Zetec popping & sneezing

[Kevp]

Iv a silver top Zetec in a kitcar. Running Jenvey throttle bodies & KMS ECU.

Went for a run out 2 weekends ago & the car was great. Turned up at Gurston on Saturday for our 1st event of the year & the engine misfires like anything.

The problem is constant. From Idle to full revs. It seriously effected our runs.

I checked the plugs & no 4 was white & clean. Others where as Id expect (blackish).

Back at base I fitted a new set of plugs & leads. Instantly better - but still the occasional pop & sneeze. Went for a short run. The problem only occurred while under a trailing throttle & at low (no load) revs.

I then took the new plugs out. No 4 is like new. The others look like they are doing the work, however no 1 is a touch cleaner. I have swapped the injectors around before the run, just in case its an injector fault.

The problem is Im at Wiscombe on Saturday & Sunday so need to sort quickly.

My thoughts are, Coil Pack? or perhaps valve related.

Help gratefully received. cheers

[fatjon]

1 and 4 share a coil in the coil pack so I think that's a biggish clue. If it runs a wideband EGO and 2 cylinders are pusing unburnt mixture down the exhaust that would make things even worse. Coil pack would be my first item on the list.