guster900

So after getting my car back today from getting the front bearings done, I get a CEL on the way home. Drive over to auto zone, and it has multiple cylinder misfire codes. They suggest the usual, plugs, wires, water in the fuel. So, I get new NKG plugs, gap them to .044. Put in the new wires, reset the code. Drive about 15 miles, light comes back on. Go back, now it's just cylinder 2 misfiring. He thought it was bad gas, or some piece of dirt or something stuck in the injector. So he recommended some cleaner he uses, I don't remember the kind, but I put that in, and drove about 45 miles this time before the light came on. This time I didn't check the code, I just un-hooked the battery and reset it that way. This last time I drove it about 20 miles and it came on, and I'll have the code checked in the morning to see if it's still #2 misfiring.

So, I've read lots of threads, and know the order of things to look at or have checked. I did the plugs and wires, also cleaned the MAF sensor and put in a new air filter. Put fuel system cleaner in to try and clean up the gas and/or injector... although he said it wouldn’t work first time, I'd probably have to go through a couple tanks for it to work. So next on the list is the coil pack, correct? The guy at auto zone didn't think that was it because it was only cylinder 2 misfiring & not a pair. Although the first time multiple cylinders did misfire. Could the pack be bad if just one cylinder misfires?

Also, any ideas on why it's so random? I mean, 15, 20, 45 miles, never the same. Also, I can't tell any difference when I'm driving and the CEL is on. You would think with a cylinder misfiring you could tell, but it drives perfectly normal. Same power, same acceleration. If it wasn't for the light, you'd never know something was wrong, and I certainly wouldn't have guessed a misfiring cylinder since there is no change in performance. Would that point to any particular known cause?

Lastly, when a cylinder misfires and throws the code out, the CEL comes on. Does that mean it has just misfired once, or is it continually misfiring? Could it misfire once and then the light stays on until reset? Would that explain why there is no change in performance? I’m just not sure if that’s how it works.

Any ideas before I replace the coil pack?
Thanks

fury

The control module is programmed to run a few test cycles before throwing a CEL. In other words, when you get a CEL, it means that trouble was detected after several cycles. If it misfired once (as some sort of freak fluke) and went away, a CEL would not be thrown.

A cylinder mis-fire on our cars (4 cyl) CANNOT go by unnoticed. You'll notice the car shaking, and while holding the steering wheel, you'll see your arm as a blur. But you said that you didn't notice anything. So I'm wondering if it could be the primary oxygen sensor going bad??? Someone can confirm if this can throw a cylinder mis-fire code.

One other thing you might want to look at, is a vacuum leak.

guster900

Yep, I really don't notice anything when it is supposedly misfiring. I hesitate to think it is an o2 sensor because both were replaced 4-5 months ago, along with the cat.

It couldn't be the coil pack intermittently failing, being weak? Or a clogged up fuel injector? I hate the idea of a vacuum leak :-(

alice6

any chance you have the code that the reader received? the codes are vehicle specific and sometimes what autozone has doesn't exactly match the manufactures interpretation. if you have the code you can look it up on hmaservice and go from there.

guster900

Ok, I got new plugs & wires, and fuel cleaner in the gas. No help. At first it had multiple cylinders misfiring, but then just cylinder 2. Since just one was misfiring, I swapped out the fuel injectors for good clean used ones. After I put in the new fuel injectors it seemed to run great. But after 102 miles the check engine light flashed several times then stayed on. Now cylinders 1 & 4 are misfiring along with random misfire code. Reset the cel, and same thing after just three miles. There is no difference when this happens. It drives exactly the same, and even better then it used to with the new fuel injectors. It happens at what seems to be totally random miles 15, 20, 45 miles after resting the cel, now 102, and then 3. My only idea is to buy a new ignition coil, any other ideas?

fury

It's baffling that you're getting all of these cylinder misfires without any physical notice. Could be a bad ECU. The way I see it, if it truly were cylinder misfires, and ESPECIALLY that you mention 2 cylinder misfires (eg. cylinder 1 and 4), you would notice it for sure! No question!! There's no way you could run on 2 cylinders and feel like the car's running smooth. So, it seems to me that something's tricking the control module into thinking that it's a misfire, when in actual fact it isn't.

I'd still look at that secondary Oxygen sensor. I'm betting on it.

You can also try a leak down and compresssion test.

yamaha

I had this very same issue in my Elantra a few years ago. Turned out to be a bad coil pack. If you log into HMAservice you should be able to find the ohm readout for the packs.

guster900

Well I got to thinking about it, and the very first time the cel came on, it was cylinder 2 & 3 misfire. My brother was driving so I couldn't feel how it was driving. Then it was reset and #2 started misfiring only, and I changed the injectors. Now it starts missing on 1 & 4, so again a pair misfiring. I had drove home about 3 miles and didn't notice much, but when I went to drive it again, it felt off, rough, and for the first time thought I could actually feel the misfiring. Since two times it was misfiring in pairs, I decided to go ahead with the coil pack, and changed that this afternoon. I also put on new battery connections because the + seemed loose and I couldn't get it to stay tight. At anyrate, it's been a little more than 50 miles, and no problems yet. But again, it's come on at random miles up to 102. It drives perfectly fine though right now, and it seems if it was something with compression, it wouldn't drive so nicely for 50-100 miles before a cel. We'll see, but I'm keeping my fingers crossed it was the coil pack.

supercow

thats what I was thinking, its the only thing left! lol

hope you've got it worked out.