trouble code P0304

2005 CHEVROLET COLORADO

92,000 MILES

BSCHRUM

MEMBER
4 POSTS

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?

Nov 28, 2011 at 7:41 PM

WRENCHTECH

✓ASE Certified Mechanic
20,761 POSTS

Did you try swapping the plug with another cylinder too?

Take a compression test also.

Nov 28, 2011 at 8:10 PM

ASEMASTER6371

✓ASE Certified Mechanic
52,796 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

Nov 28, 2011 at 8:12 PM

WRENCHTECH

✓ASE Certified Mechanic
20,761 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.

Nov 28, 2011 at 9:04 PM

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).

Nov 29, 2011 at 3:55 AM

WRENCHTECH

✓ASE Certified Mechanic
20,761 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.

Nov 29, 2011 at 10:48 AM

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.

Nov 29, 2011 at 2:44 PM

WRENCHTECH

✓ASE Certified Mechanic
20,761 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.

Nov 29, 2011 at 8:03 PM

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?

Nov 29, 2011 at 10:24 PM

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

Jan 30, 2019 at 5:10 PM

ASEMASTER6371

✓ASE Certified Mechanic
52,796 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

Jan 30, 2019 at 5:26 PM

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