NB 1.8 missing under load. Any ideas??

[MaddoMX5]

Hi guys,
I'm a newby here, I've just jumped into the world of MX-5's (purchased my 99 NB yesterday) and I broke it today (good start)
It's missing under load, I can hear what sounds to be like a spark jumping around the coil pack and there seems to be a previous repair there. Is there a common problem that the previous repair didn't fix properly? I've taken some photo's, the wiring repair can be clearly seen but I don't know what they were bypassing/repairing, hopefully someone can steer me in the right direction, thanks in advance for any help
Cheers
Colin

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[93_Clubman]

There is a common problem with the wiring loom weakening internally where it exits the top of the coil packs. Spark plug leads & the NB8A coil packs themselves are also a common problem.

[manga_blue]

As Paul said, the wiring leading into NB8A coilpacks is prone to internal failure. It looks like this has happened to yours and someone has done a pretty rough repair on that. The miss you have now may be due to a fault in that repair or the same fault now occurring on the second coilpack plug or a failing coilpack or failing HT leads or spark plugs.

You've really got two choices: either do a step by step repair and replacement of wires / plugs / leads / sparkplugs / coilpacks on the original setup (starting with the cheapest and easiest first) or else convert the whole lot over to a Toyota COP (coil on plug) setup. It all depends on your own level of skill with auto wiring and ignition systems or on what your auto electrician is prepared to do and charge.

Edit: oh yes, welcome to the forum.

[MaddoMX5]

Thanks very much for your advice guys,
I started with spark plugs today, seemed to better until the engine warmed up.
It stutters as soon as you touch the throttle and stutters under load at lower revs until it gets to around 2500-3000 revs then takes off and revs freely.
It feels like an electrical breakdown, so I'll follow your advice and replace things step by step and see when the fault disappears.
thanks again for your advice
regards
Colin

P.S. Will extractors fitted to a 1.8 in an NA (1990) fit in my NB? (1999)
I'm looking at purchasing a second hand exhaust system and clearly it would be advantageous if it fits

[manga_blue]

You're probably on the right track. With those symptoms I'd be doing spark plugs and spark plug leads first.

Coilpack failure symptoms are usually a fair bit worse because when one coil fails it takes out two cylinders.
Coilpacks usually start to fail when they're hot, like on a long slow climb or a really hot day or left idling for a while straight after a hot run.

[Black_Penguin]

With the extractors, the NA wasn't a 1.8 until 93 and they will bolt up to the head (if 1. however they will not match the midpipe location and a complete system will need the hangers changed and possibly a few other things as well.

[93_Clubman]

Additionally, re headers, ADM NB8 OEM were quite good, so little to be gained. In contrast, USDM NB8A headers were rubbish, so good gains possible.

[hks_kansei]

Plugs first.
Then leads.

If they fix it, brilliant, if not no harm since they probably needed doing anyway.


Coil wise, i'd be first off checking that wiring, make sure all the connections are secure and insulated.
It's not the best looking wiring, my wiring looks just as sh*t, but at least I put loom tube over it to hide the problems.

[smy0003]

Plugs first.
It's not the best looking wiring, my wiring looks just as sh*t, but at least I put loom tube over it to hide the problems.

Loom tube makes everything professional

[MaddoMX5]

Thanks again everyone for your help, I'll change the leads next, check the wiring and tidy it up, we'll see what happens after that.
I'll look into the suggested headers, thanks again
Colin

[93_Clubman]

I'll look into the suggested headers

Suggested headers are the factory ones, which you've probably already got - following thread has some pics of factory US domestic market NB8A versus factory Aust domestic market NB8A, as well as factory Aust domestic market NB8B headers - if they'll fit NB8A, factory Aust domestic market NB8B headers might give some improvement, although look fairly similar to Aust domestic market NB8A: viewtopic.php?f=81&t=68978

[MaddoMX5]

Thanks 93_Clubman,
I checked out the link you supplied, Nitro Dan noted that the Australian headers pre 01 were no good (probably what I have being a 99) though when looking at photos of NB8A headers and NB8B headers, I couldn't see any notable difference (forgive my ignorance if there is) maybe they're bore sizes are different?
Maybe I should pursue headers from 01 onwards and get a new system from there back?
All advice greatly appreciated.
My 99 NB has done 215,000klms and is totally stock, from reading various forums and threads, I'm thinking of doing the following,
Coil overs and swaybars
Cold air intake
Headers and exhaust
Rings, bearings and clean up
Shave head 40 thou ( increase comp from 9.3 to 10.1)

Joining WA MX5 club and looking forward to learning how to drive it, meeting club members and getting advice on what moderately priced mods I can do to get the most out of it without blowing the budget.


BTW: New leads fitted today fixed the miss, she's purring along beautifully, however I've noticed a vibration that seems to got through the car like a "wave" every couple of seconds or so when cruising on around 70 at 2500rpm ish, it's doesn't seem to be in the steering (no shake or wobble) could be in the rear.

Again, all advice greatly appreciated.

Cheers
Colin

[StanTheMan]

Really? At 215 k km she's only just run in.
Check the pressures. If they are low or there is a big variance in compression maybe.
I wouldn't break her open unless there is good reason.
Personally I'd be inclined to spend that money on a Torsten. But each to thier own

[manga_blue]

Check for broken or collapsed rubbers inside the engine mounts.

[93_Clubman]

Dan may have had the USDM NB8A headers in mind.
Vibration issue reminds me a little of the persistent issue Wivvix had:
viewtopic.php?f=30&t=34151
viewtopic.php?f=30&t=43014&p=551537#p551537