NA8 won't start

[S2-13BT]

Hi, I've been a lurker of the forum for awhile and yesterday picked up my first ever MX5, an NA8. My mate was driving it from Melbourne to Canberra with no A/C (was about 36 deg)!! If anyone can offer any advice I'd be grateful. The car reminds me of my 1st gen RX7 I had several years ago. It smells the same inside, is about the same size inside etc, basically feels real close and brings back good memories. Pretty stoked, despite the issue that's cropped up.

So it went fine all the way to Gundagai where we stopped to top up the fuel and get him some more cold water. After fueling it up it wont start. Cranks and cranks but doesn't start.

While we waited a while for it to cool down a bit (which didn't help), we did a little googling about cam position sensors and what not, but after waiting an hour for things to cool there is no change. Eventually ended up heading back to Canberra and getting a car trailer and bringing it home that way. Safe and sound now at home!

So, some symptoms and observations based on all my googling, but not too familiar yet with different models so all the threads I read I get a little confused about it applying to directly to this car.

It's a '95 NA8
Cranks no problem, but won't fire at all
Give it a little gas and the engine just shakes pretty bad, no throttle and it just cranks pretty smoothly
With the key turned to 'on' I get the charge light and brake light only (the top two in the little window), not sure I should get the check engine light at that point
No RPM on the tacho at all during cranking!!
I expect the battery will be dead soon, so I'll put it on a charger. It's a trooper though, I've cranked the car a lot!

I didn't have any tools with me at the time! All I could do was reseat connectors and simple stuff like that. That all seems fine.

So, I'm thinking the heat has done something bad. Was nice to see the actual engine temp was kept in check the whole time by the cooling system though.

Anyway, apologies for the long post, but I certainly appreciate any help and insight anyone can offer as I learn about the car (i'll take this as a great opportunity to learn stuff about the car I might not have before).

[StanTheMan]

Are you suggesting it almost starts?
Confirm
Does it have fuel
Does it have spark

Could be any number of things.

[93_Clubman]

As STM says above, check for air, fuel & spark.
But based on your post here are some common possibles for the NA8:
Fuel pump wiring loom in tank degraded top tank connector/s (see my blackwire post);
Fuel Inj relay degraded function (in engine bay fuse & relay box) - see manga_blue posts;
Fuel filter blocked;
ECU (water or otherwise damaged PCB);
Pipe from engine air intake cross pipe to IACV come adrift;
Cam position sensor (or CAS);
MAF connector adrift;
Timing belt broken;
Cam timing out (timing belt jumped a few cam teeth);
Coils US;
Sparkplugs US; &
Sparkplug leads US.

Other items that cause issues from time to time:
O2 sensor on header;
Coolant temp sensor US (at rear of head for ECU);
Crank position sensor;
Fuel pump relay US (under dside dash); &
MAF hotwire needs cleaning.

[S2-13BT]

Thanks fellas, plenty of things to start checking.

Are you suggesting it almost starts?

Nah, just cranks and cranks. Doesn't seem like it's going to fire at all.

[manga_blue]

Tacho not working is a significant clue. The tacho is dríven by an electric pulse from the coilpacks, which are in turn fired by a pulse from the ECU which uses the CAS (cam angle sensor) as its trigger. The CAS is spun by the exhaust cam. Your fault most likely lies along that path.

Some of the tests for these are quick and free:

1. Check the exhasust cam is turning by simply unscrewing the oil filler cap and watching the lobes turn while a friend spins the motor. If you haven't got a friend ( )then spin it for a second yourself then look again to see if the lobes are in the same position. If it's not turning then you need a new timing belt.

2. The ECUs mostly fail because they got damp. Take it out (it's in front of the passenger footwell) and check it for corrosion. It doesn't hurt to drench it with electronic circuit board cleaner and let it dry before you put it back in.

3. Otherwise the ECU may not have any power because the MAIN relay has failed. I have a post about checking that somewhere n this forum.

4. NA8 CAS's rarely fail, although 93_Clubman makes a good point about wiring. Swap yours with a mate's (see point 1.)

5. NA8 coilpacks often fail and they usually wipe out the tacho pulse with them. The best way to destroy an NA8 coilpack is to go for a long hot drive on a stinking hot summer day, then pull straight off the highway and let it idle for a minute or two. This really helps to concentrate the heat around the coilpacks, which are stupidly mounted at the hottest point of the engine at the back of the head. Turn the engine off and leave it for a few minutes to slow roast the coils. Then turn it on again and ... Voila! no start! Normally only one half of the coilpack fails at a time, rarely two unless your really fry them, so usually you get it running on 2 cylinders rather than total failure. The only real test again is to swap it with a mate's.

[93_Clubman]

Hey Phil,
Didn't think mine did, so just cranked over my 1993 NA8, & no movement from tacho needle until engine actually catches.
Re ECU PCB, remove front & rear ECU case covers to look for any blackening of PCB or components in case any dampness has dried.
'Fuel Inj' (as per NA8 fuse box label) relay is aka main relay, & aka 'EGI' relay on NB8.
Agree one of the two coils in the coilpack commonly become US on the NA6 & NB8A, but never had a problem with them on my NA8s.

[S2-13BT]

Before reading the last two posts above, I've been tinkering this arvo and have made a little progress, although still no start.

I managed to determine that there WAS NOT 12V present at pin 1B of the ECU with the ignition turned to ON. I got to this point because there wasn't any voltage at the CAS connector either... I had about 1.3V on the white/red power wire from the main relay. So I popped the top off the relay and realigned the innards, and now get 12V where it's supposed to be. However, I've determined at this point that I"m not getting any spark. Or, at least while cranking from the drivers seat I can't see any spark from a plug laying on the rocker cover... My eyes are pretty good, so pretty sure there's no spark.

With the main relay apparently working OK for the time being (I'll get a replacement as soon as I can), I now get the smell of fuel while cranking and the familiar whir and click of the fuel pump priming, so I'm happy about that.

So, could be coils! Especially as I managed to hit the exact set of circumstances that apparently kills them as detailed above! I appreciate that manga_blue.

Unfortunately I don't have any mates... That have Miatas. So will need to figure out another way to test them.

Thanks again.

[manga_blue]

Yes well, I've burnt out two NA8 coils exactly that way. I should've learnt after the first one.

[93_Clubman]

Fortunately never used to leave my NA8 idling once pulled in for stops during Cbr-Melb-Cbr runs during stinkers in late Dec & Jan - must have saved me.

[S2-13BT]

I gathered some more info, but still no start.

I managed to confirm the cam position sensor is working, I'm fairly certain. I did this by testing the voltage of the SGC and SGT wires at the ECU went from 5V to 0V and back as the engine was slowly turned. I tested the resistance in the coils too, and they both checked out (although the 1/4 coil is a bit dirty inside so the connection was difficult at first).

Still no check engine light. Can anyone with a '95 confirm if the light should come on when the key is turned to 'on'?

The coil bracket is broken and missing a bolt, so I'm going to order a replacement for that anyway and keep trucking. Not sure where to check next.

[S2-13BT]

Just to close off this thread, I replaced the coil pack and it fired right up.

Thanks for the advice.

[StanTheMan]

Nice work