From Mexie ... to MXSE ...

[rascal]

Make sure the new cam sensor you swap in is tested on a working car first.
A mate had a similar issue and immediately thought it was cam sensor. Bought a new one and put it in, only for issue to remain.
He then spent weeks chasing the problem swapping coil packs and redoing earths etc, only to almost give up.
I asked if he had swapped the cam sensor and he said yes with a brand new one.
I swapped my cam sensor in from my running car and problem went away.

Moral of the story, don’t assume new parts are ok unless tested previously.

[Nevyn72]

So since this happened, I’ve had the (Champion) spark plugs out. I assume they are the original iridium plugs as the car has only done 63k since new. They looked fine.

Factory plugs are Denso so they've been changed at least once...

Also look for an air leak in the pipework between the MAF sensor and throttle body.

[greenMachine]

Maybe do a replace of all the pressure/vacuum lines leading to/from sensors etc? Fiddley but not ruinously expensive (I assume, never having donne it ) ... and that will take them out of the 'unknown' area.

Coils may be the problem, lots about them failing on NB8As, not so much the 8B 'cops' that I have seen. I have a spare set, LMK if you would like to try them (came out of a working 2003).

[KevGoat]

Damn I love this place! Thanks guys.

I had decided to just order most of the parts anyway as either me or someone else will need them for the car sometime in the future and it appears most of them seem to fail at some stage. Not a massive cost in the scheme of things.

When driving, my first reaction was spark plug, that's how it felt - though it was very similar to way back when one of the turbo hoses came loose (not quite as radical as that was!). But the car wouldn't even idle when that happened and now it idles fine.

Still feel it's electrical, or some solenoid sticking or something like that - but that vacuum reading keeps bugging me. Some research online seems to back up that the reading should be higher at idle, but I couldn't find anything to show if a turbo engine is different. Anyone with an SE and turbo gauge if they could see what theirs reads at idle would be appreciated.

Interesting that the plugs have been changed (thought Champion was strange!). Can't for the life of me recall ever changing them myself but no one else has worked on the car since I bought it. Can't imagine the dealer I bought it off would have gone to the expense or trouble, and it only had 39k kms on it and all Mazda services to that stage. None of my records I keep of what I do show plugs being changed. I do have a habit of renewing all serviceable items and liquids when I buy a used car so that I know where I am with it. Usually I'm pretty ocd with my records though. Bloody old age ......

Thing is, now I can't drive it, I REALLY want to drive it


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[KevGoat]

Fingers crossed but I think I've fixed it. Faulty MAF!

Woke up at 3:30am this morning and the thought came to mind I have had a spare complete NB air box sitting in my shed since I bought Mexie! I did a check online and it appears all NB8A through to 8C are the same, so thought what the heck. Swapped it in and the car started and idled nicely and it was still idling smooth once warm. Gave the throttle a few sudden blips - which always showed the problem up previously - and all smooth. Took it for a drive up our hill and the engine missed a couple of times but ran much better. Took it up the longer hill and once confident took it to redline twice and all good. Still has a couple of misses here and there, maybe clearing something somewhere or maybe this old MAF isn't spot on, so for peace of mind I think I'll just grab a new one.

Waiting for it to cool down then do a test again from cold and hope all's well.


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[bruce]

Good sleuthing Sherlock!

[greenMachine]

Same MAF for the SE?

[KevGoat]

Same MAF for the SE?

TBH I haven't found any definitive information. The question has been asked on Miata.net a couple of times but no answers. Searching parts and using "does this fit...?" all come up with the same one for all NB's and searching SE or MSM doesn't seem to show anything different.

I'm actually struggling to come up with any reason why the MAF sensor would need to be different. It's reading the intake air prior to the turbo, sending that information to the ecu, then the ecu is what would differentiate between stock, vvt or forced induction in what decisions it makes regards amount of fuel. I'm open to correction....

So anyway, still researching.....


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[Nevyn72]

Get a can of MAF cleaner before you get a new one.

If it's been in storage for a while it might just need a bit of a clean, it might even be all the old one needed...

[KevGoat]

The original one had actually been cleaned fairly recently. I'm wondering if I damaged it somehow, though I'm always careful cleaning these. Before ordering a new one, I was intending to clean both and I also want to re fit the original one back in and see if the issue comes back again. Maybe it just wasn't fitted in properly such as you mentioned about the seal (it looked and felt fine), maybe the plug wasn't connecting properly, maybe there's an issue with a wire that temporarily fixed itself with changing them over. I also didn't get chance today to have another drive to make sure the issue has properly gone away.

A few tests to do before I'm satisfied.


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[KevGoat]

Well this has been harder than I thought! Maybe my search skills are not that good, or it's just not a question that's come up much, but finding cross compatibility between the two different NB MAFs has only (for me) come up with one answer so far, from a UK club forum ...

"The FS1E is for the MK2.5 all flavours with OBD.
The FP39 is for MK2 non OBD only.
Oh forgot to say that they are not compatible."

However, nearly every advertised MAF shows just one MAF suits all 98-05 MX-5's!

Another site showed this list which would indicate the earlier FP39 is possibly interchangeable with the FS1E...

Part Number: FP39
Interchange Part Numbers:
FP39-13-15
FS1E-13-15
FP3913215
FP3913215R00
S1E13215R00

These part numbers cover various manufacturers and Models from Mazda, Suzuki and Chevy.

The FS1E is what's fitted to the SE/MSM, meaning the naturally aspirated NB8B/C models have the same MAF. According to most sale sites, this one is also backward compatible with the 98/99 model. So maybe the FS1E is backwards compatible but the earlier FP39 is not compatible with later models?

Just looked and the shed spare I had is the earlier FP39. Interesting. Some AFR tests with the FP39 would be interesting, but I don't have any way of doing that, so unless I can find more concrete information that it works, I won't be chancing anything.

Too cold and wet anyway today to do much on the car.


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[greenMachine]

If you were running an aftermarket ECU, you could do that just by plugging in the laptop and swapping the sensors, but I think you are on the stock one?

It might be worth experimenting by switching the ignition to 'on' (run), and seeing if one throws an error code when switching between them.

Best I can do!

[KevGoat]

It was idling for quite a while yesterday and had a couple k's run up the hill near us and no warning lights or code when I plugged in the OBD. Actually ran quite well apart from a couple of misfires probably caused by all the off/on/out/ins while trying to find the fault.

TBH a new (correct) one isn't much of an outlay if my original one still plays up when I try it back in, so all this is pretty irrelevant really, just my own curiosity and desire to answer a question in my own head

Still not sure about that vacuum reading.....

[KevGoat]

Swapped the original MAF back in. Car ran fine. Still some misfires and at times still felt like it was about to run rough but way better than it was. So whatever it was seems to have maybe partially cleared, but still doesn't feel completely cured. So not completely satisfied I let it idle while doing yet another check around the engine bay, and when I fiddled near the TPS the car suddenly almost stalled! It had done something similar the first time I'd been checking everything, but it hadn't done it again and I couldn't work out what could have caused it. I fiddled around some more but once again I couldn't get it to replicate. But this time I remembered I had done the TPS resistor mod way back. I wondered if maybe the two cables that had been used were shorting, so I disconnected the plug and pulled the tape off the connector wires to see if maybe there's any cable break or shorting. When I had originally removed the resistor after having the ecu tuned by Chiptorque, I obviously hadn't completely cleaned off the residual solder and one of these had become effectively a loose ring of solder - a dry joint ring - that could physically move on the cable and I think must have been causing some sort of electrical resistance or short as it connected/disconnected with the area of bare wire. I don't really understand what it would have been doing as there appears to have been no short between any wires or any sort of earth or anything, just that the piece of solder was obviously constantly connecting/disconnecting from the engine vibrations! I removed all the solder - properly this time - and cleaned the two cables and made sure they were well insulated and the car has run perfectly since! Took it for a really good shakedown drive yesterday and it felt great.

TBH I'm still not 100% sure what it all really was, or even if it is properly fixed, but a couple of things have been fixed and it's all working ... so for now I'll take the win.


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[KevGoat]

My son sent me this screenshot that's kinda cool...


Yup that's mine Both creepy what can be found out about one's self on the internet these days...and kinda cool at the same time.


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