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Just had a thought. When I was logging at an autoX event a couple of weeks ago, one of the values I picked was "speed" in reviewing the logs speed showed as 0. I know I am slow, but not that slow. Where are the readings for speed picked up? My speedometer was not working that night. The last time it was because the cable had come out of the back of the guage in the dash. The other things I was logging for were A/F Ratio, timing, and RPM's. They all worked fine.
Any ideas?
Thanks

the R31 ECUs use a digital speedo. the pulses from the speed sensor in the transmission go to the speedo cluster which have some circuitry which then send a differenet signal to the ecu

The Z31 ecus probably still have the same circuitry in the cluster but convert the cable speedo signal in the cluster perhaps? If the cluster isn't working then the ecu prob wont get its signal in this case

Matt, do you happen to know where the R31 guys typically tap into this signal.

I will research this in their forums more but didnt see it right away.

R31 guys dont normally tap into that signal which is why you wouldn't find anything

Attached is the pinouts for our ECU same as the Z31. If that helps

Great, thanks Matt. That will come in handy.

the wire from the speedo unit goes into an integrated circuit in the speedo unit and then goes out through another wire into the 'speed sensor' wire on this diagram

the speed sensor signal is certain amount of pulses per second for speed

After trying my 84 na with a digital dash and getting the same results as my 84 na with an analog dash, I got 0mph for speed in the log, I went to the FSM. It appears that the NA version with a digital dash has a speed sensor that accepts the feed from the transmision via cable which is changed to a pulse and feed to the digital dash. The analog dash has the speed sensosr in the dash cluster so the speedometer cable runs to the dash. In both cases there is no feed back to the ECU. Since they don't have a speed limiter in the NA's they didn't send a signal to the ECU. This may not be the case in the A/T version.

I am trying to figure out which wire was left out on which pin and try to rerun it to see if I can get a speed signal.

Pin #29 in the turbo runs to the vehical speed sensor. That position is left out in the NA version.

I have to pull the plug on the ECU and the insturment panel and see if there is a wire. I'll let you know what I find out.

I traced the wire and there was no wire in #29 location in the plug that plugs into the ECU. I tapped into the purple wire in plug 28I which is fed from plug 16I.
I then when out and ran a log. Still no speed on the log. Can you tell me if the NA computeres have the internals for record the speed from the sensor? The pin is in the ECU, but I don't know if it connects to anything. Thanks.

Hey Russ

Well I pulled a 1984 Z31 out on the bench with a Rev3 board/Romulator and tried out several images

The usual Speed Location (000C) is multiplied by 2 to give you KM/H

However in the early Z31 this appears not to be updating on my bench. Also checked the code and it was being compared against constant values 4 (8KM/H) and 110 (220KM/H) which may not be right

So 000C might not be available on the earlier 1984-1985 ECUs which use the 8K/1K configuration. Which means speedo output may not be available

If there is a RAM address but it is different then maybe you can find it... but I have had no luck on the bench

... below is the RAM trace window in decimal. Using AGE OUT you can see when data changes ... but it would be pretty hard (and dangerous) to find speed out whilst driving so you would need to use a drill to spin the speed sensor.... thats if the ECU even uses this line as you suspect it may not

the earlier ECUs tend to not have as many inputs and functionality as later ones (especially with < 8Kbyte of code)

As a starting point, all the FSM i have access to, and Mitchal on demand show the ecu's using pin #29 and a purple wire bring the speed sensor information to the ECU. On my 84NA there was no wire in pin #29. Also NA's have no speed sensor, but the trubo's do. What is the address for the turbo models to use the speed sensor?

I will try spinning the spedometer cable by with a drill and see if I can find an area that changes.

My other car has and 88 ECU in it, but I haven't had time to run the wire to see if it will pick up the speed. I will check that out also.

Keep you posted. Thanks.

Sent you an email with details of code disassembly

- 1984 N/A address 000C
- 1984 Turbo address 000C
- 1986 Turbo address 000C

So in theory it doesn't matter what ROM image you use.... it should pick up speed


However I ran a 1984 N/A and Turbo ROM on my 1984 N/A ECU and there was no speed sensing indication

Speed sender is used for Speed limiter, and when > 20km/h also for determining when to clean AFM

Dunno why N/A one you have doesn't have this wire

NA z31's have no wire going from the speed sensor to the ecu. only the turbos have it

Even after you run the wire to the pin in the ECU it still doesn't work. I just haven't had time to see where it goes in the ECU.