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I continue to get error code indicating engine misfire, cyl #4. Replaced, plug, boot, AND front coil, but msg returns. This has been going on for several thousand miles.

Car runs fine, 18 mpg, regular gas. What harm can this do to engine?

Steve M

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  • 3 weeks later...

Engine Misfire Code Continues: 2000 DeVille:

Misfire Code on Cyl. #4 persists. I would greatly appreciate any advice offered to resolve this problem.

I'm particularly concerned about the long term affect this Code/Condition will have on the vehicle, even though it continues to run smooth, and maintains great gas mileage!!!

Have replaced front coil, and Cyl. # 4 plug, boot and wire to no avail.

If I clear the Code, it will only be 5 - 10 miles before it will reappear and remain until I clear it again!

If no response from members here, looks like I'll be forced to take car to the dealer.

Steve M

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swap the plug and boot with #6 cylinder and see if you can get the misfire to move. Have you run a compression test on that bank?

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I've already swapped the plug and boot out with another cylinder; Code returns. Have not run a compression check; I'll need to find someone to do that for me before I resort to a dealer.

Thanks much.

Steve M

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Would again like to inquire what harm can be done to engine as a result of ongoing engine misfire

Code? Condition has existed for quite some time, but car continues to run fine.

SteveM.

Maryland

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Over time, a misfire can damage your cat by melting the substrate. Unburned gasoline will go to the cat, overheat and burn the honeycomb. When this happens, the post 02 sensor will throw a p0420 code. Actually, a plugged cat can also be a cause of a misfire if the misfire happens on acceleration under load. Also consider an additive in the oil to help free sticking valves so you are covered there as well.

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Inspect the plug to the coil pack module making sure all pins are seated properly, check wiring to see if there is any chaffing under the beauty cover.

I recommend hooking up a scantool and watching the misfire status of each cylinder.

I had a similair problem and I verified the cylinder was actually getting spark by replacing the boots with wires and setting the module atop the engine,

I then added a inline spark tester and ran the engine.

My problem was 2 bad coil pack modules in a row. Bought a brand new one and it was damaged in transit. Last one nailed it. Ran like new

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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