Stubborn P0304, P0306 Misfire on Cyl 6

[Ph03n1x24]

2005 Toyota 4runner Sport Truck V6 ~245,XXX miles

CEL P0304
Tejas Toyota Dealership in 2018 @ ~119,XXX miles
- Replaced plugs
- Replaced coil on cyl 6
<<< Problem solved >>>

Fast forward to today: 2023 ~245,XXX miles

CEL: P0304
- Replaced all spark plugs w/ NGK 6619 Iridium Spark Plugs
- Replaced all 6 coils

Ran great for a week or two then the P0304 code came back.
- Went back and retorqued the spark plugs to 13 lbs.

After a few days it's back again... IDEAS?

Checking the wires and boots later this evening.

Any ideas where I should look next? Injectors?

 

[OopsIBrokeIt]

2005 Toyota 4runner Sport Truck V6 ~245,XXX miles

Any ideas where I should look next? Injectors?

Ever done the head gasket? 03-05 V6s are known to have a flawed head gasket design that commonly results in cyl 6 misfiring.

Are you low on coolant or seeing signs of it pressurizing the system? Or have you had the coolant tested for exhaust gases?

 

[Ph03n1x24]

Ever done the head gasket? 03-05 V6s are known to have a flawed head gasket design that commonly results in cyl 6 misfiring.

Are you low on coolant or seeing signs of it pressurizing the system? Or have you had the coolant tested for exhaust gases?

No issues thus far with the head gasket but now you have me thinking.

I am not low on coolant but will check it again. Other than the cel and the occasional rough idle on a cold start it's running great.

I guess I need to bite the bullet and take it back into the dealership and have them check the head gasket and coolant.

Thanks for the input!

 

[Buckaroo]

With the engine running, do a wiggle test on the wiring and connector on #6 coil. Disassemble and visually inspect the wiring, the connector and the coil boot (look for tracking). Even though you just replaced the coils and plugs, I would swap the plug in 6 to another cylinder and the coil to a third cylinder. See if the misfire follows them. If not, the injector is the next obvious place to go. Visually inspect wiring and connector. Swap the injector on 6 to another cylinder and see if the misfire follows it.

 

[Ph03n1x24]

With the engine running, do a wiggle test on the wiring and connector on #6 coil. Disassemble and visually inspect the wiring, the connector and the coil boot (look for tracking). Even though you just replaced the coils and plugs, I would swap the plug in 6 to another cylinder and the coil to a third cylinder. See if the misfire follows them. If not, the injector is the next obvious place to go. Visually inspect wiring and connector. Swap the injector on 6 to another cylinder and see if the misfire follows it.

Thank you. I will do this over the weekend and report back on how it turned out.

 

[waypoint]

P0304 is a misfire on cylinder 4, so there's something to consider in your troubleshooting.

 

[Ph03n1x24]

P0304 is a misfire on cylinder 4, so there's something to consider in your troubleshooting.

UPDATE: P0304 & P0306 Correction from original post.

Further troubleshooting I noticed something I hadn't seen before now. Green gook on a couple connector pins for No. #4 cylinder and No. #6 Cylinder.

Ordered some new coil wires. (I hope this rectifies the problem)

Will update once I swap those out this weekend.

Also, my memory wasn't as good as I thought it was regarding my original issue. Seems there was more going on back in 2019.
Here's a copy...

 

[Ph03n1x24]

UPDATE: P0304 & P0306 Correction from original post.

Further troubleshooting I noticed something I hadn't seen before now. Green gook on a couple connector pins for No. #4 cylinder and No. #6 Cylinder.

Ordered some new coil wires. (I hope this rectifies the problem)

Will update once I swap those out this weekend.

Also, my memory wasn't as good as I thought it was regarding my original issue. Seems there was more going on back in 2019.
Here's a copy...

UPDATE: 05/17/23

Soooo, sheepishly I must admit I may have over complicated the issue. I was unable to get around to replacing the coil wires due to unexpected company and a heavy t-storm w/ subsequent power outage that hit us last weekend, here in the Houston area.

I did manage to top off the fuel tank last friday and by the time I got home from work on Monday the CEL was gone and it was running like a scalded ape. Then it dawned on me that right after I'd re-torqued the plugs I added a bottle of SeaFoam to a full tank of gas. That got me thinking, and then researching online. Duh, turns out it's rather common for SeaFoam to cause a cylinder misfire as it's doing its job.

So far so good! I will still change out the coil wires when I can as a preventative measure.

Thanks for all the great advice! This forum rocks!

Mark