Re: DIS Tach signal

["Bruce Plecan" <nacelp@bright.net>]

| This is not directly ECM relates, but sort of related I think...
| What type of output is the tach signal on a '90 Turbo Grand Prix (7727
| ECM)?
| The signal is generated by the DIS module and not the ECM.
| More specifically, is it 3 pulses per revolution?

I beleive so.

| Also, is the instrument cluster tach supposed to be dead-on accurate, or
| is it supposed to read a few RPM higher.  I ask because the service
| manual mentions a test tool in which you set its output to read 54mph
| (comes out to be 60Hz on a 4000 pulse per mile cluster), but the tach is
| supposed to read 1350rpm.  It would sound like if the test jig is
| sending out a 60Hz signal, the tach should read 1200rpm if the tach
| signal is 3 pulses per rev.  Could be the test jig sends out 2 different
| frequencies, but the fact that the speed must be set to a specific
| frequency sounds like it just sends one frequency.

Ever GM tach I've checked read fast, and some got real fast at higher rpm.
 
| Shawn Lin
| http://www2.cybercities.com/g/gmwbodycars/

I keep getting page not available
Grumpy