Hi all - new to me NA 1.8 R-spec, lovely car and drove 300 miles back with no issues, but last couple of days have had misfire. Initially thought I’d hit the rev limiter but it was <5k revs, and 2 today both at about 4.8k revs accelerating in 2nd.
Gather I should replace HT leads as the first try, but I understand them to be new anyway, so it’s not likely to be that - suggestions? Does seem to be constantly at around that rev range/ All suggestions welcome - and does driving it have to wait until fully sorted or is it ok to use and keep trying to diagnose?
Apologies if this is a stupid question but are they standard mx5 7mm leads (some go to 8.5 magnacor which s’be fine too) and are they all seated properly. Also when were the plugs changed and to what? Mx5 parts sell NGK BKR6E-11 which I think are oem and that’s what’s in mine.
But past owners may have experimented with something different and like all experiments sometimes they may not work. I’m convinced a past owner took mine to a baboon troop to be fixed for a spell.
I’d check the timing lines up as well as that’s easy to check and, they sometimes get a vacuum leak. Are there any recent bills for work round the induction and injectors that may have left a leak. I’m assuming your just on a stock and clean airbox which s’be fine . While I’m guessing does the oxygen sensor look okay? I replaced mine as the wires were foxed when I got it.
Presumably the dials read normal when it’s hot and all the fluids are where they should be and all look healthy.
I suppose if it’s (say) been driven gently for a while and then getting 300mile runs and hard acceleration (which you should absolutely be able to do) your going to flush out any weaknesses that may have lain buried.
Coil pack could be involved.
Feels a bit “leccy” to me.
If it does it less or not at all while still on ecu auto enrich from cold, especially so.
Check injector looms especially No 1 pot for sheath failure.
I think your car has a diagnostic plug? My '93 has.
Might be best to see if you can use that before chasing faults with a wallet!
Cheap enough to do plugs and quality leads, that’s where I’d start.
Fuel consumption is also a good indicator to the general health of the engine and whether a sensor is out.
If pulling the sparkplugs, check if any are oil fouled (leaking cam cover gasket). When removing plug leads, if you can, take a look at the coil pack for any green corrosion. Some aftermarket leads can arc. Check and tighten intake pipes. Squirt a bit of brake cleaner at the injectors, and see if any are leaking (bubbles).
/thanks folks.
Engine was rebuilt 2.5k miles ago by reputable MX5 guy, and car is so new to me that I’m still in assumption mode - will check these things but assume many of them should be ok. I’d expect new plugs and ht leads then, but coil pack seems a possibility. It does have diagnostic port and I have an led coming on Tue…
These days to the extent I give anything to a specialist I break the jobs down into such small parcels, even I can see if it’s a good job or not. I won’t even let a powder coater blast first - I have someone who blasts and someone else who powder coats once I’m satisfied with the blasted component.
Yours cyclically and with deep mistrust.
There are doubtless great specialists out there - somewhere - although a lot have retired.
so I took off the connections to the coil pack, both the 4 pin ones and the HT leads. HT leads seem fine, but the connections at the 4 min end have some issues. One plug is missing it’s clip so it doesn’t snap into place, and the socket on the coil pack for the other is slightly broken (instead of a border all around the pins, it’s missing part of it on one side.
Any suggestions on how to replace the plug connector tor for the broken one, and whether the coil socket needs to be complete or whether that’s more minor (my feeling)?
Coil end may let in moisture is the only issue really but I would maybe look for a second hand connector as it should snap lock when you connect it to stop it vibrating loose.
Failing that a botch would be to cable tie it together if you don’t want the hassle of changing it.
thanks - think I’m going to change the loom. Ok when pushed in but does get looser over time…
