No spark, no 5V signals to CAS, help - Miata Forumz - Mazda Miata Chat Forums
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NA (1989-1997) NA Miata discussion within. The MX5's first generation, the NA, sold over 400,000 units from 1989 to 1997.

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Old 07-04-2017, 01:49 AM   #1  
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Location: Rio Linda CA
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Default No spark, no 5V signals to CAS, help

I have a 1990 Miata with a 1.6L and desperately could use some help.
  • The car wouldn't start after being parked. I.E it did not die while driving.
  • I have fuel, but no spark to any of the 4 plugs.
  • The coil packs test good with the ohm meter. There is no power switching (yes there is power, just not pulsing) on the low voltage side of the coils when cranking.
  • The igniter was switched out with a known good unit.
  • The CAS has a good ground and steady 12V power supply. Neither of the signal wires (the white or Y/B) have 5V and there are no voltage fluctuations when cranking the engine.
  • The cam spins and there is plenty of compression.
  • When the CAS is unpluged, neither 5V signal wire has any power. I checked both at the CAS plug and directly at the ECU.
  • The room fuse is good and primary power is present at the ECU (Pin 1A).
  • There is power at the ECU for the Purge solenoid valve (pin 2X) and the injectors (pins 2U and 2V)
  • There is power at the ECU Circuit Open relay (pin 1C) when cranking.
To sum it all up, it appears that I have all the correct power feeds and grounds to the ECU. However, the ECU is not sending the 5V signal to either of the CAS signal wires. We did have another ECU laying around (we cannot confirm that it is a known good unit) and tried it out. The second ECU had the same results (its possible, yet improbable, that it has the same issue). Has anyone run across this issue? Is it possible that another faulty component (Airflow meter, O2 sensor, TPS, etc.) would prevent the 5V CAS signal from being sent? Any help you can provide is greatly appreciated.
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Old 07-05-2017, 03:52 AM   #2  
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When you say CAS is that Cam angle or Crank Angle?

Check the wiring maybe? Could be some discontinuity in the wire that carries the 5V CAS signal. Find which pin on the ECU has that signal, then set your multi-meter for continuity check or Diode check and see if the wire is fine.

It could also be the crank angle sensor that is bad that is preventing the signal.
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Old 07-05-2017, 08:14 PM   #3  
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Quote:
Originally Posted by Brap-Brap View Post
When you say CAS is that Cam angle or Crank Angle?

Check the wiring maybe? Could be some discontinuity in the wire that carries the 5V CAS signal. Find which pin on the ECU has that signal, then set your multi-meter for continuity check or Diode check and see if the wire is fine.

It could also be the crank angle sensor that is bad that is preventing the signal.
CAS = Cam Angle Sensor.
The wiring isn't bad. Again, I confirmed lack of 5V at both ECU CAS pins. This eliminates the harness wiring after it.

Can anyone confirm that a bad Crank Angle sensor can prevent the ECU from producing both 5V CAS signals?
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Old 07-06-2017, 10:28 PM   #4  
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Quote:
Originally Posted by Togno View Post
CAS = Cam Angle Sensor.
The wiring isn't bad. Again, I confirmed lack of 5V at both ECU CAS pins. This eliminates the harness wiring after it.

Can anyone confirm that a bad Crank Angle sensor can prevent the ECU from producing both 5V CAS signals?
For the next guy with this problem, it was a bad MAF sensor
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Old 07-07-2017, 12:59 AM   #5  
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Glad to hear you got it sorted.
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