P0304 misfire code

[hobiebrat1]

Need some help.
I had the P0303 code and low compression in cyl 3 and 4. Rebuilt the top end and the misfire code went to P0304.
Checking compression all is good. 135, 125, 135, 125 cyl 1-4.
Replaced plugs, wires, rotor, cap, coil and still the same.
Read it could be the #4 injector heating up so we put an insulator in it - no change.
Replaced all the injectors. Ran better but same code.
Read it could be the O2 sensor. Replaced with aftermarket and got O2 errors. Replaced with NgT part and we are back to P0304 code.
Tested for vacuum leak by spaying brake clean to see if any increase in rpm. Nothing.

 

[hear]

Im confused why you say you have low compression but then say (and show) that the compression is ok across all 4 cylinders.

 

[macleanflood]

Mine was the crank position sensor...but it was random misfires on all cylinders... really time to verify injector wiring back to the PCM and verify the PCM connectors aren't corroded.

-Mac

 

[cpwolf]

Im confused why you say you have low compression but then say (and show) that the compression is ok across all 4 cylinders.

I think he stated that he "had" low compression, rebuilt top end, and now doesn't have low compression. I think, ha.

 

[hear]

I think he stated that he "had" low compression, rebuilt top end, and now doesn't have low compression. I think, ha.

oh i missed the rebuild bit.

 

[hobiebrat1]

Im confused why you say you have low compression but then say (and show) that the compression is ok across all 4 cylinders.

Yes, I had low compression on cyl 3 and 4, like below 100 psi, and had the P0303 code. I then rebuilt the head and the compression was fine and the code went to P0304.

 

[macleanflood]

Did the injectors go back in the same holes?

-Mac

 

[hobiebrat1]

Did the injectors go back in the same holes?

-Mac

I replaced them with new injectors so…

 

[cpwolf]

Need some help.
I had the P0303 code and low compression in cyl 3 and 4. Rebuilt the top end and the misfire code went to P0304.
Checking compression all is good. 135, 125, 135, 125 cyl 1-4.
Replaced plugs, wires, rotor, cap, coil and still the same.
Read it could be the #4 injector heating up so we put an insulator in it - no change.
Replaced all the injectors. Ran better but same code.
Read it could be the O2 sensor. Replaced with aftermarket and got O2 errors. Replaced with NgT part and we are back to P0304 code.
Tested for vacuum leak by spaying brake clean to see if any increase in rpm. Nothing.

I have read in the past that specific spark plugs, many different types, can throw this. I'm not an expert, but I'd look at some of the threads on that.

https://wranglertjforum.com/threads/p0304-cylinder-4-misfire.22261/