Mechanics

HUNDAI ACCENT BLINKING CEL (P0304 CYLINDER 4 MISFIRE)

2001 Hyundai Other

Hello, I have a 2001 Hyundai Accent, 1.6L with 96k miles. The Check Engine Light has started blinking at idle, so I had the code checked. It is P0304 cylinder 4 misfire. The car does sound like it's missing at idle/low rpm (< 2000 rpm), but sounds fine at higher rpm. The CEL stops blinking at higher rpm, but blinks again at idle.

I have replaced plugs, wires, and coil pack with no success. Any ideas on what the problem could be?

The timing belt did break around 89k mi, and the head was reworked & at least some valves replaced. The car seemed to run fine thereafter, with the exception that the engine was difficult to turn over when starting after the engine was hot (sounded like a weak battery, but I replaced both battery & starter without success). This problem seems to have dissipated with time. Don't know if any of that's relevant to the current problem or not.

Thanks for any advice,

John
Avatar
Johnbanks
October 19, 2007.



Sounds like a weak injector, cant give the necessary fuel during low engine rpm's, but at higher becomes unnoticeable

Tiny
Jack42
Oct 19, 2007.
Hi Jack,

thanks for the response. So would you recommend replacing the injector? I've heard of having the injectors flushed. Is that a possible solution in this case, and if so, is there much cost savings in that route vs. Replacement? Or maybe that's only good for a clogged injector, and not a weak one?

Thanks again,

John

Tiny
Johnbanks
Oct 19, 2007.
Cleaning is like putting a band-aid on a bullet hole. Replace the #4 injector and enjoy your smooth running car

Tiny
Jack42
Oct 19, 2007.
Here's the latest. I took the injectors out to replace the #4 injector, but the Auto Parts store didn't have any in stock, and would take a few days to get. So, I went ahead and swapped injectors #3 and #4. Started it up, and it exhibited same symptoms. Took and had the codes read, and got P0304 again. I asked them to reset the codes, so I could be sure this wasn't just left over from before. After the reset, even though the CEL would blink during idle, it would extinguish during normal driving. This continued until I got home, and later took it for another drive. After the CEL blinked during idle again, the CEL came on solid during normal driving, just as before. Had the code read again, and again got P0304. So, it would appear the injector is not the problem.

I tested the coil pack with everything disconnected per the hmaservice. Com site, and compared the readings to the specs. For the secondary coil resistance, between terminals 1& 4 and 2& 3, I read 14.5 kOhms vs. The 10.3-13.9 kOhms specified. For the primary coil resistance, between terminals 1 & 4, I read an open vs. The 1 Ohm specified. I suppose this is indicative of a problem, but I am skeptical since I did temporarily replace the coil, but changed it back immediately after seeing the same symptoms at idle. The car was still missing at idle, and the CEL blinking. I did not drive the car at all with the new coil, so perhaps the ECM needed some time to reset?

Do you think this is the problem, or do you have some other suggestions?

Tiny
Johnbanks
Oct 21, 2007.
Have seen both coil and injector need to be replaced at the same time. If th einjector is weak, it can make it harder for the fuel to burn, raising the resistance in the coil that is trying to fire in an fuel lean environment

Tiny
Jack42
Oct 22, 2007.
I've been traveling, but had a chance to look at the car again last night. I began just by checking the compression just to completely rule out any mechancial issues. Everything there looked fine, but after I put everything back together, I cranked the car again to make sure it ran as before. It had become very dark by that time, and I noticed that as the car was idling, blue sparks were coming from around the body of the coil to the metal mounting frame. If I opened the throttle up, the sparks disappeared. This would be consistent with the car running rough at idle, and smoothly at higher speed. When I add everything up above, it seems to clearly point to a coil problem, but I'm skeptical since I had temporarily replaced the coil earlier, and noted no difference. As I mentioned, I did immediately remove the new coil after noticing no difference at idle, so perhaps it needed more time to run to correct the condition? Does this sound feasible to you?

Tiny
Johnbanks
Oct 25, 2007.
Check the plug for cracks or possibly an incorrect gap. If changing the coil made no difference at first, the plug may be causing excessive resistance in the new coil. When the plug is out, compare its color to a know good firing cylinder.

Tiny
Jack42
Oct 26, 2007.
I would without a doubt change the wires 1st, Pull the NO4 plug and inspect it for any abnormal conditions, if the wires dont cure the issue than its deffinately the coil. Good luck

Tiny
Turbotuff20g
Oct 27, 2007.
Im sorry I missed the point that you already switched the wires. Had a rough night lol. I would go with checking or replacing the spark plug as stated above but from my experience with being a Hyundai technician it sounds like that coil is bad, try spraying some water on it while running and see what effect that has if the coil arcs more and the misfire gets worse I would really reconsidering putting the new coil back ito the vehicle

Tiny
Turbotuff20g
Oct 28, 2007.
Hi, thanks for your response. I had already put in a new plug, to no effect. So, for my last test, I took and swapped the coil outputs to the #1 and #4 cylinders, ran it for a while, and then had the codes read again. My thinking was that whereas before I was consistently getting P0304, I should now see P0301 appear. Sure enough, this was the case, and in addition to the stored P0304, I now got a P0301, as well as a P0300 (random misfires), and a P0303. I attributed this to coil degradation, and will install a new coil. I hope my logic here was sound. I figured since the #1 and#4 cylinders fire together, all else should be equal. Does that make sense?

Thanks again,

John

Tiny
Johnbanks
Oct 29, 2007.
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