Mechanics

TROUBLE CODE P0304

2005 Chevrolet Colorado • 92,000 miles

Two weeks ago the vehicle developed a misfire. Scanner gave a P0304 code stating cyl. No. 4 misfire. Replaced the coil which cleared the problem for two weeks. Same problem - same code. Part store exchanged the coil. Installed new coil but misfire still there. Swapped coils on cylinders - problem stayed on cyl. 4. Checked wiring and found nothing. Have +12v on pink wire - ground on black - looks like pulses on green wire (at least #4 looks like the other cylinders). Pulled PCM off firewall to inspect it - found nothing obvious. After putting PCM back cyl. 4 still misfiring, door locks do not work, driver's window will not move, and clock reset to 1200. Do I have a bad plug at the PCM or do you think there might be other issues?
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Bschrum
November 28, 2011.




Did you try swapping the plug with another cylinder too?

Take a compression test also.

Wrenchtech
Nov 28, 2011.
First of all, you missed the obvious. Try changing the spark plug and I bet your issue with the 304 is gone

if you disconnected the pcm, you now have to have the pcm re flashed or re programmed. You ereased the memory in the pcm.

Roy
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ASEMaster6371
Nov 28, 2011.
You shouldn't have any programming problems with the PCM. It will lose the adaptive memory and any codes stored but that should be all.

Wrenchtech
Nov 28, 2011.
Changed the spark plugs with the new coil with no improvement. Compression is good. Did not disconnect the PCM - just detached it from the firewall (plastic fingers).

Tiny
Bschrum
Nov 29, 2011.
If the spark is good, compression is good, that only leaves the fuel injector. You can try moving that injector to a different cylinder to see if the misfire moves with it.

Wrenchtech
Nov 29, 2011.
Thought about the injector too. I was probably not clear. I changed the spark plugs but still have no spark out of four. I put a plug in the coil out of the cylinder to check that. Checked all the voltages on the plug but not sure if I am seeing pulses on the green wire. That is the wire that goes back to the PCM. With all the other issues (door locks, driver's window, and radio) I am still wondering about the plug going into the PCM.

Tiny
Bschrum
Nov 29, 2011.
If you have power and pulse to the coil, you should have spark if the coil is good, assuming you are grounding the spark plug or using a spark tester which is what you should be doing.

Wrenchtech
Nov 29, 2011.
I know I have power and ground but I am not sure if I have pulse to coil. Any down and dirty way to test that?

Tiny
Bschrum
Nov 29, 2011.

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