Is it finally toast? (Very high mileage cylinder misfire)
 

Hey everyone,

First off, I want to thank everyone for the awesome resource that this site is, and for all the individual help I’ve gotten over the years.

Current problem: I have a 2003 sedan with 310K. A couple days ago I was driving to work and the check engine light began to flash. I pulled over and had my OBD2 with me at the time and pulled a P0303 (cylinder 3 misfire). I drove home and used a different car for the day. I got home later and replaced the spark plugs. This is where the bad news starts.

Cyl 2: Plug well is full of oil. Plug needs replacing.
Cyl 4: Plug needs replacing.
Cyl 6: Small amount of oil, Plug needs replacing.

Cyl 1: Plug needs replacing.
Cyl 3: Plug looks awful. Threads are rusting badly.
Cyl 5: Plug looks awful. Threads are rusting badly.

Removed as much oil as I could from 2 and installed new plugs. Engine is still misfiring on one of the cylinders (likely 3?)

I’m curious if this situation is worth further pursuit. In any case, can’t be mad about 310K.

New valve covers, new plugs and new coil packs followed by a compression test are in order. But, don't know what else might be wrong on a 300K motor.

Thanks. I’m gonna first swap the coil packs to see if I pull a new code.

As long as the compression test passes with less than 10% variance between the highest and lowest measurement then the motor is technically still ok. I would expect an average value of about 150 on a motor with that many miles. I would also expect many other mechanical failures in your future due to the mileage but congrats on breaking 300k with that engine!

When doing the compression test make sure the engine is warm and to rotate the motor 7 times per cylinder, it's easiest to have someone else crank while you watch the gauge.

Be sure to pull the fuel pump relay and run the engine till it stutters then quickly pull coil packs/plugs, then do the test. Since you're pulling plugs hot I would STRONGLY recommend you use anti-seize on the plug threads to prevent stripping the heads, don't apply anti-seize to the first 3 threads that engage the head or it can get into the combustion chamber.

Swapped the coil packs from 3 and 5, and low and behold we now have P0305. I assume this is good news and she might live another day.

There’s really no reason I couldn’t have figured that out without posting, but isn’t that always how it works?

Only fools are afraid to ask for advice.

Good advice! I had oil in [B][I]ALL SPARK PLUG WELLS. Replaced the valve covers and plugs after cleaning the mess up. Runs like a champ. Burning oil smell remains. But I know it will disappear shortly. 95K Covers are expensive!