Shatzy Posted August 10, 2015 Report Share Posted August 10, 2015 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 Link to comment Share on other sites More sharing options...
barczy01 Posted August 11, 2015 Report Share Posted August 11, 2015 Is the car misfiring all the time with a flashing engine light? Link to comment Share on other sites More sharing options...
Shatzy Posted August 11, 2015 Author Report Share Posted August 11, 2015 Car runs smooth, no misfire detected in performance. 18 MPG! Only msg on dash: "Check Engine Soon"! Link to comment Share on other sites More sharing options...
Shatzy Posted August 30, 2015 Author Report Share Posted August 30, 2015 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 Link to comment Share on other sites More sharing options...
barczy01 Posted August 30, 2015 Report Share Posted August 30, 2015 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? Link to comment Share on other sites More sharing options...
Shatzy Posted August 30, 2015 Author Report Share Posted August 30, 2015 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 Link to comment Share on other sites More sharing options...
Shatzy Posted August 31, 2015 Author Report Share Posted August 31, 2015 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 Link to comment Share on other sites More sharing options...
winterset Posted August 31, 2015 Report Share Posted August 31, 2015 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. Link to comment Share on other sites More sharing options...
rockfangd Posted August 31, 2015 Report Share Posted August 31, 2015 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 Link to comment Share on other sites More sharing options...
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