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Old 08-02-2009, 09:42 AM   #21
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Wait, aren't the tachs mechanical in a 90? Something is, my friend's 90 is SO f'ing noisy from a bad tach cable or speedo.
Speedo is mechanical on all NAs. The cable plugs into the tranny in the same spot as your electronic sensor.

Tach is electronic on all Miatas. On the 1.6 it's fed from the igniter, on the early 1.8 NAs (with the four-wire coils) it's fed by the two coils in parallel, on the later NAs with three-wire coils it's driven by the ECU just like on the cars with the non-functional headlights.
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Old 08-02-2009, 09:59 AM   #22
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I don't know if this will help but for a while I was suffering major battery discharge and my Tach was not reading correctly. Nothing bad was going on mechanically and the engine was completely fine in all aspects. The most notable feature of this annoyance was the Tach movement. I would accelarate to about 4k RPM and then the tach arm would swing all the way round to 0 (going CW) and then stay there. Only after turning off the engine and accelerating to about 4k RPM (couldnt tell as the needle was at 0) when it would spring into life again and return to the reading above 4k and be fine for the rest of that trip.
It took two weeks to find the problem and I drove it everyday while it was happening to work and back. The cause was the engine earth strap near the heater core pipes. I tested it early on as part of the diagnosis and it had 0 resistance from end to end so I assume it was good as there was no visible wear either. I got pissed off basically and made my own ground kit from left over amp cabling. Fitted my own version with shiny new cable and everything was fine and has been for over a year with OEM ECU and Emerald K3.
Im not saying this is what you have but replace the wire as it might help and it costs sod all.
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Old 08-02-2009, 04:33 PM   #23
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Speedo is cable driven in an NA
well, then the fuse is as likely as a timing belt at this point, no? The tach would drop to zero, like he said. What kinda miles on are the belt?
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Old 08-06-2009, 12:49 PM   #24
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Wow, I was suppose to get email updates whenever someone replied. I got an email for the first reply but none after that. Well, today I am looking at the timing belt. When I took the oil cap off I saw everything turning but I am still gonna check it out. Another question is that I checked out my Trottle Sensor and opened it up and noticed that when I pulled the cable to get the rotation none of my switch contacts were touching at all. Could this be adding to my problems?
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Old 08-06-2009, 12:55 PM   #25
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Huh, the timing belt DOES sound like a good candidate, but... so does the fuel injection fuse? Certainly a simple one as well, slightly less likely but an easy fix. :-) It'll shut off really quick that way, and yes, no tach.

Wait, aren't the tachs mechanical in a 90? Something is, my friend's 90 is SO f'ing noisy from a bad tach cable or speedo.
What would drive a mechanical tach?
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Old 08-06-2009, 04:57 PM   #26
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What computer do you have? If its OBD-II you can get a reader, if it's MS you can read it out.

The simple answer is CHECK YOUR FUSES. If the cam is turning, everything is cool, don't waste time looking at the belt. Do you get dash lights?

For the motor to utterly die suddenly, it's almost always wiring or the belt. It's not the belt so move on.

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Originally Posted by Joe Perez View Post
Speedo is mechanical on all NAs. The cable plugs into the tranny in the same spot as your electronic sensor.
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Originally Posted by jayc72 View Post
What would drive a mechanical tach?
Need I say more?
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Old 08-07-2009, 12:23 AM   #27
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Checked out the belt and my E's and I's are way...way...off. I checked all my fuses and they were fine. I get dash lights and my radio works and they worked perfectly when the break down happened. How do I know what computer I have? I checked my fuel injection fuse and i got a great reading on it and I followed my haynes manual on the check. Any idea about my TPS?
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Old 08-07-2009, 01:06 AM   #28
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I really wouldn't worry about the TPS - why did you pull it apart anyway? It's not too hard to check, btw, read resistance from the middle pin to either of the sides, see if it changes .....

Oh, wait, what year is it?

A pic of the cam gears would be helpful, while you've got the camera out the TPS would be good too
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Old 08-07-2009, 01:40 AM   #29
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It's sounds like the throttle cable is not attached. check and see if the throttle cable came off of the throttle body. I've had 2 come loose on customer cars.
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Old 08-07-2009, 01:48 AM   #30
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What would drive a mechanical tach?
Check out late 60s Vettes for the answer. I knew someone that had a nice '68 with an LS6. Went for a ride in it, great car.

A mechanical tach is no different than a speedometer, works the same way, just measures a different shaft speed.
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Old 08-07-2009, 02:21 AM   #31
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I've had a few bikes with them, and an old jeep. Typically taken off the cams to keep the wire speed down, btw. Nonetheless, it's a gear on something which rotates.

What's really slick is speedos which are just extra numbers painted on the tach for each gear. :-)
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Old 08-07-2009, 04:29 PM   #32
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What's really slick is speedos which are just extra numbers painted on the tach for each gear. :-)
Thats sick! What vehicle was equipped with that OEM??
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Old 08-07-2009, 06:54 PM   #33
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Honda! Um, some 125 dirt bike. :-)

Sigh, I can't find it after like a half hour of looking. Some 125 version of a 250 honda dual-sport I took my MSF course on.


At least that looks cool.
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