I have a P0301 code. So far I have tried:
- Tune up
- Swapped #1 coil with #4 coil
- Swapped #1 fuel injector with #2 fuel injector
- fuel filter change out (past time to do this anyway)

Now, I still have this code!! Only thing I can think of now is to check the wiring harnesses (fuel & ignition) to find any possible shorts or bad grounds... Does that sound right to you guys? And does anyone have a schematic I could download?

 

Might not hurt to check compression/leakdown on #1 if its actually missing. Ive seen alot of valve issues.

 

Bump for some help please... Gonna try the compression / leakdown test(thank you THEMISSLE)... Anything else? Would really like an Ignition Harness schematic and/or fuel system harness schematic. Can anyone help ?

 

do the test first at this point.. dont toss anymore useless money at it if its POSSIBLY got a serious problem.. like rings, or valve problem

you already covered the basics.. provided you know which cylinder is cylinder #1... but then again you swapped 1 with 4, so thats fool proof

 

any results on the compression and leak down test yet?

 

I saw you swapped coils but what about plugs? I'm having the same problem with my LNF although I haven't done the injector yet.

 

Haven't been able to do leak down test yet. Planning to do it on Sunday.
Yes, I installed new NGK plugs. Made sure to check gap before putting them in also.
I have over 88,000 miles on it, so kinda worried about the leakdown test showing the problem.

 

Update... Did leakdown test and everything was good. This is really throwing me for a loop!! Any other suggestions?

 

What about compression test?

 

Ive had a motor leakdown just fine, but the compression check was way low. And vice versa. So make sure you check compression too. If thats not the issue then you may have a different cylinder causing your issue.

Misfire counters arent always 100% accurate as they use your CKP variance to determine which cylinder has the misfire. So sometimes #4 is throwing a misfire code but #6 is actually misfiring. Its not very common in 4 cylinders since there is only 4 cylinders to track, whereas a v8 is tracking double the amount.

 

Any update with your Cobalt? I'm having the same problem. Misfires randomly usually around 172degrees. And misfire in the top at high boost.. I'm gonna swap out my thermostat so my at will hopefully warm up properly.
I have all stock parts with tune. I think I have a boost leak or my stock by pass vavle is giving out. Not sure.

 

I have a 2007 Cobalt SS and have a p0301 code. So far I've changed coils,plugs,coil pack harness,injectors, injector harness, done compression test that all came back between 195 and 200. Only noticeable when idling and decelerating, no type of indication of misfire when accelerating. Car has ZZP stage 3 upgrade kit with 2.8 pulley, dual pass, option b, and front mount heat exchanger. Any help would be greatly appreciated.