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DBranch, ASE Certified Technician
Category: Car
Satisfied Customers: 706
Experience:  Factory trained Silver Certified Land Rover Technician. 7 years of automotive experience.
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2004 Hyundai Accent: a misfire in cylinder 4 that I..exhaust..rpm

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Hi, I'm trying to troubleshoot a misfire in cylinder 4 that I'm getting in my 2004 Hyundai Accent. I can feel the engine vibrate and the exhaust backfires a little. The ECL also flashes, but it seems like the problem only happens at idle and always on cylinder 4 and when I bring the rpm's up to about 1500 to 2000 the ECL stops flashing and the engine smooths out. I replaced the sparkplug wires, because I found wire 4's insulator was chaffed and when I disconnected the sparkplug wire to check for spark I could see it arc at the ignition coil sparkplug connector. That didn't seem to fix the problem however. Previously I also changed the #4 fuel injector and all spark plugs. I checked the resistance at the primary and secondary coils and they appeared fine. I have done everything I could think of outside of a compression test. Also, I did find on the primary ignition coil connector, the clip is missing so it doesn't snap into place, but I would think if that was the problem I would be having missfires on cylinders 1 and 4. I had the engine replaced almost a year ago and it has 1 year warranty on it so I'm trying to avoid bringing it to the dealer and paying outrageous repair costs unless I can narrow it down to a fault that would be covered under warranty. But any help you can provide would be great, because I'm out of ideas.

Welcome to JA.


You might have a head gasket leak. Do you ahve any sigsn of a leak. Is your coolant level low. Look inside the oil cap to see if you see any creamy milky substance. The only misfire code you are getting is for cylinder number 4. The reason the check engine light flashes meaning there is a catalyst damaging misfire.

Customer: replied 7 years ago.
I just checked the oil and looks good, no creamy milky substance. Coolant also looks nice and green and isn't low. Would a head gasket leak cause just one cylinder to misfire? I was leaning on doing a compression test, but I don't have a tester so I didn't want to pick one up unless I needed to. Also, I do only have one O2 sensor, because I had a custom header installed 3 years ago so I only have the downpipe sensor installed. As I haven't had any misfire problems until recently and only one cylinder is misfiring, you don't think that could be a possible cause do you? But if you are leaning towards an air leak problem and not a fuel or spark problem then I'll pick up a compression tester.

Yeah you could have just a leak in one spot on the head gasket. Also look at the spark plug when you pull it out to see if it looks steamed cleaned that means that possibly coolant is leaking into the cylinder. You will have an o2 sensor in front of the cat and one behind the cat to monitor making sure the catalytic converter is doing its job. Its sounds like you have covered everythingelse so I would get a compression tester.

Customer: replied 7 years ago.
Hi, sorry for the long delay in getting back to you. I checked the compression in cylinder 4 and it was perfect according to manufacturer specs. I went back to check the spark again and I did notice when I disconnected #4 spark plug wire and checked for spark it started feeding back to the ignition coil connector and arching at the spark plug boot (near ignition coil) to the engine. I checked #1 and it didn't do that. Not sure if that has to do with wire length or not. Am I grasping at straws or could the ignition coils still be a likely cause? When I get a chance I'm going to try one more compression test as I didn't check it with the engine fully warmed. Outside of those two options I'm not sure what else I could possibly check.

I am not sure exactly what I mean tell me if I am wrong. If it is arcing out of the spark plug wire at the boot on the coil then the boot may be split. arcing you could try switching the wire and a coil to a different cylinder to see if the misfire moves. Do them one at a time so you know what the problem might be.

Customer: replied 7 years ago.
The sparkplug wires are brand new as I did change the wires, because the 4th wire's insulation was chaffed. I was going to swap ignition coils, but they have keyed connectors. Will swapping the spark plug wires to different coils cause any problems? As I'm not a car tech, do the ignition coils send sparks to each wire at a certain interval or does it even matter which wire goes to what coil connector? Heck I'll try it right now to see if I have a coil problem. Hopefully the cables are long enough. After that, unless you have any other advice I'm not going hold you up any more and Accept your answer.

The wires are different lengths you can switch them it is not going to mess anything up. I appreciate it. Let me know if you have anymore questions and please leave positive feedback. Thanks again

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