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Trouble code P0304

Tiny
BSCHRUM
  • MEMBER
  • 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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Monday, November 28th, 2011 AT 7:41 PM

11 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 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
  • MECHANIC
  • 52,797 POSTS
First of all, you missed the obvious. try changing the spark plug and I bet your issue with the 304 is gone
If not you will need to get a noid light to be sure the injector is getting pulse. If getting pulse,spark and has good compression the injector may be bad/not squirting fuel

See the guides below, they will help

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Roy
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Monday, November 28th, 2011 AT 8:12 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 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
  • 4 POSTS
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
  • MECHANIC
  • 20,758 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
  • 4 POSTS
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
  • MECHANIC
  • 20,758 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
  • 4 POSTS
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
Tiny
ZIPPYRAIN09
  • MEMBER
  • 2 POSTS
My 05 Chevy Colorado have the same thing about the driver window and the locks and there is no spark on cylinder 4 I tried a lot of stuff and nothing did you find out what was the problem? I think I’m gonna go for a computer and see what happens
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Wednesday, January 30th, 2019 AT 5:10 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
If you have a scope, you can check the signal from the coil to the PCM. You cannot tell with a voltmeter or test light.

Check the wiring back to the PCM from the coil.

https://www.2carpros.com/articles/how-to-check-wiring

Roy
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Wednesday, January 30th, 2019 AT 5:26 PM

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