[EMTNLSS]

So i'm having this issue where I seem to be getting a misfire mainly in cylinder #7 and maybe #8 only during the cold start sequence. I'll log it with hp tuners and it'll misfire for most of the cold start sequence then once it calms down it'll show no misfires. I went out and drove it around going to redline and everything and got pretty much no misfires. Maybe like 1 or 2 but I feel like that's normal.

I've checked the wire and it seems fine. I replaced the spark plug with the OEM ACDelco one and it's still misfiring. I'm thinking about switching the coil to another cylinder and see if the misfire switches. Any ideas on why it would only misfire during a cold start? Mods are in my sig. Thanks!

[GZL1]

Mine does it too. Goes away when it warms up. I'm not sure why it does it either.

[JamesNoBrakes]

Yes, and it got pretty bad, regardless of outside temp (because it was coming from inside a warm garage).

Unfortunately, it's turned into quite the ordeal, I was out for surgery for a bit, but it's been since November and the dealer hasn't figured it out. Originally, they tried to blame it on the catch-can (wtf?), then it was "bad gas". We removed the catch can well before Xmas and that was ruled out. Now it's who knows, they did the flush and have new gas in it, but won't tell me what is still wrong. I've been in contact with GM customer assistance and had a ticket open from last year about this. At one point, they told me, "oh yeah, it's all good, we just have to start it up when it's cold and make sure it's good". They were supposed to do that on a Monday, but never did, never called me, I called them on a Wednesday and it was "oh, um, let me go start it up and I'll get back to you", and then it was "um, yeah it's still doing it, we need to get it back in and take a look at it". Then of course, it was the "bad gas". If there truly is bad gas, I'm going to claim it against Costco, the only place I've filled it, but I'm not sure if I'm going to accept that if the car still has the issue, that's a faulty diagnosis and if they try to push the issue I may take them to court. Last week I was pretty harsh with them, because they said they'd get back to me with more information and then couldn't tell me what was going on, what was my car still doing exactly? The dealer wasn't much more helpful, eventually I was able to get from them (on Friday) that some machine was needed to "calibrate" my car, but the machine was "out of calibration". As you can see, they aren't being specific and it sounds like they are being intentionally deceitful, as I have a hard time believing their service personnel are so incompetent that they don't know the correct terms for what the problem may still be. Even the senior service tech from customer assistance made some comments to the fact that he couldn't get any information from the dealer and that he "didn't think they were bluffing". That's a damn-odd comment to make. I have been documenting this all along and I'm about to write a lemon-law case, which I may or may not need based on what I learn tomorrow, but needless to say I'm not happy. I have a suspicion it's either the coils or the injectors as has been commonly reported for this issue, which I made them aware of the first time I brought it in.

As you say, it goes away after it warms up.

[vtirocz]

Originally Posted by JamesNoBrakes

Yes, and it got pretty bad, regardless of outside temp (because it was coming from inside a warm garage).

Unfortunately, it's turned into quite the ordeal, I was out for surgery for a bit, but it's been since November and the dealer hasn't figured it out. Originally, they tried to blame it on the catch-can (wtf?), then it was "bad gas". We removed the catch can well before Xmas and that was ruled out. Now it's who knows, they did the flush and have new gas in it, but won't tell me what is still wrong. I've been in contact with GM customer assistance and had a ticket open from last year about this. At one point, they told me, "oh yeah, it's all good, we just have to start it up when it's cold and make sure it's good". They were supposed to do that on a Monday, but never did, never called me, I called them on a Wednesday and it was "oh, um, let me go start it up and I'll get back to you", and then it was "um, yeah it's still doing it, we need to get it back in and take a look at it". Then of course, it was the "bad gas". If there truly is bad gas, I'm going to claim it against Costco, the only place I've filled it, but I'm not sure if I'm going to accept that if the car still has the issue, that's a faulty diagnosis and if they try to push the issue I may take them to court. Last week I was pretty harsh with them, because they said they'd get back to me with more information and then couldn't tell me what was going on, what was my car still doing exactly? The dealer wasn't much more helpful, eventually I was able to get from them (on Friday) that some machine was needed to "calibrate" my car, but the machine was "out of calibration". As you can see, they aren't being specific and it sounds like they are being intentionally deceitful, as I have a hard time believing their service personnel are so incompetent that they don't know the correct terms for what the problem may still be. Even the senior service tech from customer assistance made some comments to the fact that he couldn't get any information from the dealer and that he "didn't think they were bluffing". That's a damn-odd comment to make. I have been documenting this all along and I'm about to write a lemon-law case, which I may or may not need based on what I learn tomorrow, but needless to say I'm not happy. I have a suspicion it's either the coils or the injectors as has been commonly reported for this issue, which I made them aware of the first time I brought it in.

As you say, it goes away after it warms up.

Do you have any fault codes?

[KLR ZL1]

Humm this is interesting. I have noticed on cold starts that as the idle starts to drop to 1000 rpm the motor has a rough idle then stops. Not sure if this is the same thing , but it sure sounds like it. I believe it to be the DI injectors. I have blipped the throttle when it does it and it stops. I have also held the throttle at about 1200 rpm and it seems to not be as rough. I hate bringing my vehicles to the dealers because they are incompetent and or damage my vehicles. And that has happened more than I care to say and is a whole new issue to deal with. So I hope it isn't too serious and someone can chime in to give us a remedy.

[JamesNoBrakes]

Originally Posted by vtirocz

Do you have any fault codes?

None.

[JamesNoBrakes]

Originally Posted by KLR ZL1

Humm this is interesting. I have noticed on cold starts that as the idle starts to drop to 1000 rpm the motor has a rough idle then stops. Not sure if this is the same thing , but it sure sounds like it. I believe it to be the DI injectors. I have blipped the throttle when it does it and it stops. I have also held the throttle at about 1200 rpm and it seems to not be as rough. I hate bringing my vehicles to the dealers because they are incompetent and or damage my vehicles. And that has happened more than I care to say and is a whole new issue to deal with. So I hope it isn't too serious and someone can chime in to give us a remedy.

At high RPM it seems to not happen, even when cold, but at low RPM, like you'd normally be driving at initially, it's most prevalent, until it's warmed up. I'm not sure if that meant that at high RPM it was still happening and I just couldn't detect it, but at low RPM the effect was easy to detect, car jerking as it was misfiring.

[Umbriel]

Faulty injectors?

[sadpanda]

injectors, fuel rails, coil packs, plugs... data log is your best friend. Costco fuel though?

[SSDan]

Originally Posted by sadpanda

injectors, fuel rails, coil packs, plugs... data log is your best friend. Costco fuel though?

You can get a bad tank of gas just about anywhere regardless of brand. However, Costco gas is rated top tier and they sell a lot of volume. So, the chances are you'll get good gas there are better than most anywhere.

[sadpanda]

I had no idea costco was a top tier vendor.... Learn something new every day.

[RyanR623]

Originally Posted by JamesNoBrakes

Yes, and it got pretty bad, regardless of outside temp (because it was coming from inside a warm garage).

Unfortunately, it's turned into quite the ordeal, I was out for surgery for a bit, but it's been since November and the dealer hasn't figured it out. Originally, they tried to blame it on the catch-can (wtf?), then it was "bad gas". We removed the catch can well before Xmas and that was ruled out. Now it's who knows, they did the flush and have new gas in it, but won't tell me what is still wrong. I've been in contact with GM customer assistance and had a ticket open from last year about this. At one point, they told me, "oh yeah, it's all good, we just have to start it up when it's cold and make sure it's good". They were supposed to do that on a Monday, but never did, never called me, I called them on a Wednesday and it was "oh, um, let me go start it up and I'll get back to you", and then it was "um, yeah it's still doing it, we need to get it back in and take a look at it". Then of course, it was the "bad gas". If there truly is bad gas, I'm going to claim it against Costco, the only place I've filled it, but I'm not sure if I'm going to accept that if the car still has the issue, that's a faulty diagnosis and if they try to push the issue I may take them to court. Last week I was pretty harsh with them, because they said they'd get back to me with more information and then couldn't tell me what was going on, what was my car still doing exactly? The dealer wasn't much more helpful, eventually I was able to get from them (on Friday) that some machine was needed to "calibrate" my car, but the machine was "out of calibration". As you can see, they aren't being specific and it sounds like they are being intentionally deceitful, as I have a hard time believing their service personnel are so incompetent that they don't know the correct terms for what the problem may still be. Even the senior service tech from customer assistance made some comments to the fact that he couldn't get any information from the dealer and that he "didn't think they were bluffing". That's a damn-odd comment to make. I have been documenting this all along and I'm about to write a lemon-law case, which I may or may not need based on what I learn tomorrow, but needless to say I'm not happy. I have a suspicion it's either the coils or the injectors as has been commonly reported for this issue, which I made them aware of the first time I brought it in.

As you say, it goes away after it warms up.

Man that's awful, sorry to hear man. Is there another GM dealer by you can take it to? Sounds like you found the worst one ever!

[vtirocz]

I noticed mine has a little bit of misfire on cold starts, on just a very specific light pedal maneuver shortly after a cold start. It's a small window where this can occur and once the engine is warm everything is fine. No faults in my case either. I test drove an automatic transmission '16 Camaro SS (this was a couple years ago, so my memory is a bit fuzzy), but I recall that one being similar. I suspect GM was aggressive with their tune to warm up the catalysts quickly to meet the emission standards. Do a search on here and there's several other threads regarding light stumble/misfire during warmup and light pedal / low engine speed maneuvers only. In the dealer's defense, if the stock tune is just on the hairy edge during warm-up to meet emissions, there's not a whole lot they can do other than throw parts at it.

[HCGxKaLiBeR]

My car was doing the same thing. One day I thought I hear hissing noise during cold start. Then I Unpluged and repluged all the vacuum hoses I could find in the engine bay fixed the issue. Some how that fixed my transmission rough shift issue as well...