Multiple coil pack failure

Technical Area Engine, Transmission, Exhaust etc
2

Hi everyone, first post here and it’s going to be a bit of an epic. I have myself a 2000 1.8 MX5 that I bought as a non runner due to being off the road for a year or so and suffering from multiple coil pack failures. I changed the coil and it still wouldn’t start however turns over freely. 

Since then, I have replaced the fuel pump, crank and cam sensor, HT leads, spark plugs and tried a different battery.

Now, the car will start on 3 cylinders when 1 spark plug is removed and there is nothing blocking the spark plug hole however when the 4th one is back in it’s back to turning over but not starting, this is true with any combination of 3 plugs in, 1 out. I have been told that the catalytic converter could be blocked? Never heard of this myself but I assume multiple coil failures Will have damaged the cat. Can’t really get it moving as the brakes are not up to much after being off the road for so long and I don’t want to spend the money rebuilding them before I even know if it’s a runner. 

Sorry for the structure, any help would be greatly appreciated, my limited knowledge can’t carry me any further and I’m running out of patience. Hopefully looking forward to enjoying this car.

Many thanks.

Archie.

3

Hi Archie

Coil unit failure, if progressive rather than immediate will initially cause misfiring. Misfiring will mean that neat fuel is not being burnt off in the cylinders where no ignition takes place and is expelled into the exhaust and inevitably onto the cat. The heat of the cat will ignite the neat fuel, superheating the cat core and melting it and/or causing it to break apart.

I would check engine cylinder compression to begin with to make sure no serious issue with the engine. Assuming engine basically sound, I think your theory re partially blocked cat is a good one and certainly worth investigating.