He just said compression is normal.

I don't know what a #2 fuel sensor is.

You might try fuel injector Cleaner, or even replacing the injector, as was suggested earlier.

 

Sorry i meant fuel injector, i updated it. I only replaced #2.

Compression test was done by the mechanic, so i dont have the numbers but they said it was normal.

 

Is coolant disappearing? Oil level increasing? Water in oil? =blown head gasket.
Wires to cylinder #2? #1 is the end with the serpentine belt, just to be sure.
The reason P0302 comes and goes is that it has to happen a few times before the light goes on. Don't worry about stored/historic/permanent codes, only current and pending matter. Pending means it has happened but not enough to set a code. Current means it has happened enough to set the code.

 

Just out of curiosity, what year/make/model was the replacement motor from?

 

A Cobalt, no year mentioned

 

I don’t remember, I’m trying to locate the receipt.

but yes it was a cobolt.

 

Year and displacement are important, they will fit but the 2011 was a little different, shouldn’t matter for the code you’re dealing with.

 

The only Cobalt motor that would make sense would be the LAP from 2009-2010. No other 2.2L was used on Cobalts. But that was not a flex-fuel motor. The differences could explain misfires, if not misfires on a single cylinder.

I have no idea what the exact differences are other than it absolutely must have completely different ECM program.

It would probably have different injectors, because running E85 requires more fuel. If so, you would need to bring the old injectors along if you’re running the HHR ECM, which thinks it’s running an LE8, not an LAP.

I’m not sure I’m clear on when you changed the #2 injector relative to when other stuff was done and when the trouble started. You may have gone from a bad injector in #2 to a mismatched injector in #2. That would mean #2 getting a completely different a/f both before and after, right?

I’d also look into whether the cams and phasers are the same. If not you should swap those too. VVT tends to be much more aggressive on FlexFuel. There might be other differences. MAF? MAP sensor? Throttle body?

 

That’s probably the case, the 2011 HHR has a different part number for the injectors then the 2010 Cobalt

 

It was a 2010 cobolt.

8th Digit on the HHR is W.

These will all fit

COBALT 10 2.2L (VIN 5, 8th digit, opt LAP), Federal emissions (opt NT7)
COBALT 09 2.2L (VIN H, 8th digit, opt LAP), Federal emissions (opt NT7)
G5 09-10 (2.2L, VIN H, 8th digit, opt LAP), Federal emissions (opt NT7)
COBALT 10 2.2L (VIN 5, 8th digit, opt LAP), California emissions, opt NU1
HHR 09-10 2.2L (VIN B, 8th digit, opt LE8)
HHR 11 2.2L (VIN W, 8th digit, opt LE8)
COBALT 09 2.2L (VIN H, 8th digit, opt LAP), California emissions, opt NU1
G5 09-10 (2.2L, VIN H, 8th digit, opt LAP), California emissions, opt NU1