Random / Multiple Cylinder Misfires

[Grusvag]

Got some stumbling under medium to heavy throttle and have a few OBD Codes as a result.

P0300 Random / Multiple Cylinder Misfire
P0302 Cylinder 2 Misfire
P0304 Cylinder 4 Misfire

Has been doing this for a while now.
Any thoughts as to what might be causing it?
Bad coils?

Thanks in advance.
John

[Andrew149]

Replace the plugs and coils.


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[Grusvag]

Thanks.
[up]

[EvolutionArmory]

Swap coil 2 with 1 and 4 with 3 and see if the misfires move first.

Why? Because what if it isn’t coils? Now you just spent 100 bucks on coils and still have a misfiring car if it isn’t the coils 😀

[Jet08]

As an example I had very similar misfires which were carbon on the injectors, others have had bad wiring on the coil harness so test check by moving the coils between cylinders before spending on parts that may not be needed.

[Grusvag]

Great idea - will swap coils around and see what happens. Thanks!

[Grusvag]

Interesting.
Swapped the coils around (#2 to #1, and #4 to #3) and one of the misfires moved, one didn't. Now 3 and 4 have a misfire.
Maybe it's a combination of bad coils and bad plugs?

Think I'll go ahead and replace all coils and plugs and hope that clears everything up.

[EvolutionArmory]

Interesting.
Swapped the coils around (#2 to #1, and #4 to #3) and one of the misfires moved, one didn't. Now 3 and 4 have a misfire.
Maybe it's a combination of bad coils and bad plugs?

Think I'll go ahead and replace all coils and plugs and hope that clears everything up.

Or maybe it has absolutely nothing to do with coils since swapping 3 and 4 had both cylinders misfiring where only one was misfiring and has everything to do with carbon build up.

Does the misfire only happen when you first drive it and clear up once driven a few miles? Or only misfire when under full throttle? A coil will misfire all the time when it’s bad. Misfires due to carbon build up are far more random where a bad coil isn’t.

[Grusvag]

The misfire is pretty much always there - doesn't seem to clear up after time. And it's not necessarily under full throttle, can be partial.

[EvolutionArmory]

So now move coil 3 and 4 to 1 and 2. If they both follow, you know you need coils. If they stay, you probably need a carbon clean or injectors.

Checking for misfires and swapping coils around is best if done on the same day.

[Grusvag]

I'm a little confused. If 2 and 4 misfired originally and I swapped them with 1 and 3 respectively, wouldn't 1 and 3 misfire now? Don't understand why 4 keeps misfiring and 1 doesn't now.

Moving them again is a good idea though. Will try that next.

[EvolutionArmory]

That’s exactly what I’m saying dude. One followed and one did not. You know 3 and 4 are misfiring right now. Move them to 1 and 2. If it follows, you at least need coils. If it doesn’t, you’re probably looking at carbon build up or injectors.

[Grusvag]

That’s exactly what I’m saying dude. One followed and one did not. You know 3 and 4 are misfiring right now. Move them to 1 and 2. If it follows, you at least need coils. If it doesn’t, you’re probably looking at carbon build up or injectors.

[up]
Thanks. Will swap again and see what happens.

[Grusvag]

Went ahead and replaced all spark plugs and coils. Drives like a new car! :-)