1998 Cylinder 3 Misfire

I bought a 1998 3.4 Toyota 4Runner with 284,000 miles last week, and I’m dealing with a P0303 misfire on cylinder 3. I’ve replaced the spark plugs (OEM), ignition wires (NGK), and swapped ignition coils, but the issue still persists in cylinder 3. The spark plug in cylinder 3 is somewhat greasy and oily compared to all the other plugs, the threads are also much cleaner looking comparatively, the ceramic area also showing signs of oil contamination. I’ve noticed that the engine light will flash typically under hard acceleration, but then it goes away on its own after a bit. I can also feel more of a shake when the car is in gear idling compared to in park. Compression on cylinder 3 is solid at 190 psi, so I don’t think it’s an internal engine issue. Could this be caused by oil leaking into the spark plug well from a bad valve cover gasket or possibly worn valve stem seals? Has anyone experienced something similar or have suggestions on how to fix this?

 

First off; thats the wrong plug.
You need to use the dual electrode plug. Dont use the 4 prong plug either I was offered a set and burned all the prongs off of one.

Second; I had this same cylinder and code, it was an injector.

 

Its a 6 cylinder right? Those plugs look good even though there not the correct dual electrode.

 

These were the plugs that were in, I just replaced them with the correct dual electrode plugs from Toyota and still have the same issue.

 

Yes 3.4 engine. Is there anything to be concerned about with the plug from cylinder 3 having the ceramic being black from oil and all the other plugs are white? Or could this be a cause from the injectors?

 

its not that bad really. But wrong plug.

 

Does not look like the crush washer even flatened. To tighten plugs use a wrench and tighten the threads until stops with your fingers. Then using the wrench tighten:
11:00 am to 3:00pm
11:00 am to 3:00pm
then 11:00 am to 1:00pm
You will feel it tighten and compress the crush washer on the plug.

 

Ya I would say the "cleaner" threaded plug was not combusting at all?
Vote: injector


You might want to do all six and new pig tails.

 

When I replaced all 6 plugs I torqued them to 13 foot pounds per the spec. After driving around for a few minutes I pulled the new plugs back out and noticed the spark plug in cylinder 3 doesn’t have any change in color due to the heat like the other 5 plugs. I’m guessing the fuel injector is bad like you said.

(Cylinder 3 spark plug is on right, notice the diode doesn’t have the coloration like the other plug)