my 1991 SPI Cooper failed its MOT on emissions: hydrocarbons too high. The MOT tester told me it is misfiring, and he is correct.
Once the engine is warm and idling, cylinder 3 doesn't fire. But it does when the car is first started up. The other cylinders all seem to be firing OK.
I've changed distributor cap, leads, plugs, and it hasn't fixed the problem.
So that led me to think that its not the ignition electrics.
I checked the valve clearances. I've done a compression test, and all 4 cylinders give the same reading at 160PSI.
So that leads me to think that it's not the engine or cylinder head.
I've gone through the usual checks in Sprocket's super useful SPI posts. Vacuum lines look OK. I've changed the lambda sensor (didn't make any difference).
I've put a Gunson colour tune plug on cylinder number 3 to watch what happens. Ignition fine when the engine first starts up from cold, but when the engine is warm cylinder 3 stops firing. I can still see the sparks, just no explosion. So I reckon that rules out the ignition electrics.
Now I'm stumped. If the compression is the same in cylinder 3 as in 1,2 and 4, is there any way this can be caused by a problem in the cylinder head, head gasket, or engine?
Can any of the (many) SPI issues that produce misfire and bad idling lead to a systematic problem in one cylinder only?
Any advice much appreciated on which direction I should be going with this.