Check Engine Light / Misfire

2004 CHEVROLET MONTE CARLO

65,000 MILES • 6 CYL • FWD • AUTOMATIC

DUSTIN W

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The check engine light is on in my car. It is usually on steady but when I accelerate it will usually start flashing. The car idles rough, and hesitates and stumbles when I accelerate. I checked it with a timing light and it showed the #3 and #6 cylinders are misfiring. I replaced the coil pack that those two cylinders link to but it did not help. Please let me know if you have any advice.

Mar 22, 2008 at 9:44 PM

JACOBANDNICKOLAS

CERTIFIED EXPERT
110,175 POSTS

Hi,

A misfire can be caused by many things. Areas of possible issues include an engine vacuum leak, worn spark plugs, a weak coil, low or high fuel pressure, low compression, and so on.

Here is what I suggest. The vehicle doesn't have many miles, so I doubt it is compression-related. Also, since it is the two specific cylinders, that takes me to the coil (which you replaced). The first thing I would do is replace the spark plugs. Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-change-spark-plugs

Additionally, if the spark plug wires are older, replace them as well.

If that doesn't resolve the issue, there is a chance it is related to the ignition control module (ICM). The ICM is what you attach the coils to. Remove the ICM and have it tested at a parts store. Most are able to do it and will, free of charge.

I attached the directions for the removal and replacement of the ICM below.

I hope this helps. Let me know if you have other questions.

Take care,

Joe

See pics below.

Images (Click to enlarge)

Jul 26, 2021 at 8:19 PM