DirtyBirdRacing
20+ Year Contributor
- 762
- 18
- Nov 25, 2002
-
Chicago,
Illinois
These past few months on my track car I have removed about two rubbermaid containers of wiring and saved 60+ pounds on unnecessary wiring, dash, instrument cluster, etc. However I have had one issue I haven't been able to fix and I have searched everywhere I could on how to fix it and none of those fixes worked for me. Hopefully someone here can help me.
Car is a 1991 TSi AWD, running 300M COP with the 1991 PTU and running ECMLink V3 (so stock ECM/MPI relay setup). I have the Autometer 3904 Tachometer and a voltage gauge (16V system) in place of all the stock instrument cluster stuff.
I first tried hooking up the tach signal wire (pin 4 PTU, pin 109 ecu) directly to the autometer tach signal wire. This didn't work as I think that output is a 5V square wave and this tachometer wants a 12V square wave. From what I read some people use a pull up resister to do this but I couldn't find the value for the resistor needed so I went down the route of getting a MSD 8918. From what I understand a MSD 8918 and Autometer 9117 will do what I need, but the MSD 8918 doesn't require splicing (clamps around wire) and I wanted that as I couldn't find consensus on what wire to tap into.
I have tried the wire mentioned above, CAS sensor (ECU pins 21 and 22), MPI relay pin 3, ECU pin 54 and 55 (coils on PTU), and even a fuel injector wire as a last gasp, . All these hook ups were at or near the ECM.
I didn't get anything on any of these, any thoughts? The ECM engine speed reads just fine in logs.
Two interesting things I noticed:
-When I tapped my screwdriver up against the pick up on some wires the tach needle would bounce with my tapping.
-When hooked up to the MPI relay pin 3 (black-white wire) the tachometer showed 1000 RPM during cranking and when the engine transitioned to start it dropped to zero, so I think I got everything else wired up right in terms of good power and good ground.
Thanks in advance.
Car is a 1991 TSi AWD, running 300M COP with the 1991 PTU and running ECMLink V3 (so stock ECM/MPI relay setup). I have the Autometer 3904 Tachometer and a voltage gauge (16V system) in place of all the stock instrument cluster stuff.
I first tried hooking up the tach signal wire (pin 4 PTU, pin 109 ecu) directly to the autometer tach signal wire. This didn't work as I think that output is a 5V square wave and this tachometer wants a 12V square wave. From what I read some people use a pull up resister to do this but I couldn't find the value for the resistor needed so I went down the route of getting a MSD 8918. From what I understand a MSD 8918 and Autometer 9117 will do what I need, but the MSD 8918 doesn't require splicing (clamps around wire) and I wanted that as I couldn't find consensus on what wire to tap into.
I have tried the wire mentioned above, CAS sensor (ECU pins 21 and 22), MPI relay pin 3, ECU pin 54 and 55 (coils on PTU), and even a fuel injector wire as a last gasp, . All these hook ups were at or near the ECM.
I didn't get anything on any of these, any thoughts? The ECM engine speed reads just fine in logs.
Two interesting things I noticed:
-When I tapped my screwdriver up against the pick up on some wires the tach needle would bounce with my tapping.
-When hooked up to the MPI relay pin 3 (black-white wire) the tachometer showed 1000 RPM during cranking and when the engine transitioned to start it dropped to zero, so I think I got everything else wired up right in terms of good power and good ground.
Thanks in advance.