Prolapsed ignition lead... cause of my intermittent misfire?

  1. My model of MX-5 is: Mk2 1.8
  2. I’m based near: Woking
  3. I’m looking for technical help or recommendations on: A misfire and condition of my HT leads

One week into Mk2 ownership and loving it, even if the car does have the odd issue. It’s not my daily so I want to use each issue as a learning experience.

Today (after a lot of rain) the car developed a misfire. I could tell because the engine noise changed and the car was rumbling a lot.

I turned it off and took a look at the leads, there is a small amount of oil on the bottom of each but nothing drastic. Is that much of a problem? Additionally, one of them however appears to have… prolapsed? I’ve included a pic below. What’s that all about?

After this quick inspection I fired her up and while the misfire was present for 10 seconds or so, all four cylinders then started running again as normal.

I’d really appreciate your thoughts on the below please:

  1. Is it normal to have a little oil on the bottom of the leads?
  2. Have you ever seen a prolapsed HT lead before? What could have caused it?
  3. Could the prolapsed HT lead be the source of my intermittent misfire?
  4. Should I replace the dodgy lead or perhaps all of them?
  5. Anything else I should investigate to diagnose further?

Thanks a million for your support, really look forward to contributing to this community.

You could have a leaky cam cover gasket. Take each lead out and shine a torch down the plug holes. You may have oil on the plugs too if you take them out to inspect.

A minimum, change the plug leads, plugs too and as said check for gasket leaks.


Cheers Mick will do, I’ll get the leads and plugs ordered now. Any tips on how to check for gasket leaks? I am a mechanical novice.

I took this pic of a coil pack plug too because it looked a bit moist. Any concern there?

Tell tale of oil leaks of course is the sight of oil dripping down the engine block, easy enough to spot. As I mentioned, down the plug holes too, if that’s happening it’s new gasket time, not a massive job if you can use a spanner.


I’ve heard of a number of things prolapsing but not an HT lead; accurate description though from the look of it:-)
Mick is right, the cam cover gasket has let go with oil outside the engine and also in the plug wells. The prolapse is nothing to worry about, just the rubber part at the end of the HT lead reacting with the oil. If you clean all the oil off, perhaps wash with petrol and dry out there is a chance that it will recover to some extent.
I would advise you to spend the extra money it will cost to replace the gasket with an original Mazda part.


Quick update, changed the spark plugs and they were wet with oil. Misfire came back soon aferwards. Got the Mazda OEM gasket in hand, attempting fix this weekend :slight_smile:

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If the oil on plugs looks the same colour as the oil on the end of the dipstick it’ll be cam cover gasket failure. It’s filling up in the plug wells and when the plugs get taken out they’ll appear wet with oil. Misfires can happen if enough oil gets around the plug lead caps.

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The saga continues… Successfully swapped the rocker cover gasket on Sunday and changed sparks too. used a torque wrench to make sure everything was upto spec.

Everything has been running fine until just now when the misfire came back :persevere:

What would you suggest I investigate next?

Advice greatly appreciated.

Use the diagnostics to see if there is an error code.
If not it really comes down to coilpack, leads and plugs again.
I hope the new gasket has dealt with the oil issue?

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For me, with my daughters Fiesta, it was changing the lambda sensor that provided a permanent cure

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Yes seems like gasket issue has sorted oil issue so it was a job worth doing anyway :slight_smile: thanks I will look into reading diagnostics on this car.

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Thanks, someone told me it could be a coolant temp sensor so I’m gonna try swapping that next.

As @MickAP and @rhino666 mentioned, not sure if you have changed the HT leads yet, this might be a good next step too.

Well if the leads are swapped, new plugs and the gasket sorted it could point to the coil packs. I bought a spare when I owned a Mk2 just as I’d heard they can fail and also give intermittent problems. Seems like when it gets to operating temp or after a short while you get this kind of problem, it does point to coil pack problems.
Sorry I sold on the spare coil pack or you would have been welcome to it to try, if I remember there’s two, not sure?

As I alluded to earlier, my daughters Fiesta had a similar misfire that could be fixed by replacing plugs and coil packs but only temporarily.
Replacing the lambda senor as well was necessary for a permanent cure.

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yes new HT leads on there as well as plugs :slight_smile:

Mk2 1.8 coilpacks are really cheap to buy and worth having a spare anyway.
There are two identical coil units that use the wasted spark system to energise cylinders 1+4 & 2+3. Most coilpack issues occur when the car is hot and the coil windings are expanded, exposing weakness.
Easy just to swap a known good pack over. no need to mount for test purposes, just connect HT leads & low tension plugs and rest on a piece of soft material on top of the cam cover.


That’s great advice thank you, I’ll look into getting a new or certified used coilpack. My misfire has mainly occurred when the car is cold but also happened a couple times when restarting the car after a significant drive and stopping at a petrol station. Perhaps I have had two issues all along? Coils and valve gasket causing two different misfires.

Thanks I will keep Lambda sensor on the list of potential fixes then! Great to be connected with people who have been through similar issues.

Sorry, Muzzled, I had the impression this was a hot running issue.
If the misfire starts from cold and does not get progressively worse on warming up, highly unlikely to be coilpack.