So I ran into a missfire issue recently with my 4age smallport ke70. Just last week I put 98 octane into it for the first time as the previous owner was using 91. The car sat until a few days later where I took it for a spirited drive and one final hoop down the street before pulling into the driveway which is where I then noticed the idle had dropped off 100-200rpm and minor a missfire had surfaced. I just automatically assumed perhaps the ecu was still coming to terms with a now higher octane fuel.

regardless today I went and got new plugs which were identical to the ones currently in the car, in which I discovered the old plugs were quiet black (I did suspect the car was on the rich side). I installed the new plugs where I then turned it over to which it did, but was quite rough and sounded to be missing once again but with also black/grey smoke coming from the tailpipe and exhaust manifold which I didn?t realise was leaking.

I turned the car off and pulled the new plugs out, sure enough black as the ace of spades. Perhaps I?m over analysing the previous few days but what you guys suggest investigating going forward? I would suspect an ignition/spark problem perhaps checking the resistance of the leads, dizzy and also a compression check.

thanks guys