Car running weirdly

[bruce]

Figured it out - it's a Morning car. Doesn't like getting dríven in the arvos

[Rotary]

The main thing that stands out is you say it smells of strong fumes, out the exhaust. which means fuel is getting through but no spark to fire it, then it goes out the exhaust and creates the fume smell.

A cat failure usually is a melting of the honeycomb core, mostly at the side closest to the engine, and unlikely all the way through as it will block first before melting through and your car will stop,
so its unlikely to make it louder due to its failure, and your car will be very low on power always

So my guess based on the fumes would be the coil pack. (do these fumes come always while missfiring?)

Just to confirm, when it misfires does it stall as well and dificulty restarting, or does it drive with erratic misfires here and there.

Does it Idle well or does it sound funny like running on 3 cylinders?

When misfire begins does it happen at all rev ranges, including an unstable funny idle?

That boxster tractor sound can also be if its running on 2-3 cylinders only

Still could be the fuel pump or other electrical, but if the fumes always come more when misfiring then its probably related to ignition sytem (coils)

[philz]

Yep the fumes smell when it's misfiring.

Engine idles well, no dips or fluctuations.

Does not stall by itself.

I haven't been able to drive it yet, will probably be able to drive it around the block tomorrow.

[philz]

I alright drove down the street for bit.

Misfires, exhaust smells, idle does drop at times ( but not to the point of stalling ), engine is slow to rev in idle, and there is no power anywhere while driving, very slow to pick up speed [all the obvious signs of misfiring].

Exhaust has the misfiring sound, but is not louder than norm.

From what I can think of doing, is changing coilpacks and fuel filter.

[JBT]

What a pain. Some information here on NB coil pack issues.

[manga_blue]

If the exhaust smell is sort of sickly sweet then it's burning ethylene glycol, meaning you've got coolant getting into your cylinders. Wouldn't happen to be froth or bubbles in the radiator, would there?

[philz]

What a pain. Some information here on NB coil pack issues.

JBT, in your opinion, do you believe these signs are of a failing coil pack?

If the exhaust smell is sort of sickly sweet then it's burning ethylene glycol, meaning you've got coolant getting into your cylinders. Wouldn't happen to be froth or bubbles in the radiator, would there?

Not sure, might have to check it out tommorow.
But i don't remember the exhaust smelling sweet.

[JBT]

JBT, in your opinion, do you believe these signs are of a failing coil pack?

The signs could be of a number of things philz. Coils (NB8As seem to eat them more than others) are next in the ignition trail as well as poor connections/broken wires to crank/cam angle sensors. If you could get hold of a known set of working coils off someone and swap them in it would eliminate them as the cause. Maybe an auto electrician could test them. New ones are quite expensive.

It sounds more like an electrical/ignition problem than fuel or mechanical because it's so intermittent. A bit difficult to tell though without seeing/hearing the thing.

[philz]

Cheers JBT, I appreciate your on going help.

I might even have to put some youtube vids up for the sound.

Well 9am, weather quite cold and cool.

So I start up the car, and as usual mornings... it's starts perfectly, idles, sounds everything is normal.

So I decide to have drive around a few blocks.

All I can say compared to yesterday, where I could only limp about 50ms and back, there is power everywhere.

Response is even better than before, with the new leads and plugs.

So I give a bit of squirt here and there, car is perfect, actually even made me smile with the better response and power.

So I drive for around 5mins, drive it home, let it idle, and drive around the block again.

No misfiring at any stage, car exhaust sounds a bit louder, but I'm thinking this is due to it warming up (exhaust gets louder when hot). Smells of exhaust fumes, nothing offensive- just a slight smell in the air, blows no smoke.

Also checked coolant, clean, no traces of froth or bubbling.

about 10mins later.
I start her up again, still fine, exhaust still has a slight whiff, and when revving it slightly, sounds like a mini/very soft backfire when you let off the accelerator. This is not heard when driving, and I have not heard of this sound before this incident.

edit:
After 15mins since the last start up, behold, we are back to the misfiring.

[Rotary]

As JBT said it is hard to diagnose something without being there, and even in if you where to take it somewhere, intermittent problems are hard to check for and end up being trial and error.

There's a few key things you've explained that has narrowed it down a lot.

When you say it doesn't stall but settles to a rough idle, then this rules out the the crank and cam sensors, as they will affect all 4 cylinders and will often stall the car as well.

I think JBT has had it from the first post, but as he said, with the ignition trail, its best to try, plugs first, leads second then coils or related electrical conections to coil.

So it does seem you are losing fire to only 2 cylinders whilst the other two stay working
and in NB8A one coil fires on 2 cylinders.

now it could always be the wiring to the coils, loose pin, broken connection etc but the failure once heated up points to the coils more so than anything,
(theory: the coil is made up of thin wire wire wrapped around a core, this core expands when heated and if there is a break in the thin wire, the break gets bigger as the coil gets hotter, so therefore no spark, when it cools the gap gets smaller and spark is restored, hence the intermittent problem.)

The question is if you can narrow it down to which coil pack, as when it cools it kind of goes back to normal.

A resistance test may or may not show up a fault (try it if your handy with a multimeter)

Try removing the Ignition leads 1 by 1 at the coil, and seeing if there is a constant spark jumping while car is running just after it starts missing.
(this test worked on mine as the metal bracket(earthed) is close enough to the coil mouth, Should be the same on yours, but my coils where changed before i bought the car, so not sure if anything was altered)


Try that first and hopefully it shows up with that test
(note: you shouldn't get zapped using New Leads, but move your hand away from the area, it will just jump from the coil to the lead if you keep it close and hand away)

[Okibi]

My car had the same symptoms, IF you keep driving it around on a dead coil pack you will kill the cat.

I replaced my coil pack AND O2 at the same time (because I had both on my other engine) and that fixed the problem.

I did the coil pack first ... then went to remove the O2 sensor, and when I did it was loose.

If it was loose it could have been creating that loud rally car/boxer engine noise or the coil pack failing and unburnt fuel hitting the exhaust may have.

Be VERY careful if buying 2nd hand coil packs.

I've thought about changing mine over to coil on plug or an aftermarket set of coils, I think a few on miata.net have done it.

Perhaps you could convince Mania to research it, I know a few NB8A owners would be keep for a better/cheaper solution.

[philz]

I'm waiting to see if Richard from mx5plus has a coilpack.

I've only done a little research on coil on plug (just want to fix the problem first), and I was flicking through hyperrev, and it had the Splitfire Direct ignition system.

However the Splitfire Direct ignition conversion kit for the mx5, is no longer avaible, they only make it for the Nissan skylines and silvias.

And again, this morning-cold... car works fine, around lunch time nice and hot weather, it's misfiring.

Not much to update, until I get another coilpack.

[JBT]

Here's hoping a coil pack from MX-5 Plus does the trick. A pity you couldn't "borrow" one to try first. Have you been able to narrow it down to which cylinders stop firing when it plays up?

[philz]

Yep, I just did a check just then.

I started the car up, but I don't remember if the engine was misfiring, in my mind I'm just assuming it is, because weather is warm, and in the afternoon.

So I take out the lead from the coilpack and the engine starts to shake, and the spark is jumping.

And I do it to all 4, and it seems to all be jumping, so all sparks work, then I realised that the engine is not misfiring, or it isn't misfiring anymore, because I pulled out the leads.

So I'll have to wait again and first remember to check make sure its misfiring first.

but what I have noticed is that the engine isn't misfiring despite the warm weather, when it usually does.

edit: So now I'm WTF, at least before the misfiring had some sort of pattern, I could never get it to stop misfiring in the afternoon or when it was hot, but it seems to work fine now

[Rotary]

Another thing you could try, that will heat the coils up is keeping the revs up high, Don't have to floor it, just drive along in 1st or second sitting at about 5000-6000 rpm, this should be where the coil would heat up the most,

This is kind of a test for the coils as well, then you could pull the leads of one by one(Re-Connect each after checking)

Hope this solves it, must be pretty annoying by now.