No spark, no 5V signals to CAS, help - Miata Forumz - Mazda Miata Chat Forums

NA (1989-1997) NA Miata discussion within. The MX5's first generation, the NA, sold over 400,000 units from 1989 to 1997.

No spark, no 5V signals to CAS, help

Old 07-04-2017, 02:49 AM
  #1  
!!!! I NEED TO POST !!!!
Thread Starter
 
Join Date: Jul 2017
Location: Rio Linda CA
Posts: 3
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.
Togno is offline  
Old 07-05-2017, 04:52 AM
  #2  
MFz Lurker
 
Join Date: May 2017
Location: Columbus, OH
Posts: 38
Default

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.
Brap-Brap is offline  
Old 07-05-2017, 09:14 PM
  #3  
!!!! I NEED TO POST !!!!
Thread Starter
 
Join Date: Jul 2017
Location: Rio Linda CA
Posts: 3
Default

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?
Togno is offline  
Old 07-06-2017, 11:28 PM
  #4  
!!!! I NEED TO POST !!!!
Thread Starter
 
Join Date: Jul 2017
Location: Rio Linda CA
Posts: 3
Default

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
Togno is offline  
Old 07-07-2017, 01:59 AM
  #5  
MFz Lurker
 
Join Date: May 2017
Location: Columbus, OH
Posts: 38
Default

Glad to hear you got it sorted.
Brap-Brap is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Kevins94NA8
NA (1989-1997)
1
10-23-2016 02:09 PM
Calane53
NA (1989-1997)
5
06-05-2014 04:36 PM
cjb3
NA (1989-1997)
15
03-18-2014 02:43 PM
Doc Toro
NB (1998-2005)
4
03-31-2013 12:52 PM
Track
NB (1998-2005)
3
10-12-2011 11:30 AM


Thread Tools
Search this Thread
Quick Reply: No spark, no 5V signals to CAS, help


Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.