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Old 07-14-2009, 06:41 PM   #1
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Default CAS Wiring Diagram for 1999 Miata NB 1.8L

I am going to be setting up a Microtech LT10s ECU on the car this weekend but the Microtech diagram sent with the unit shows 4 wires being hooked up to the stock CAS.

All of the diagrams and pictures of the CAS that I can find show that it only has 3 wires going to it.

Can anybody shed some light on this issue. I do not have the car with me at the moment so I cannot physically look and see the wires going to the CAS, but all the stock replacement CAS and diagrams I have found look like only 3 wires.

Let me know

Aaron

Edit - By CAS I mean Crank Angle Sensor, not Cam (although I believe both are 3 wires on the diagrams I have seen)

Last edited by bompus; 07-14-2009 at 06:42 PM. Reason: Added definition of CAS
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Old 07-15-2009, 12:27 AM   #2
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I'm not familiar with Microtech (and searching their site turns up no hits for Miata / MX5 install instructions that I can find) but my guess would be that the instructions you're looking at are for a '90-'97 Miata. A link to the diagram you're referring to would help.

The NAs had a single CAS mounted at the back of the head which output two signals- one with two pulses per crank rev, the other with one pulse per crank rev. This sensor has four wires: +12, GND, and the two signal lines.

The NB crank and cam sensor (they're electrically identical) each output only one signal, and have three wires: +12, GND, and signal.


cc: your mirror post at Miata.net
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Old 07-15-2009, 02:37 AM   #3
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I'll wait to see if I hear back from Microtech. Every single diagram they sent with the unit for every different brand of CAS sensor shows 4 wires going to them from the Microtech unit. 2 Crank Inputs, GND, and +12 on every single CAS for every single diagram they have (Ford,GM,Universal,Mazda,etc). I'm guessing only one of the signals is necessary for the unit to function as it only needs to know TDC if I am thinking correctly.
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Old 07-15-2009, 08:54 AM   #4
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Yo, if you get this running on Microtech you better PM me. I have previous posts asking about anyone running a Microtech, and I wanted to do so myself. Good luck with it.
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Old 07-15-2009, 01:20 PM   #5
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Quote:
Originally Posted by thirdgen View Post
Yo, if you get this running on Microtech you better PM me. I have previous posts asking about anyone running a Microtech, and I wanted to do so myself. Good luck with it.
They have assured me that it works with all the stock sensors on the 99 MX5 without having to modify or change any of them. As far as the wiring diagram goes, it looks that way as well for everything but the CAS so far.
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Old 07-15-2009, 01:38 PM   #6
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Quote:
Originally Posted by bompus View Post
I'm guessing only one of the signals is necessary for the unit to function as it only needs to know TDC if I am thinking correctly.
Nope.

With a symmetrical crank signal (as all Miatas have) and a distributorless ignition, you need a second reference signal in order to discriminate between TDC and BDC on the crank. On the NA, this means that you'd hook up to both signal lines on the CAS. On the NB, it means you'd connect to both the crank sensor and the cam sensor.

Electrically, the NB crank & cam sensors are pretty much identical to an NA CAS- they all have open-collector outputs with external pullups. The question will be whether the Microtech software can properly decode the signals from the NB, which have a different pattern from those of the NA. This is why all the NB owners who wanted a MS had to install an NA CAS in their car until the MS2 CPU came out.

cc: your mirror post at Miata.net
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