'90 Eunos Misfire Under 2krpm? Any Help Appreciated!

[Trackpug]

It only happens when warm and off-choke and is fine above 2000rpm. It started when I was driving through heavy rain which may or may not be relevant. Any ideas?!

[MX-5 Lazza]

My first guess would be plug leads but it could also be engine temp sensor or coils...

[BonzoG]

My '96 had been suffering the same thing since the heater inlet hose ruptured last week and soaked the ignition coils and lead #4 in steam - misfire only when warm and rapidly applying wide open throttle. Completely fine when cold, or when you gradually increase the revs. Made moving off at lights fun!

I squirted a bit of WD-40 in each of the coil terminals then wiped it out with a clean rag, thoroughly dried out all the electrical connections with a hairdryer, and wiped down the contacts inside each end of the leads. With the plugs in, I stuffed a rag down each of the plug wells and wiped them down as best I could, then removed the plugs and wiped the contacts and cleaned the business end.

Has been fine ever since but your mileage may vary - I would have just swapped the plugs and leads round rather than go to any effort, but I'd only bought them the week before! If you have to drive it I'd try to avoid letting it get near to misfiring; the unburnt fuel apparently makes a mess of the cat pretty quickly.

[Rollcage]

Most often leads, MX5s seem very sensitive to quality and condition of them

[Sherpa]

My 1995 1.8l was doing this after a 250 mile trip, new plugs and leads sorted it out. The guy who did the work said the leads are prone to this because they're routed over the top of the block. Not sure if that's true but it makes sense to me.

[snotrag]

Sherpa said:

The guy who did the work said the leads are prone to this because they're routed over the top of the block. Not sure if that's true but it makes sense to me.

It is true. It will most likely be leads, and their proximity to the camcover is something that adds to it. If you have knackered leads, run the car with the bonnet open in the pitch black, and you can see the aurora/arcing through leads insulation into the camcover :-O



I've done 2 sets of leads in on mine already in 2 years. (note that my current, 'stock' type leads, the 7mm ones on 5parts, are lasting longer than the expensive 8mm posh yellow ones they sell).

[Trackpug]

Just an update, changed the leads (£26 from GSF as opposed to £76 from Halfords with a 4 day wait 'probably') it ran perfectly straight away. Thanks for responses