Cylinder 2 Misfire Help

F

FenderBender

Member
Friday night my 2009 Rubicon felt sluggish, was running really rough, and had a persistent check engine light flashing on the 5 mile drive home. Using the built-in code display, the code was p0302 indicating a cylinder 2 misfire.

I knew that my spark plugs were old (95k miles), so I replaced all plugs and wires yesterday. Still basically the same symptoms.

I haven't replaced the coil pack. I figured I'll do this next. Should I just get a Mopar replacement? Any advantage to other "performance" variants, or is that asking for trouble/waste of money?

I will also add some Red HEET in case my fuel is bad and it should also act as an injector cleaner.

Besides that, what else should I be looking at?

Thanks for and advice.
 
A flashing light means the cat is at risk of being damaged. It's more likely a fuel issue (like injector dumping fuel into a cylinder). Although a misfire from the ignition system will cause some raw fuel to leave the cylinder, it doesn't typically cause a flashing light. That's been my experience anyways. So it just randomly started out of nowhere?
 
I should specify that the check engine light flashes while it's on, then it'll stop flashing and disappear totally. There hasn't been a solid light since replacing the plugs and wires, though it drives the same.
 
FenderBender said:
I should specify that the check engine light flashes while it's on, then it'll stop flashing and disappear totally. There hasn't been a solid light since replacing the plugs and wires, though it drives the same.
Click to expand...

Check all of your wiring to your coils and injectors. Look for signs of rodent damage, rubbing, etc. Also check your PCM harness in the same way. Any chance your plug wire is resting on exhaust? Strange that a flashing Engine light would go away.
 
Looks like I accidentally deleted my first response when I tried to edit it. Oops. Curse my fat, stubby thumb.

What you say about a flashing light matches what the owner's manual says.

My issue started seemingly out of nowhere. It was 10-30 miles after filling up, which is why I was wondering if it's fuel related. I did take this tank to pretty darn close to empty. I wonder if the fuel at the bottom of the tank had some gunk in it and clogged something...

The curious thing is that the check engine light will only come if you put the car under load. Then the light comes on and flashes. If you idle for a minute or two, the light goes away.
 
WJCO said:
Check all of your wiring to your coils and injectors. Look for signs of rodent damage, rubbing, etc. Also check your PCM harness in the same way. Any chance your plug wire is resting on exhaust? Strange that a flashing Engine light would go away.
Click to expand...

These are good ideas. I'll check this week once there's daylight. I haven't looked into the injectors at all, so I can't even guess how the wiring is.

The plug wires don't touch the exhaust. The plug wire to cylinder 2 is super short, so there isn't much slack for it to bend into the exhaust.
 
Its a misfire.
Spark
Fuel
Air
Compression

You don't have one of these intermittently. You can pretty much rule out Air/compression as its not a constant misfire. Its not uncommon for the light to only flash and then go away.

I wouldn't say its bad fuel because its only one cylinder. You replaced plugs and wires but didn't verify if you have good spark or not. Did you use dielectric grease on the ends? Does it only misfire when its raining/wet out? Start it up and spray the coil with a hose and see if it starts doing it.
As WJ mentioned check your injector wiring harness. if all looks in tact swap the injector to a different cylinder and see if the misfire moves to the other cylinder.
 
I had this same problem when I got some bad fuel. Put a couple bottles of Lucas heavy duty fuel cleaner in the tank and drove slow until it cleared out. The next couple tanks I used premium Chevron gas and one bottle of Lucas and it's been fine ever since.

Not saying the others are wrong, but if it happened right after a refuel, there's a good chance this happened to you as well.



--
Build Thread - Adventures of Fiona - https://wayalife.com/showthread.php?t=47407
 
Quick update on this.

The problem happened when it was dry, but cold (no rain or snow). Once the weather warmed up, I replaced the coil pack since it was so easy to get to. I also added injector cleaner to the tank and applied dielectric grease to the both ends of the wires since I forgot originally. One of those things fixed it. No more misfire.

I suspect the coil pack had gone bad. I was pretty careful with connections when I did the spark plugs, so I don't think re-plugging them in did it. If the fuel was bad or the injectors were dirty, I would expect some time for clean fuel to move through the lines and clear up the injectors. However, as soon as I put in the coil pack it ran smoothly.

Thanks for all the help and advice! Now my Jeep is back up and running.
 
I would bet the lack of dielectric grease was the root cause, especially since you said it was happening in cold dry conditions. Glad you got it resolved.


Sent from my iPhone using WAYALIFE
 
Noble Woodsman said:
I would bet the lack of dielectric grease was the root cause, especially since you said it was happening in cold dry conditions. Glad you got it resolved.


Sent from my iPhone using WAYALIFE
Click to expand...

Maybe someone can educate me here. I thought that the purpose of dielectric grease was to seal out moisture and other sources of corrosion (also keeps things from sticking together so later maintenance is easier). It's dielectric, i.e. not a good conductor, so it doesn't make connections any better. In fact, if you put dielectric grease between the metal contacts of any connection the resistance between the two go up.

So then how would a lack of dielectric grease cause the misfire with new plugs and wires? If you mean that not having dielectric grease on the old plugs and wires, then I agree that could cause things to age and wear faster.
 
I had the same issue driving back up to the nw for Christmas hauling the trailer under load. Happened once on the way up, and once on the way back down. Blinked a couple times then went away as I crested a rise. No rough idle or anything.


Sent from my iPhone using WAYALIFE
 
FenderBender said:
Maybe someone can educate me here. I thought that the purpose of dielectric grease was to seal out moisture and other sources of corrosion (also keeps things from sticking together so later maintenance is easier). It's dielectric, i.e. not a good conductor, so it doesn't make connections any better. In fact, if you put dielectric grease between the metal contacts of any connection the resistance between the two go up.

So then how would a lack of dielectric grease cause the misfire with new plugs and wires? If you mean that not having dielectric grease on the old plugs and wires, then I agree that could cause things to age and wear faster.
Click to expand...

Yes it's an insulator, not a conductor and is designed to prevent corrosion.
 
FenderBender said:
If you mean that not having dielectric grease on the old plugs and wires, then I agree that could cause things to age and wear faster.
Click to expand...

Yes, this is what i meant, but re-reading your posts, i realize now that this was not your situation.


Sent from my iPhone using WAYALIFE
 
You must log in or register to reply here.
Top Bottom