93 Tach not working, any ideas?

[jebusama]

I've searched enough to know I don't have noise filter, looked to see if everything is plugged in properly. The only things I can find that aren't plugged in is a single pin male connector near the PTM and triangle 3-pin connector. it's bundled with them and I can't figure out where it goes. And also a 2-pin connector on the back of the intake manifold, but it's not the knock sensor. I've been fixing lots on this car and the tach is the last thing to button down. It's totally dead at this point. The only thing I haven't done is pull the cluster out and check behind it. I've never seen much go bad in the cluster until you mess with it. Any ideas as to what those unplugged items would be really helpful. I do have chilton and haynes manual but they really suck for index searching.

 

[Nvisabl]

Is the car running ? If it is and Tach isn't working check battery voltage and altenator output. Tach goes way before other electrical drop offline.

 

[Lofty]

Check your noise filter maybe?

 

[jebusama]

i didn't think my 93 used the noise filter for the tachometer.

 

[luv2rallye]

No filter. Tach signal comes from the solid white wire (pin 4) of the power transistor. It also goes to ECU pin 109 to turn on the fuel pump (so pump only runs when there's spark).

 

[jebusama]

so if the car is running fine it would seem the problem might be the tach itself?

 

[luv2rallye]

That or the wire to it.

 

[steve]

No filter. Tach signal comes from the solid white wire (pin 4) of the power transistor. It also goes to ECU pin 109 to turn on the fuel pump (so pump only runs when there's spark).

It's been a while since I looked at the code but what I remember that the ECU is looking at the CAS not the ignition pulses when it turns the fuel pump on and off.

 

[luv2rallye]

Ya Steve now that you mention it I think I remember someone saying it was the cps signal. I got distracted by my 1993 Mitchell's wiring diagrams showing ECU pin 109 being labeled Fuel Pump Control. Thanks for the correction.

 

[jebusama]

so the PTM could still be the problem then? What else does it operate? My water temp gauge doesn't work either, it bounces occasionally, I assumed it was a separate issue...

 

[luv2rallye]

Yes the PTM generates the tach signal so that part might be bad yet the rest of it could still fire the coils ok. Try to swap with a known good one (or try yours in another 1g).
The water temp gauge is something completely different.

 

[jebusama]

great that gives me somewhere to start, appreciate the help.