How to fix a misfire?

[Clement]

2002 Hyundai Accent, 1.6L

Engine light turned on yesterday, went to Autozone, they hoocked up the odbc reader and it said that I have a misfire on cylinder 3.

The plugs are NGK v-power and have less than 10K on them. Should I just change the wires? What is the effect of a misfire? I never noticed rough running or idling, or lack of power. If I was running on 1.2L I would know it.

 

[Matt_S]

Wires would be the next thing I'd try. Get a good set, too, not a cheap one, or you'll have the same problem in another 10k. If the car has a distributor, do the cap and rotor, too. I made the mistake of replacing plugs on my wife's Honda at 40k total vehicle miles without doing wires, cap and rotor, too. Guess what happened?

 

[TheLoneRanger]

Today's OBD II systmes will trigger a light if the ECM detects 2 misfires during 2 consecutive starts (on the same cylinder). That means you can have a misfire that's not detectable during normal driving.

The misfire can be caused by the plug, wire, or coil, or possibly a bad wire connection. Like Matt says, replace the wires and the plug on that particular cylinder first. Chances are that will fix it. If you have the coil-on-plug system, just replace the plug.

 

[kenw]

by all means, just pull the plug itself first. It may just be fouled. Now as to WHY it's fouled, that's phase 2...

but before you spend $100 on new wires, make sure same gunk isn't fouling the plug. It happens.

 

[Clement]

I checked the plug, it looks fine, no noticeable wear, no buildup, a little bit of white stuff on it, but the electrodes are in good shape.

It has a solid state system, no moving parts in the distribuitor thing. New wirea were about $37 at Advance Auto.

I did pull the plug, and played with the wires a bit. I think I'll have to clear the ECM memory to see if it is still picking up the misfire. I may wait until it warms up a bit first!

 

[punisher]

Are the NGK-V Powers the factory replacement plug? If not, then put in what the owners manual says to, gapped at the correct specs. That is 90% of the misfire codes. Not going to relate my experiences with Bosch plugs and FoMoCo vehicles.

If you have COP (coil on plug) ingnition, you can also swap coil packs around and see if the misfire code follows the coil pack, same for plugs, move it to a different hole and see if the misfire code changes. Not elegant, but it works when you don't have a bay full of diag equipment.

 

[1 FMF]

if your in upstate NY, I'm guessing it's pretty cold up there. It is here. Maybe just a one-time thing due to the cold? You said the engine light only turned on yesterday. I would wait and see if you get more misfires. May have also been some water passing through the system. More misfires on other cylinders might suggest my theory. More on the same cylinder would hint more towards the plug, since it may not be the OEM plug like said. Since its a 2002, I would think it unlikely it's plug wires unless you have something like 70k miles on the odometer. ALthough since you changed the plugs, you might have damaged the wire pulling/reattaching it. Try switching the wire to a different cylinder if possible, if the new cylinder misfires then you know.

 

[tmorris1]

It may not be missing now. At the time the light turned on the computer probably tripped the light because it sensed some number of misfires on that cyclinder. Could be from wires or spark plug, or it could be from an injector that got some crap in it for a short time, and is now fixed.

 

[Clement]

The code is gone, light went off yesterday afternoon. My playing with the wires may have fixed it?

The NGK V-power are the oem replacement and are pre-gapped. Actually, the car came with Champion copper, which I replaced with Bosch platinum, which were shot after 15K miles, which I replaced with the NGK.

And oooh yeah, it is cold up here, 4 below this morning.

 

[crossbow]

Be wary...sometimes OBD-II's will throw false misfires. Sometimes its just a PCM calibration issue and is fixed in a reflash of the car's PCM. Visit the forums for your particular car and check the TSB's (technical service bulliteens) to see if its a computer related problem.

The mazda6, a can enabled car, has two reflashes for false misfire codes. Even after the reflashes, there is stilla false misfire code which is caused when you hammer on the car when the coolant is below 160F. Its basically a dealer flag for owner abuse.