UK - Fiesta 2001 1.25 P0302 Cylinder 2 Misfire Detected

Question

My little car is running roughly. Mainly during acceleration once at cruising speed say 55mph is fine, just the odd little "cough". The second you try and accelerate it isn’t happy and loses power. The only way to keep or regain the speed is to VERY slowly accelerate. If you floor it the engine warning light flashes and goes off when you come off the pedal.

I connected my Maxiscan MS509 to the car today =, no major codes but a pending code of “P0302 Cylinder 2 Misfire Detected”. From my knowledge, this could be as simple as a plug/Lead failing (I don’t know when the plugs where last done in this car (if at all).

But could this be the Coil pack as well?

The car has recently shown “Catalyst Bank 1 below threshold” which I am confused about – is this the CAT or one of the Sensors? Both sensors (1 and 2) are showing good quick variations on the scanner. The car is 16 years old, and done 90,000 its not stalling (yet).

I have got my wife to go get me a plug but just in case does anyone have any advice?

Answer 1

If you have a coil on setup or even a coil over (both with individual coils per cylinder), change out the #2 cylinder coil with a different coil ... doesn't matter which one. If the misfire follows the coil, the coil is bad and replace. If the misfire stays at the #2, then it's something else, most likely a bad spark plug. If it's due for a tune up anyway, you'll probably want to change out the spark plugs just for common sense reasons.

Also, while not under load or under a light load like you'd experience at speed, you may not feel the misfire, but more than likely it's still there but not pronounced enough to actually be detected by you. The fact it is plain when accelerating gives me the clue it's there all the time.

EDIT:

I forgot to mention about the cat. You should see a lot of movement out of S1 O2 sensor, but only minor variation out of S2 O2 sensor. If the movement of O2 is very jagged and follows S1 movement, your cat is most likely toast. The reason is, the S2 O2 should be getting the readings of the exhaust post cat converter, which means all of the bad gasses should be cleaned up.