My S1 has developed an intermittent missfire (I thiught that at first) but when I reconnected my AFR guage it dropped very lean when the car was missing.

I checked all plugs and found no.3 to be the problem. New set of plugs and all was fine for around 160 miles from and to Ford Fair when the missfire developed as I was leaving again. I manaed to nurse the car home and again it was plug no.3.

I checked the fuel injectors and replaced the dizzy cap, leads and removed my Group A coil to make sure it was not a ignition issue.

Once again when you clean the plug all is fine.

I did a compression test and all bores except 3 came out around 100psi and no.3 was around 110psi, which I think is a little down on all.

I have plans to change the rings, h/g, cambelt, plugs and big end bearings over the next month to make it better, and until I have the head of for inspection I cant gaurentee the state of the pistons,

but does anybody have a clue?? I am a bit confused as to why it is number 3 only.