Hello all - I have a peculiar misfire I hope I can resolve with the help of your expertise. My bluedrive indicates code P0303 Cylinder 3 Misfire. Some things to note..I can floor it from park, without a misfire. However, say I'm going 50+ in 5th gear....and put even a little extra load on accelerating (I discovered the issue driving on a freeway when I was cut off and had to accelerate quickly), the misfire occurs and I have to pull over and shut the car off. If I drive it smooth on the pedal without major load it's ok...slightest bit of extra load and its misfiring hard.

Thank you in advance,

AC

 

Sounds like an ignition coil. What's your mileage? These things tend to go at 200k.

 

Just about to hit 240K. Do you know why this only happens when I'm at higher speeds putting a lot of load on the car?

 

Plugs and or coil.
I was going through coils like mad at one point, till
a mechanic told me, more likely the plugs.
Old plugs stress the coils.
Don't figure on more than 50K miles on stock plugs (the GOOD iridium plugs sold by MB and made by NGK and you can buy from NGK much cheaper),
15K for copper or 30K for iridium IX (cheap version NGK iridium).
So, now, I have no problems.
Move the coil to another cylinder and see if the problem moves with it.

 

Bottom of Coil
So I took off the coil of cylinder 3 (misfire). The bottom where it slides into the spark plug doesn't look too healthy...or maybe this is healthy. I took the coil of cylinder 2 out and it was substantially cleaner(only a tiny bit of gook). Guessing that's oil which could be linked to why I'm burning it so fast (I add about a quart every 2 months). I drive about 550 miles a week.

 

@slammer111 , if possible, a second opinion of how to move forward would be much appreciated.

Thanks!

AC

 

No reason why that stuff is in there. Maybe some mechanic got that stuff in there by accident? It's an electrical contact. The spring should be bare.

Remove all that guacamole and also clean the metal terminal of the spark plug. Add some dielectric grease to the ceramic spark plug base (watch a video online to make sure you're doing it properly), and reinstall ignition coil.

 

Certainly didn’t seem like it belonged. I removed that residue and swapped the coil. Misfire in 3 continues. I then pulled the plug out of 3, which had some white on the spark indicating it possibly was running lead in that cyclinder. I swapped the plugs of 2 and 3 and boom, misfire moved to the other cylinder.

 

There you go! Time for plugs.