1993 MK1 MX5 Intermittent Hesitant/Misfire issue

Have you tried reading the fault codes?

It does sound like fuel starvation, you could also check fuel pressure.

Also worth checking for air leaks between the maf and throttle body.

If it's fuel you'll experience it when it is at highest demand - high revs. You'll get similar symptoms with a clogged filter, but it wouldn't clear with revs.

I'd also be going for coil. I'll see if I have specs for 1.8 coils but a quick Google will bring up the information you need. Search for "testing mx5 coils" if you have a multimeter. It sounds like spark is breaking down at load.

For this reason, check your leads as well. Set the multimeter to resistance and check each lead is similar, but resistance gets slightly higher with length. Any which are faulty will stand out. I say this as I'm on my 3rd set in about four years. Also ensure they have positive clicks when going into the plugs and inside the coil. May sound obvious, but thinking they're on the plugs can cause exactly the fault you describe.

Another possible but unlikely reason will be water in the spark plug holes. I used to get this on mine and the spark broke down exactly how you described. 5-10 miles from home it'd splitter, I'd pull over and stick tissue down the hole and then drive on. Unlikely to happen if the engine is still in an mx5 unless you've washed the engine.

Start easy and simply first.

We had exactly the same symptoms in our 1.8 NA, in that case a new set of leads solved it. As you've done those I'd be looking at coil pack. I've got a spare I'd offer for testing but it's from a '97 and I don't think they're compatible?

Vibration wise, did it start with the new tyres? Both our mx5's do it to some extent, although having the wheels rebalanaced by someone who knew what they were doing reduced it a fair bit.

There are 3 pin variants and 4 pin variants, both for 1.8s. I think it has to do with whether the tachometer is being fed from the coil packs (early cars) or ECU (late cars) but I'm not sure where the change point was.

Appologies for the lack of reply, I'm useless!

So basically, the other day it got real bad, throughout all revs, and was cutting out, i was kind of happy in a way because that in my mind confirmed cam angle sensor, right?

So i limped it home, left it a day, tried drivingg again, awful, wouldnt rev in any gear would hesitate and cut out, parked it back up and ordered a cam angle sensor.

New cam angle sensor fitted this afternoon and took it out for a drive, drives so much better.. However.

When warmed up and revving out, Theres a spot at pretty much 5k revs in every gear, almost like its hitting limiter, but if you keep your foot in it, it sorts itself out, feels horrible doing it mind you! Again its hard to describe but its a little loss of pwoer, like a clutch slip in essence but revs drop.

Now this could be timing as i didnt adjust the timing when i put the new CAS in, i lined it up the same as the previous faulty unit. I'm going to borrow a timing gun and set that asap, i don't think thats the issue though as why would timing cause an issue ONLY at 5k revs? Or am i missing something?


Plugs and leads are new, from MX5 parts, so id hazard a guess they are more than adequete and not causing the issue.

Again MAF has been changed with one off of a known good car.

Maybe coil pack but agian i cant see it causing an issue at a specific rev range consistantly, if it was a bit more random in when it did it then maybe?

I have a little LED kit thing to read codes, it read MAF sensor so thats why i changed that, made no difference so i cleared the codes and now none are present even after a drive, so its not throwing a code whatever the issue is.


It now drives pretty much alright 90% of the time its just that hesistant spot at 5k thats throwing me off, its certainly not right but i am miffed as to why.