350 sbc tach signal to dash?

[Sean Foster]

Hey yall, got a 91 80 series that originally had a 3FE in it and after 5 years I’ve finally decided I want to make the factory tachometer work. My setup is a TBI350 with a Holley sniper 1 just handling fueling, ignition is a HEI big cap coil setup, I believe the factory dash gauge looks for a high voltage signal off the negative of the coil to drive the gauge but obviously that’s at 8 pulses not 6 like the gauge expects, my other problem with just pulling off that wire is how it may effect the snipers tach signal quality since that is highly dependent on a quality connection.

So then that leaves me with pulling the 12 volt square wave from the sniper unit, similar problem tho is it’s v8, so obviously a Dakota digital decoder to drop it to 6 cylinder signal but then I still have the problem of trying to supply the 12 volt square wave to the gauge while it expects the high voltage signal instead. Any ideas would be greatly appreciated, photos included so it’s not just a wall of text.

 

[NeverFinis]

I don't know if your tach has it, but if it has this POT, it can be adjusted to a V8 signal (4 pulses/rev)

See more here, about half way through this post: Build - LX450 "Rex" Build - https://forum.ih8mud.com/threads/lx450-rex-build.1254004/page-6#post-15340174

 

[Sean Foster]

I don't know if your tach has it, but if it has this POT, it can be adjusted to a V8 signal (4 pulses/rev)

View attachment 4218659

See more here, about half way through this post: Build - LX450 "Rex" Build - https://forum.ih8mud.com/threads/lx450-rex-build.1254004/page-6#post-15340174

I’ll take a peek then and hope it’s

I don't know if your tach has it, but if it has this POT, it can be adjusted to a V8 signal (4 pulses/rev)

View attachment 4218659

See more here, about half way through this post: Build - LX450 "Rex" Build - https://forum.ih8mud.com/threads/lx450-rex-build.1254004/page-6#post-15340174

i believe the 1fz tachs just use the basic square wave from the ECU, I believe the 3fe gauges pull from the igniter expecting a much higher amount of voltage like old school tachs

 

[NeverFinis]

I’ll take a peek then and hope it’s

i believe the 1fz tachs just use the basic square wave from the ECU, I believe the 3fe gauges pull from the igniter expecting a much higher amount of voltage like old school tachs

On the 1FZ-FE, signal travels from the Igniter -> Tach -> ECM.

 

[jonheld]

On an OBD1 80 (FJ and FZJ), tach is fed from the igniter.
On an OBD2 80, tach is fed directly from the ECU.