Toyota Tach (VAST type factory ignition)

[dcg9381]

Does anyone know the specific signal that the factory 22RE, 22RTE, and 4AGE VAST tach takes? Mid to late 80s MR2 and Toyota pickup?
I've gone to non-VAST ignition, which I know is going to make the tach non-functional. Motor is already out, so I can't probe the factory signal.

What I know about it:
1) People using aftermarket EFI often use an MSD 8910 adapter. I have no idea what this actually does: http://www.msdignition.com/product.aspx?id=4709
2) On the truck and 4runner, people are having luck with what appears to be a pull-up resistor soldered in the tach itself, IE:

Tach-fix-resistor-installed.jpg

[litneon]

So, got the tach working.

You have to wire a 10K resister in parallel with the first 34K resister in the trigger or signal circuit. This will be different for the two different generations of pickup, but here's the pic for the 89-95 tach cluster...



I forgot to take pics, so am borrowing ones from a thread in YotaTech posted by user Tragic Drive.

Here is a pic of the earlier tach board...



You have to reduce the impedance of the trigger input circuit to accept the 12v square wave tach signal from the MegaSquirt ECU.

So an aftermarket tach adapter isn't required. Yay!

[knightrous]

I just made a tach booster when I converted my ignition system that used VAST.

http://www.toymods.org.au/forums/showth ... ost1017046

[elturbonitroso]

The relay coil method it's the one that work on the tach of old toyotas

[dcg9381]

I just made a tach booster when I converted my ignition system that used VAST.

http://www.toymods.org.au/forums/showth ... ost1017046

I'm surprised that the relay is fast enough. How's the longevity?

[slow_hemi6]

It's just the coil harvested from a common source, that being a relay. All the switching armature gets removed.

[dcg9381]

ahh.. got it!