[BobLadd58]

When I cold start my 2017 Camaro SS it runs very rough and sounds like it’s misfiring. It seems to get worse when its colder. Once I drive the car for 1-2 minutes with some acceleration then it runs smooth. This only happens when it sits overnight almost never during the day when out an about. The engine light is on with code P0300. I’ve replaced the spark plugs and wires but still have the same issue.


I did make the mistake of running regular gas for a while (I was cheap) but went back to premium months ago after this problem occurred. My gas millage is pretty good, about 23 mpg and that’s mostly short runs.



My thought is that I may have a leaky or bad injector. What would be the best way to diagnose the actual cause of these rough starts?

Thanks Bob

[SSDan]

Is P0300 the only code you are getting? It would be nice if you could isolate it down to a cylinder or two. That way you could switch coil packs to eliminate that possibility. The same thing goes for injectors. Finding which cylinder(s) are misfiring is going to be the key to solving this I believe. I don't think running regular gas in the past is causing this.
Good luck and keep us posted. Getting a check engine light is frustrating.

[ctrlz]

Originally Posted by BobLadd58

My thought is that I may have a leaky or bad injector. What would be the best way to diagnose the actual cause of these rough starts?

Thanks Bob

Hook up a scan tool and check your fuel trims.
Since misfires are random, and not localized to one bank or cylinder, I would guess lean condition due to vacuum leak. Fuel trims would go rich to compensate.
Leaky injector I would think more likely to localize misfire to a bank or cylinder.

[BobLadd58]

I did have a misfire on cylinder 7 but I cleared it and it never returned. Kind of weird.