P71 SuperDork
July 10, 2010 12:12 a.m.

OK, here's all the previous rants and threads condensed into one. I really need some help here, as I'm stumped. Car in question is our 93 Miata 1.6L B-Package w/ABS. It was running and driving great with a slipping clutch, so I drove it into the garage on Thursday and took the trans out.

In the midst of said disassembly, I managed to break a sensor on the back of the head. It looks like a coolant temp sensor, as it's in a water crossover line thing. It sits underneath the CAS and towards the middle of the head. I could see it clearly because I took the coil out and the CAS out in order to reach the top 2 bellhousing bolts.

Nothing else broke or replaced. Anyways, this morning I took the flywheel and had it machined. I installed the new clutch kit (stock kit since I run STS) and reinstalled the trans. After re-connecting everything I filled the trans with 2 bottles of oil (RP Synchromax).

The Miata fired up on the first try and drove over a mile of stop/start around the neighborhood to let it break in the clutch. I pulled back into the driveway to let it cool back down before trying to fine-tune the timing (I stuck the CAS back where it was so it would be close but did not hook up the timing light). The only issue was a CEL.

When I went back out the car wouldn't start. It acts like it's flooded (smells faintly of fuel and have to have the throttle wide open for it to start). After futzing around I gave up, put everything away and went to the movies. We just got back from the movies and on a whim I tried to start it.

Surprisingly it started right up! It idles steady, but the CEL is still on. The coolant temp and oil pressure gauges are both working. I drove the same 1+ mile loop with no issues, all the way to redline. As I came back into the neighborhood she stumbled a little bit (on decel) but made it to the driveway no problem. I shut it off and immediately tried to restart it, no dice.

So, ideas? Questions:

  • What is that thing I broke?
  • Is it possible I hooked something up wrong?
  • Could it be the coils?
  • Fuel Pump?

I am already missing my second points autocross tomorrow over this and I am going to have to give up thoughts of a repeat Regional Championship if I miss Sunday as well. I really, really need to fix this!

I will send a free model car to whoever ends up with the correct diagnosis!!

Thanks GRM!

EvanB Dork
July 10, 2010 12:37 a.m.

The thing you broke is probably one of the coolant sensors, there are 2, one is coolant temp and one is something else that I forget. Thats all I have to add, nothing helpful at all as usual.

fastmiata Reader
July 10, 2010 12:00 p.m.

It is a coolant sensor and the computer needs it input. The sensor merely screws into the back of the head but I am not sure if you can get one from Bubba at the autoparts store. Do you have any friends who have Miata's?

P71 SuperDork
July 10, 2010 12:56 p.m.


That stupid sensor is what caused everything. I got one at NAPA for $17, installed it, and it works perfect!

Keith SuperDork
July 11, 2010 12:06 a.m.

Glad to hear you got it. BTW, the two coolant temp sensors are for the ECU (two wires) and for the gauge (one wire). Why Mazda decided they needed separate sensors I cannot explain. On the 1999-05 Miatas, the two sensors are combined into a single piece (three wires) but are still electrically separate.

If you get a CEL with a 1990-95 Miata, you can read the codes yourself with a paperclip. Makes it a lot easier to diagnose if you know just what the car is actually complaining about.

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