AE71 Tacho mod for modern ignition.

[LittleRedSpirit]

Hi everyone. If you are like me, and you run coil on plug ignition or coilpacks, you probably have connected the tacho wire and noticed that the tacho doesnt function. Mine would do the odd jump and show different data if you turned the lights on or went into reverse, etc. It never actually worked in the 3 years Ive had a 20v ae71 on the road.

I decided yesterday enough was enough so I found the info for the GZE tacho mod into ae86. I then did a few experiments with my tacho to get it working as it should.

The ae71 has a different Tacho circuit board to any other corolla. It has a variable resistor from standard to adjust the tacho readout which is something that nobody has noticed on other corollas from what I can tell. Its quite cool really.

The process for adapting your tacho so it will function correctly is quite simple and outlined in the below before and after photos.

You will need one 15kohm resistor and and capacitor. If you want a greater range of adjustment you can go to a variable resistor with a greater range of adjustment.

Before:
15911

After:
15910

[Philbo]

Wow, that's cool man, gonna do this to mine for sure!

[LittleRedSpirit]

Yes a couple of others have done this and reported it worked great for them to, so go for it eh. Its great to have a little data.

[trikzlane]

thanks heaps matt, great article

[JrMr2]

Could it work for a Mr2 tacho??

[b1gb3n]

would this work for adm ae86 as well?

[DR86FT]

any info for the digi dash?

[LittleRedSpirit]

Nope, never played with one. Not to say it cant be done, but I would need to look at one and fuck with it, Might be unsuccessful. Just open it up and if it has a similar circuit board to the analogue ones then you could possibly work it out.

[JDMWheels]

Very Cool Matt!

Wish i was a little bit more proficient on the electrical side of things.. will keep this bookmarked for when my motor goes in.

[LittleRedSpirit]

Haha, Im not doing this according to electrical theory. I did my mod based on the ae86 mod info that I found. I related it to the circuitry architecture in the 71 tacho, and worked out what to do by comparing them and the resistor values. I followed and described the circuits and saw how they differed, then was able to select a few values based on the ae86 mod, and it worked. Not rocket science, and from an electrical theory point of view, I cant explain myself, but there really is no substitute for just giving stuff a go. Considering how simple it really is, its kinda shame on all the electrical genius types that assured me its possible and failed at it without ever having actually worked out how to do it. I cannot see why a decent auto wiring guru would let a car leave his sight with this unfinished.

[johnblz]

hey matt,
Will this work with a ke70 tacho dash? I ripped it out and it looks like this, a bit diff to your pics.
Also for the signal, do i use the wire from the ecu?
ive got a ca18det in my corolla. thanks man.

http://www.ae86drivingclub.com.au/dcimages/1/5/9/5/6/399709.jpg

[dove grey 64]

Haha, Im not doing this according to electrical theory. I did my mod based on the ae86 mod info that I found. I related it to the circuitry architecture in the 71 tacho, and worked out what to do by comparing them and the resistor values. I followed and described the circuits and saw how they differed, then was able to select a few values based on the ae86 mod, and it worked. Not rocket science, and from an electrical theory point of view, I cant explain myself, but there really is no substitute for just giving stuff a go. Considering how simple it really is, its kinda shame on all the electrical genius types that assured me its possible and failed at it without ever having actually worked out how to do it. I cannot see why a decent auto wiring guru would let a car leave his sight with this unfinished.

nice work matt, could imagine the satisfaction you would have felt when you fired the car up and saw that it worked

[Futo_gt86]

Digging this one up.

Firstly, thanks for the write up, and I applaud your efforts!

Got a couple of questions here.

What is the variable resistor you have used pictured 1k, 10k, or 100k ?
Also the Jaycar variable resistors have 3 terminals, where as the factory variable resistor has 2.
There is an extra hole in the board that will accept the third terminal, but not used with factory variable resistor?
Did you just solider it to this point?

Did you wire this from one -ve of the COPs to the tacho?
Or did your ECU (which I think was an Adaptronic) have tacho output wire that you have soldered in to dash cluster harness to run the factory tacho?

Can this mod work with coil packs with separate ignitors running in wasted spark?
Or, is this mod specific for coil on plug conversion set up only?
If COP only, where yours wired in batched pairs wasted or sequentially?

Any help would be much appreciated.

[LittleRedSpirit]

Digging this one up.

Firstly, thanks for the write up, and I applaud your efforts!

Got a couple of questions here.

What is the variable resistor you have used pictured 1k, 10k, or 100k ?
Also the Jaycar variable resistors have 3 terminals, where as the factory variable resistor has 2.
There is an extra hole in the board that will accept the third terminal, but not used with factory variable resistor?
Did you just solider it to this point?

Did you wire this from one -ve of the COPs to the tacho?
Or did your ECU (which I think was an Adaptronic) have tacho output wire that you have soldered in to dash cluster harness to run the factory tacho?

Can this mod work with coil packs with separate ignitors running in wasted spark?
Or, is this mod specific for coil on plug conversion set up only?
If COP only, where yours wired in batched pairs wasted or sequentially?

Any help would be much appreciated.


Its been a couple of years Ill try and remember.

I had Cops in wasted spark, but it shouldn't matter what you do if its getting the signal from the right source. I believe I used the tacho wire from the adaptronic connected to the factory tacho wire that usually goes from coil to tacho cluster, blue wire from memory on the adaptronic loom, and black wire in the car I think, at least in my scenario.

The spare wire on the cops is unused un this application as they need to be brought together and connected to the factory computer to create a tacho signal from memory in the standard application. This is redundant here.

The variable resistor value was slightly higher than the factory variable resistor. I cant remember the figures, but I believe the factory variable resistor will be adequate. If you insist on swapping it out then just test its values with a multimeter and purchase one with a more broad range of adjustment. Its great, it lets you wind the needle up and down to sync it with your ecu tacho. Cant remember what I did about the three pronged resistor, I guess I just tested and found 2 terminals that had variable resistance and installed those ones to the board. Is the hole for the third even wired in on the board?

[Futo_gt86]

Cheers for that.
Mircotech LTX8 I'm using has Blue/White wire for tacho, I'll connect to factory tacho coil wire.
I don't have COP yet, but understand IGF is disregard, and why.
I have left the factory variable resistor in place, I have a few different value variable resistors as back up, like 30c each pfft.

I'll go to PM for the rest as is not relevant to topic.
Thanks,

Ali