I’ve only used 93 octane since I got the car.

91 is the highest octane available in my area (Colorado) unless you go to race gas. The behaviour seems octane independent - actually it seems less noticeable with our mid-grade (87 octane). With only 19K miles I don't think it needs techron yet? But looking forward to what the dealer tells you.

 

[abizzle]

Just keeping in touch. I feel kinda feel bad because I said I was gonna take the car to the dealer and i haven’t. I found out that I had another 1200 miles on my warranty and it expires in Nov 2023.

I just haven’t been too excited about going to the dealer because I’m anticipating them keeping it all day and then asking me to leave it overnight. They have never been able to supply a loaner.

 

[wuffy68]

Some light bathroom reading ... these guys go into some depth on an older (2014) LTG with a similar problem. One thing that is suggested ... one defective injector could be causing the knock sensor to retard timing without throwing any fault codes (almost like running low octane gas). A faulty spray pattern on one injector at part-throttle could "even out" at larger or WOT positions. I'm going to try monitoring the "Knock Retard" setting through my Torque Lite app although I might have to upgrade to the Pro version to get GM specific sensor monitoring:

https://www.reddit.com/r/Cartalk/comments/dxtza8

 

[abizzle]

Some light bathroom reading ... these guys go into some depth on an older (2014) LTG with a similar problem. One thing that is suggested ... one defective injector could be causing the knock sensor to retard timing without throwing any fault codes (almost like running low octane gas). A faulty spray pattern on one injector at part-throttle could "even out" at larger or WOT positions. I'm going to try monitoring the "Knock Retard" setting through my Torque Lite app although I might have to upgrade to the Pro version to get GM specific sensor monitoring:

https://www.reddit.com/r/Cartalk/comments/dxtza8

Thanks for digging that up! That reminds me… I have been meaning to hook up the flash cable I got from Trifecta and see which parameters I can monitor in real time.

 

[abizzle]

Hey @wuffy68 I took my car to the dealership on Monday and had them look into the throttle stuttering issue. They told me they couldn’t replicate the problem and it wasn’t giving a code, so there’s no problem.

They told me I can have a technician ride with me, so I can demonstrate the problem to him. I guess it’s back to the dealership next week.

 

[LARRY70GS]

OBD2 has a misfire log. Any decent scan tool can access that log. No need to guess if it is a misfire or not. The PCM knows how many times it misfired, and which cylinders.

 

[wuffy68]

OBD2 has a misfire log. Any decent scan tool can access that log. No need to guess if it is a misfire or not. The PCM knows how many times it misfired, and which cylinders.

Hey @wuffy68 I took my car to the dealership on Monday and had them look into the throttle stuttering issue. They told me they couldn’t replicate the problem and it wasn’t giving a code, so there’s no problem.

They told me I can have a technician ride with me, so I can demonstrate the problem to him. I guess it’s back to the dealership next week.

Agree with @LARRY70GS ... technicians are often numb to issues like this (especially if it's warranty work 😀 - and if it's not? "Allow me to direct you to the showroom where you can purchase a new car without this issue") ... I have to update my Torque Lite to Torque Pro so I can see if there's any pinging going on with mine. I haven't had time to deal with it - and the way my wife drives the car - she doesn't really care - but its still the same AFAICT. It's scheduled for it's first oil change (since I've had it) and some recall work next month otherwise. I can bring it up then.

 

[adam728]

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.