'03 Mountaineer 4.6 throwing P0304 and P0316... Thoughts?

[Frizzle Fry]

Just started throwing these two codes P0304 and P0316 (misfire cyl 4, misfire on start). Noticed some cheesy/milky film on the oil cap and in the tube, oil level low but oil is not milky on the dipstick (level was low, though).

I assumed it was the intake gasket, but sprayed a little starter fluid around and didn't notice any rev. It's time to replace the plugs anyway so I'm gonna do that, but I'm wondering if anyone's got ideass on where to go from here.

Thoughts?

 

[lincolnshibuya]

if you're over 100k, time for new plugs and cops. misfire should be fixed immediately because they'll kill your catalytic converters (expensive to replace)

 

[5whiskey]

Could be a number of things... but my initial guess is head gasket. If you have a misfire, it's fuel, fire, compression, or timing. You can probably rule out timing (being a 8 cylinder timing would affect all cylinders and all). Soo... fuel, fire, compression. Fuel would be a bad injector, fire would be a shot spark plug or wire, and compression would be the head gasket. The milky film on the oil cap is also not a great sign (meaning water has mixed with oil, classic sign of a blown head gasket), but there are other plausible explanations.

I would replace the plugs and wires and reset the code by disconnecting the battery ground. Drive it, if the code pops up again check the compression on all of the cylinders (especially cylinder 4). If the compression is out of spec, then you need to do some work on the heads. Or you could just drive it for now until you save up the money to do it, but I wouldn't drive it too long.

If you replace the spark plugs and compression is in spec on all cylinders, try replacing the injector.

 

[Frizzle Fry]

I'm gonna bang out the plugs and see what happens - cheap enough I get them at cost from work.

Oil on the dipstick is clear and clean, and there's not a lot on the oil cap just a little around the rim and dribbling down the side, making me think it COULD be just some condensation from the recent cold weather and the fact that I drive about 10 minutes to work and back these days. Fingers crossed.