'93 Miata cranks but won't turn over! Please help!

[nicdotson]

My buddie bought a '93 Miata and drove it for two or three days and had to stop because he didn't have a tag for it yet. We replaced the steering wheel, took out the airbag, and tore the horn wires out. He went to drive it about 2 weeks later and it felt as if the alternator was going out (rough idle, just felt groggy) and quit running. Charged the battery and nothing. Charged the battery more and he accidentally stuck it in the backwards. We thought that fried the alternator and replaced it, it started and ran for about 10 seconds and back to how it was. He has replaced the camshaft position sensor, the ecu, the main fuse twice, the spark plugs, the plugs and wires, the coil pack, and the igniter. Still nothing. Hooked the horn wires back up how they were and tested the battery and alternator. They were fine and still nothing. We read that it could be the air bag module (blue box under dash) it was fine and still didn't work so we left it out. The check engine light doesn't come on when the key is in the on position so the ecu isn't getting power. It's getting fuel and it will crank but no spark and won't turn over. Its been to two different shops and they're still not sure what's wrong with it. Any help or advice would be great! Thanks!

[Demon I Am]

I would have guessed the main relay

[targetdrone]

This is where it's nice to have a friend with another Miata. Start swapping things until you find your gremlin. This is much faster and cheaper than buying parts.

[— kung fu jesus —]

Check the fuses in the engine bay. The main fuse is bolted in from below, so you have to remove 2 10mm nuts to lift the fuse block from the bracket to access THAT nut which secures the main fuse, should you need to change it. The others simply pull out.

Check/test the relays in the engine bay fuse block. (In the same block as above).

Test your coils.

If that fails, I would suspect the circuit control relay, which is attached to the firewall on a bracket behind the gauge cluster, left of the pass through for the speedo cable.

[— kung fu jesus —]

The circuit control relay is associated with the fuel injection, ignition, idle control valve, charging, and air bag systems. I just diagnosed mine yesterday after chasing similar issues. It's taken me 2 months.

It is often called the fuel pump relay. It is a 5 pole relay that is in a lot of different models.

I had a stock Miata to test parts on against mine and it was frustrating. That relay is ~$90. You can find them used for much less. Please find testing procedures before throwing more parts at it. I virtually have rebuilt my entire car before finding the real solution.

[— kung fu jesus —]

This is the relay I referred to above.



Here is where it is.

[targetdrone]

I got mine started for the first time this weekend. I bought it with a blown head gasket. I replaced the head since the old one was way out of spec. It wouldn't fire up. I keyed in on the problem right away. I have the Rod's book for the 1.6, but the 1.8 has the coils opposite order. (Thank you, Internet ) Swapped the spark plug wires and it fired right up. It took a few minutes of idling for the white smoke to clear up. Drove it around the block. I get to go to DMV after work for a 30 day moving permit so I can get it smogged and sorted out.

[radmachine]

Kung fu jesus is on to something here. It sounds like you have a simple, yet hard to find, electrical component gremlin. I chased one for a week or so that kept blowing the cluster fuse. Ended up being a chafed reverse sensor harness.