Getting stock tachometer to work with haltech ecu?

User avatar
Jeonsah
Club4AG Expert
Posts: 380
Joined: Wed Jan 09, 2013 10:44 pm

Getting stock tachometer to work with haltech ecu?

Postby Jeonsah » Tue Apr 11, 2017 6:26 am

Hey everyone,

Have any of you gotten your stock tachometer working correctly with a haltech ecu? I did some research on it and have not found too much about it. It appears that some people have tried using the MSD 8910 adapter but have not directly said whether it worked or not. If you got yours working, it would be greatly appreciated if you could say what you did..

Thank you!
WTB Best Motoring International VHS Volume 42!

Disable adblock

This site is supported by ads and donations.
If you see this text you are blocking our ads.
Please consider a Donation to support the site.


User avatar
jondee86
Moderator
Posts: 1948
Joined: Fri Jan 11, 2013 10:21 pm
Location: Wellington, New Zealand

Re: Getting stock AE86 tachometer to work with haltech ecu?

Postby jondee86 » Tue Apr 11, 2017 5:59 pm

Gonna post this up because there is a whole lot of confusion and plain BS on the
interwbz about what you need to do to make this work...

Image

This diagram plus a small relay and some basic wiring will get your old school AE86
tacho working using the tacho drive output on just about any aftermarket ECU. You
don't need some expensive store bought tacho converter, diodes, transistors, resistors
or some guy telling you that you need to buy an aftermarket tacho with shift light :)

The AE86 tacho in factory form is driven by a back emf spike generated by the
ignition coil and routed thru the igniter. A wire runs from the igniter to the tacho
via the big square(ish) plug on the firewall. You need to be able to locate and connect
your new tacho signal to that wire.

Dig into your spares box (or find one off a wreck) for a small plug-in relay. Doesn't
have to be Toyota one unless you are a purist. I used an A/C relay out of a spare
under hood fuse box I had laying around. Carefully prise the cover off the relay and
remove or otherwise disable the moving parts. A zip tie to hold the contacts closed
or something jammed in to keep them open will do... its only to stop the relay from
buzzing when it is powered up.

You are only going to use the coil inside the relay, not the contacts, so work out
which are the two pins for the coil (85 and 86). Use a female spade connector and
some wire to hook one side of the coil to a source of 12V switched power (only comes
live when the ignition switch is ON).

The other side of the coil gets two wires crimped into a single female spade connector.
One wire hooks up to the orginal tacho feed wire that you found earlier, and the other
hooks up to the tacho output on your aftermarket ECU. That's it for the installation.
Ziptie the relay out of the way somewhere and tidy up your wiring.

The job of the ECU is to pull 12V to ground so that the relay coil generates a back emf
spike for the tacho. There will usually be some options in the ECU software that will
allow you to select the correct duty cycle so that your tacho indicates correctly. If you
get a reading of (say) half what it should be, you need to change the setting.

This setup works... I've had it running in my car for a couple of years, and the whole
thing cost me zip as I had the relay in my parts box. If you need to buy a relay, you
can get one from any auto parts store for a couple of bucks (4-pin 10A 12V plug-in).

Cheers... jondee86
Give a person a fish, they eat for a day. Suggest they search before posting, and they learn a skill for a lifetime.

User avatar
Jeonsah
Club4AG Expert
Posts: 380
Joined: Wed Jan 09, 2013 10:44 pm

Re: Getting stock tachometer to work with haltech ecu?

Postby Jeonsah » Wed Apr 12, 2017 6:59 am

Thanks Jondee, you are the man!
WTB Best Motoring International VHS Volume 42!

Disable adblock

This site is supported by ads and donations.
If you see this text you are blocking our ads.
Please consider a Donation to support the site.



Return to “TECH: 4A-GE ENGINE”

Who is online

Users browsing this forum: samg1988 and 3 guests