TROUBLE CODE P0304

  • Tiny
  • bschrum
  • 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?

Monday, November 28th, 2011 AT 7:41 PM

8 Answers

  • Tiny
  • Wrenchtech
  • Expert
  • 19,541 posts

Did you try swapping the plug with another cylinder too?

Take a compression test also.

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Monday, November 28th, 2011 AT 8:10 PM
  • Tiny
  • ASEMaster6371
  • Expert
  • 25,502 posts

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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Monday, November 28th, 2011 AT 8:12 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,541 posts

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.

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Monday, November 28th, 2011 AT 9:04 PM
  • Tiny
  • bschrum
  • Member

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).

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Tuesday, November 29th, 2011 AT 3:55 AM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,541 posts

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.

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Tuesday, November 29th, 2011 AT 10:48 AM
  • Tiny
  • bschrum
  • Member

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.

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Tuesday, November 29th, 2011 AT 2:44 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,541 posts

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.

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Tuesday, November 29th, 2011 AT 8:03 PM
  • Tiny
  • bschrum
  • Member

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?

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Tuesday, November 29th, 2011 AT 10:24 PM

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