I don't have a 3rd gen Camaro/Firebird but I've used many 3rd gen parts in my project car so I hope posting here is OK

I installed a 3100 V6 in my Opel Kadett and all is working great except for a few minor issues. The engine is a late 90's 3100 converted to rear drive with a 7727 ECU, Camaro T-5 an Ford 7.5 rear axle.. Next project is to graft a tach into the existing speedo cluster. I bought several tachs from the pick-a-part: 88 Firebird V6 (Denso), 88 Toyota 4runner V6 and an 82 Datsun 280ZX. I'm hoping 1 of 3 is working but so far either all are dead or will not work with the tach signal output from the 3100 ign control module (white wire). I did measure the signal from the ICM and it is a steady 2.5V AC at idle and increases according to engine RPM as it should.

Any ideas how I can get one of these tachs to work with the ICM tach signal or is there any wire that I can tap into to provide a tach signal? I actually tried 2 different 88-92 Firebird V6 tachs assuming since they were also GM and from the same year range they would be likely compatible but no such luck.

 

I did check the 2 Firebird V6 tachs with a battery charger and both appear to working correctly - showed 2400RPM when connected to charger.

 

It sounds like the 3100 engine has a DIS ignition setup. Many of them output a 0 - 5 V square wave for a tach signal. Which is actually verified by the 2.5 V signal you are seeing on the tach wire from the ICM.

Odds are you need to convert that signal (level shift) to a 0 - 12 V signal. I know this to be true with the 3rd gen tachs. Easy to do with a transistor and a couple of resistors.

RBob.

 

Thanks Bob. I'll see what I can find on google for up converting the tach signal to 0-12V but if you have a link that would be great.

Is the EST signal from the ICM to the ECM a 0-12V pulse? After looking at wiring diagrams today, I was thinking about trying a jumper wire off the other white (ECM pin C3) or tan/blk (ECM C9) to see if either of those would provide the correct 0-12V pulse signal.

 

https://www.thirdgen.org/forums/v6/5...ml#post4419622

The EST signal is 0 - 5 V.

RBob.

 

Bummer- hoping that might be a workaround. I built a converter from an old relay using the instructions in the link below but it did not make a difference on the tach. The converter did increase the measured AC voltage from 2.5V at idle to approx 8.5V at idle and increased as engine RPM increased. Based on the measured AC voltage, it seems the converter is increasing the pulsed DC signal but still not the correct signal for the tach.



http://www.toymods.org.au/forums/thr...-Tacho-Booster

 

That design is only required when the tach requires an inductive voltage spike. The later 3rd gens don't need it. Just a 12 V square wave is required.

RBob,

 

Thanks Bob. Work puled me away for a few days but now need to get back at it.

I copied your adapter instructions from the link but have a few questions-
For the level shifter (tach), use a transistor such as a PN2222

Then:

Emitter to ground
DIS Tach out to a 10K, other end of 10K to PN2222 base (1/4W is fine)
+12 V IGN switched to a 1K (1/2W is best), other end to the PN2222 collector

The PN2222 collector to the tach signal into the car (this is the point with the 1K and collector tied together)

This circuit will invert the tach pulses, but also shift them from 0 - 5 volts, to 0 - 12 volt pulses (or vehicle voltage).



1. How critical is the specific transistor? Will an NTE159 (equivalent GE-82, SK3466, ECG159)

2. Can I make the connections and separate the transistor leads/connections with shrinktube then encase all of it in larger shrinktube? Based on my understanding of the layout, the finished product will be quite small so could be placed behind instrument cluster.

3. Since the Firebird tach does not have a potentiometer to adjust rpm, can one of the resistors in this adapter be used to fine tune the tach?

I really appreciate your help- looking forward to getting this done.

 

It isn't critical, but needs to be an NPN such as the NTE123AP.

Sure.

No, need to modify the tach driver board to do that.

RBob.

 

Great - thanks for the info. I'll go to the electronics supply this weekend and get the parts.

I've seen several threads showing which resistor to replace/modify on the Camaro tach board but unfortunately haven't seen same info for the Firebird tach.