Aftermarket ECU -> Tacho Booster -> AE86 Digital Cluster conversion woes

[Stain]

I've been having some dramas with my digital cluster and getting the tacho to read correctly.

I've used the simple relay method to emulate a igniter coil (12v on side, ECU out/Tacho in on the other side) on my other car which is also running an Adaptronic and it works flawlessly with the analogue cluster.

However when I used the same trick on the car with the digital cluster it only half worked...
Under light/no load/backing off throttle the reading would jump ahead, as in, if I was revving at 2000rpm, the reading would oscillate between 2000 and 5000rpm. But under full load it would read correctly...

So I made up the more complex booster shown here:
http://www.toymods.org.au/forums/tec...ml#post1017046

In the hope it would fix the issue. After a quick test it provides a more stable signal, but the reading is now incorrect... It wont read past about 3000rpm under normal conditions and under full load the cluster drops away to 0rpm.

This is telling me that it's not the tacho booster causing the problem... and as the WARI software shows the correct RPM I'm assuming the ECU is outputting the correct values which just leaves the cluster or some kind of interference in the wiring somewhere in between.
I'm leaning towards interference as when I operate other electrical components such as indicators I get a fluctuation in the RPM reading and if I use the power windows the reading drops to 0rpm like when the engine is under full load.

To add to the confusion the digital cluster isn't factory to this wiring, I converted it (long story) using several guides and looking at all the wiring manuals I could find to create this: http://stain.id.au/digi-analog.pdf

All functions work as they should with the exception of adjustable illumination...
The dash lights dim when the headlights are turned on but it ignores input from the rheostat.
I've tried another switch to confirm it wasn't faulty.

I don't know enough about wiring to know where to start looking or what to look for. So any ideas will be much appreciated.

[Stain]

Reversed out of the driveway this afternoon and noticed I lose all tacho signal when the reverse lights come on as well.
This has only happened since changing to the more complex style of tacho booster.

[jondee86]

Where are you taking your 12V supply from ?? Have you tried
taking a dedicated supply direct from the battery post ??

Cheers... jondee86

[Ken_T]

Take the easy way out and run 4 regular diodes, a zener and a resistor?

[Stain]

That could work. But I'm getting the feeling more n more recently that there is something else going very wrong and this tacho situation is just a side effect.

Was doing more testing today...

Selecting Reverse makes me lose the RPM signal
Operating the Power Windows past their travel point (IE, pressing UP when they are already fully up, DOWN when they are already fully down) makes me lose RPM signal
Indicating causes the RPM signal to fluctuate.
Turning on the heater fan when the engine is at operating temperature causing the temp gauge to max out.
The speed chime doesn't make a sound when going over-speed, but goes crazy at car-park speeds.

The engine bay, under dash & body loom are from a JDM 'Kouki' Trueno which was originally automatic.
However Junction Block #1 (drivers foot-well) was destroyed in a crash so I'm using one from a ADM Sprinter. (Was badly oxidized, thought that was the cause but using a clean one now and still have issues)
The digital cluster came from a JDM 'Zenki' Trueno and converted with the .pdf I linked in the first post.
The engine harness is made by Kaizen to suit the Adaptronic/AE86. (Only wires I needed to connect were 12v, IGN 12v, Fuel Relay, Tacho & Thermo Relay)

I'm powering the ECU (not IGN 12v), Tacho Booster & AFR controller off the thick Black-Orange pin in the passenger foot-well Junction Block #4.

Brain is really starting to hurt now.

[dumbass]

black orange is ign 12v straight from the key
to make the most fo the kouki wiring and best power to ecu i would power the injectors and coils with that black orange
then the efi relay power adaptronic as that is how factory efi is done and its not to hard to make aussie carbyfusebox into efi

but sounds like u have a bad earth there are 2 earths one each side kick panel

find the tacho wire and cut it and join a 5 m long wire to it
and get yr friends car next to yours and connect yr tacho wire
to his tacho and see if it has same problems that way u are only
using yr tacho wire if prob is still there then problem is with adaptronic tune or wiring for adpatronic
which i doubt is problem
or get aftermakret tacho and run power and ground wires direct to battery so there is no issues and see if it still does it

or pull dash out and get the 3 screws in back of tacho
one is ign
one is gnd
and last is pulse
undo these screws afew turns and run wires from these screws to battery for perfect power and ground then retighten
then recheck to see if prob still there

[Stain]

black orange is ign 12v straight from the key
to make the most fo the kouki wiring and best power to ecu i would power the injectors and coils with that black orange

Yep, they are running thru that.

then the efi relay power adaptronic as that is how factory efi is done and its not to hard to make aussie carbyfusebox into efi

And the ECU is getting the power from the +B / +B1 wires (that come from the EFI relay). I'm using all JDM wiring so have the EFI fusebox, etc.

but sounds like u have a bad earth there are 2 earths one each side kick panel

Both Junction Boxes are connected firmly to their earth points, so that should not be the problem.
ECU earth I've put in the engine bay, and then run a thick earth line from that directly to the -neg terminal of the battery.

find the tacho wire and cut it and join a 5 m long wire to it
and get yr friends car next to yours and connect yr tacho wire
to his tacho and see if it has same problems that way u are only
using yr tacho wire if prob is still there then problem is with adaptronic tune or wiring for adpatronic
which i doubt is problem
or get aftermakret tacho and run power and ground wires direct to battery so there is no issues and see if it still does it

Don't have another car handy to try this one. And wouldn't an aftermarket tacho be designed to take the signal directly from ECU without the need for the booster?

or pull dash out and get the 3 screws in back of tacho
one is ign
one is gnd
and last is pulse
undo these screws afew turns and run wires from these screws to battery for perfect power and ground then retighten
then recheck to see if prob still there

If I do this, giving the tacho a clean power/earth/signal and the problem is still there? Would that point to the ECU being faulty?

[dumbass]

ok cool sounds like yr wiring is fine for ecu

can u find an aftermarket tacho to atleast try tacho rpm wire without booster
or even with booster
u need to see if its tacho problem or ecu prob ive seen them have ignition miss issues
but normally fixed by upgrading firmware
but u would notice that and i havnt heard them having tacho driver issues
how many coils do u have
im guessing 4 so maybe try running tacho of the neg on one of the coils so it bypasses ecu
it will read 1/4 the rpm but then u can put it in reverse and also push power windows up and
see if problem is still there
tacho will only goto 1500 rpm at most maybe but just use it as a guide
just simple things to test which cost nothig

giving tacho new power and gnd should hopefully fix yr drop out when u selct rev or press power window button
but it might still be in ecu so try bypass ecu by running signal from coil

[Stain]

Its running the very latest firmware (v10) and yes have a 4x coil-over-plug setup.
I will fiddle with running new tacho signal wires and see how it works/is effected.

[jondee86]

but sounds like u have a bad earth there are 2 earths one each side kick panel

Sure sounds like you are back feeding voltage thru the earth side. Have you checked
to see if you are getting a voltage differential between the J/B earth and the battery
negative terminal when you up the windows ??

Cheers... jondee86

[_FNQ_rolla_]

I agree with “ jondee86” I would be checking the back feed through the earth side(s). Because you said you are getting a lot of (electrical) interference to your tacho whenever you power anything up.
I do not think it would be your ECU.

Things I would be looking at are the;
Earth(s) to the dash
Positive feed to the dash (could be the wrong positive feed)

All the best