Getting stock tachometer to work with haltech ecu?

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Jeonsah
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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 am using the haltech Elite 1500... 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!
Last edited by Jeonsah on Wed May 31, 2017 1:38 pm, edited 1 time in total.
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jondee86
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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
interwebz about what you need to do to make this work...

Image

====================================================================
***IMPORTANT EDIT***
The above diagram and following notes ONLY APPLY if your aftermarket ECU has
an auxiliary ouput that switches to ground and can be configured to switch at the
correct frequency for your tacho. If your ECU only provides a 5V or 12V square wave
tacho output, then you will need to use this output to switch a transistor as explained
in the link provided by the OP at the bottom of this thread.
====================================================================

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

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

Thanks Jondee, you are the man!
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Jeonsah
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Re: Getting stock tachometer to work with haltech ecu?

Postby Jeonsah » Wed May 17, 2017 5:45 am

Just thought I would share some more information about this. I am using the setup that Jondee has listed above and the tachometer is still having some troubles revving beyond 5k rpm. I talked with Haltech and he said to try hooking up two relays to give it more kick. So if you run into this situation, try that.
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jondee86
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Re: Getting stock tachometer to work with haltech ecu?

Postby jondee86 » Wed May 17, 2017 7:37 pm

Pretty sure the flyback voltage is related to the coil resistance and the number
of turns. So, look for a coil with a lot of turns with really fine wire. And make sure
that the relay does not have any resistors or diodes in circuit, as these are usually
put there to suppress voltage spikes :)

Cheers... jondee86
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Re: Getting stock tachometer to work with haltech ecu?

Postby rocket » Fri May 19, 2017 8:15 am

I did this with a Link ECU and an aw11 tachometer. Back emf is high voltage, and if you just look at the circuit board on the tachometer, there is a resistor first thing on the pin that gives tach signal to bring the signal down to the input voltage level of the chip that comes after.

On my tach it was 30k. If you get a 7k resistor it'll be fine. Like 5 minutes with a soldering iron and it is perfect - it's not a hard circuit board to solder on either. I have some pics and a video of my tach somewhere...

Edit: I didn't document this project very well. Took dramatically more time to plan and test than do it. https://goo.gl/photos/ma1G4JB52gHK6XUG8

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jondee86
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Re: Getting stock tachometer to work with haltech ecu?

Postby jondee86 » Fri May 19, 2017 4:17 pm

Using the coil out of a relay is rarely known to fail to get the factory tacho working
with any aftermarket ECU that can switch 12V to ground at the correct frequency. If
it doesn't work it could be that there is extra resistance in the circuit somewhere
from a bad connection. This is the relay I used and it works fine on my tacho...

Image

Numbers are 90987-02010 / 156700-0060 coil resistance 72 Ohms 4-pin 12V plug-in

This must be a very common relay in old Toyotas as I have three more in my parts
box that I have pulled (I was going to say pocketed, but who does that ?) while
visiting my local junkyard. I'd try one of these before dismantling my dash... you
can try it with the moving parts still inside. Mine buzzed like a blowfly in a coke
bottle up to around 4000rpm before it couldn't keep up and went quiet :)

Getting the cover off takes a lot of patience, and extracting the moving parts needs
to be done carefully to avoid breaking the very fine wires that connect to the coil.

Cheers... jondee86
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Jeonsah
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Re: Getting stock tachometer to work with haltech ecu?

Postby Jeonsah » Mon May 22, 2017 9:06 am

So I looked around for one of these relays in my spare parts box and did not find one. I ended up using two spare EFI relays. The tachometer seemed to be stable all the way through the rpm. Then I took the car for a good drive and tried revving it again (redline from 1 - 3 gears). The tachometer needle started bouncing all over again and then my car bogged/eventually died. Looks like the alternator took a crap. Lol...

Once I get the new alternator in, I would expect the tachometer to work again.The haltech ecu said my battery voltage was around 11.2V when the car died. Also, I measured the resistance on the two EFI relays and they were 72 ohms. I also measured the resistance on the generic 5 pin relays and they're normally high 80's.

talk about wack a mole...
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Jeonsah
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Re: Getting stock tachometer to work with haltech ecu?

Postby Jeonsah » Tue May 30, 2017 6:03 am

So I finally got this issue fixed. I followed this guide (the external version on page 2) for the "tacho booster":

http://www.toymods.org.au/forums/thread ... ho-Booster

I went to the local electronics store and picked up the diode, transistor, and resistor needed. Tachometer works great now.
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Re: Getting stock tachometer to work with haltech ecu?

Postby jondee86 » Tue May 30, 2017 2:30 pm

Interesting. That setup is normally used when the ECU outputs a square wave
tacho signal. My ECU uses an AUX OUT (which is an internal transistor) to do the
switching to ground. So the Haltech is likely only geared to provide a square wave
output which is typically used for late model cars and aftermarket tachos.

Good work on getting it sorted :)

Cheers... jondee86

PS: Just realised this makes my original response wrong, as the method I outlined
will only work if the ECU in question can be configured to switch a voltage free output
to provide a tacho signal. I'll need to modify that post. DONE :)
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