Jump to content
Ultimate Subaru Message Board
R4C

Were is the Tach wire ? Digi Dash " EJ Swap"

Recommended Posts

Anyone tell me what the wire color would be for a 87 turbo wagon with digital dash. Might you know if with my EJ22 swap if there is going to be any problems as far getting a true reading. Thanks All Yall !

Share this post


Link to post
Share on other sites

when i put my EJ20G into my 88 GL-10 with the digi dash, i tryed for hours to get the tach to work. i could not get it to work at all...

 

i had to get an Autometer tach adapter insted, with an exturnal tach.

Share this post


Link to post
Share on other sites

I haven't been able to get my tach to work either. Car is an 86 GL10 wagon with orange digidash. The donor Legacy was a 1990 / three-plug-style connection to the engine harness.

Share this post


Link to post
Share on other sites

i just picked up a 1986 gl-10 turbo wagon with ej22 from 97 impreza outback and the original digi-dash but, unfortunately, it as well has a tach that doesn't work.

Share this post


Link to post
Share on other sites
I believe Bram got his digi tach to work on his XT with EJ20G swap.

 

Indeed correct. Engine is a EJ20G Turbo in a 1986 XT turbo with a digidash installed.

 

From what I know, I just used the tach wire out of the ECU and connected it to the digidash tach input.

 

Best way is to check your FSM and turn to the electrical chapter where you see you complete ECU pin out. Then you'll make no mistake which wire does what.

Share this post


Link to post
Share on other sites

My '88 GL10 needed a slight mod to the green digidash to get the tach working with the EJ20G. It's expecting a high voltage (peak primary volts) from the coil primary, but the output of the ECU isn't enough to trigger it.

 

Anyway the fix is to solder a 1k resistor in parallel with resistor 112 which is a 36k resistor. This lowers the threshold voltage so it can pick up the ECU signal. Tach works perfect now.

post-9154-136027654155_thumb.jpg

  • Like 1

Share this post


Link to post
Share on other sites
Anyway the fix is to solder a 1k resistor in parallel with resistor 112 which is a 36k resistor. This lowers the threshold voltage so it can pick up the ECU signal. Tach works perfect now.

 

Nice work. Do you know if this is the same on the older orange dash? I'm about to hookup a 95 OBD-II ECU to an '85 w/digi dash. I may need to come up with a fix.

 

GD

Share this post


Link to post
Share on other sites
Nice work. Do you know if this is the same on the older orange dash? I'm about to hookup a 95 OBD-II ECU to an '85 w/digi dash. I may need to come up with a fix.

 

GD

 

I've never taken an orange one apart, but it's quite possible it uses a similar circuit. I just started to trace the circuit on mine by following the tach signal, and the resistor was the first thing I came to. :D I tried a few values to ensure that the 1k would give good margin.

 

I can help you mod yours, open it up and take a pic.

Share this post


Link to post
Share on other sites

may need a tach fillter like a gm uses ive had no trubble geting tach to work on ej covertions ej haress black with blue stripe ea harness yellow of coil leads mind you we have verry few digital dashes but it all works the same i belive if i remember right the digital dash was not so good whould replace it with loyale dash that has all 4 gauges and analog

Share this post


Link to post
Share on other sites

I would be interested to know where the tach wire is, in an xt digidash, but on the wireing harness of the dash itself.:confused:

Share this post


Link to post
Share on other sites
My '88 GL10 needed a slight mod to the green digidash to get the tach working with the EJ20G. It's expecting a high voltage (peak primary volts) from the coil primary, but the output of the ECU isn't enough to trigger it.

 

Anyway the fix is to solder a 1k resistor in parallel with resistor 112 which is a 36k resistor. This lowers the threshold voltage so it can pick up the ECU signal. Tach works perfect now.

 

Hi there, great diligence btw :) Do you happen to know if the ecu tach signal from an ej205 (2002 wrx) is the same as your ej20g? I know it's a bit dorky, but I love my "back to the future" dash and, short of getting Doc to direct lightning at me, I'm gonna make it happen :)

Share this post


Link to post
Share on other sites
Hi there, great diligence btw :) Do you happen to know if the ecu tach signal from an ej205 (2002 wrx) is the same as your ej20g? I know it's a bit dorky, but I love my "back to the future" dash and, short of getting Doc to direct lightning at me, I'm gonna make it happen :)

 

I'm pretty sure the EJ205 ECU has the same tach signal as the EJ20G ECU. I haven't worked with one personally though.

Share this post


Link to post
Share on other sites
My '88 GL10 needed a slight mod to the green digidash to get the tach working with the EJ20G. It's expecting a high voltage (peak primary volts) from the coil primary, but the output of the ECU isn't enough to trigger it.

 

Anyway the fix is to solder a 1k resistor in parallel with resistor 112 which is a 36k resistor. This lowers the threshold voltage so it can pick up the ECU signal. Tach works perfect now.

 

Dood, you rock, again! I am going to go home and try this on a buddies digi dash. I think I even have a 1k resistor as well :) Looks like you just used a 1/4 watt resistor? Shouldn't need anything bigger than that I would think. Looks simple enough.

 

I will report back if this works for me!

Share this post


Link to post
Share on other sites

huh....I wonder if that's the issue with my 4runner. Signal wire from a signal converter to a digital dash that used to get it's signal directly from the coil....

 

 

 

We tried that with the GL-10 that was just for sale here in Superior. I'm confident I got the signal wire hooked up correctly, but it did not work.

Share this post


Link to post
Share on other sites
Dood, you rock, again! I am going to go home and try this on a buddies digi dash. I think I even have a 1k resistor as well :) Looks like you just used a 1/4 watt resistor? Shouldn't need anything bigger than that I would think. Looks simple enough.

 

I will report back if this works for me!

 

 

Yes 1/4 watt is fine. Ohm's Law shows that 1/4 watt can handle a voltage of (0.25 * 1000)^0.5 = 15.8 volts. And in reality the full voltage is not dropped across this resistor, so there is plenty of margin.

Share this post


Link to post
Share on other sites

I can now report that this mod also works on the older 85/86 orange digi-dash as well. You have to put the 1k resistor across the same 36k resistor in the tach circuit but on the orange dash circuit board it's in a different location and is labeled as "R50". It's just to the left of the connector with the tach pin on the back of the board. It's difficult to access from the resistor side of the board as it is partially obscured by a permanently mounted ribbon cable so I had to remove the circuit board and put the 1k resistor on the back side of the board. Tach works great....

 

GD

  • Like 1

Share this post


Link to post
Share on other sites
I'm pretty sure the EJ205 ECU has the same tach signal as the EJ20G ECU. I haven't worked with one personally though.

 

Thanks for the reply. I did solder in the resistor. Actually I had before my original post, but I'm typically a voyeur on this forum as I see how some get on their high horse when nubies prod them:horse: However, I haven't had any luck. Just to be sure, you are replacing the coil wire signal with the ECU signal, not splicing them together correct? I realize the coil isn't "working" anymore, but didn't know if the coil could possibly still get voltage from the system and be factored in. Also the tach signal from my ecu is kicking out some strange voltage patterns. I'm certainly no electrical engineer, but maybe the ecu is f-ed up? I'm going to investigate more tomorrow. Mostly I thought I would continue the thread because, for me, the dash has been the hardest part of my conversion and I'm too stubborn to let it go and mount aftermarket parts :banghead:

Share this post


Link to post
Share on other sites
Yes 1/4 watt is fine. Ohm's Law shows that 1/4 watt can handle a voltage of (0.25 * 1000)^0.5 = 15.8 volts. And in reality the full voltage is not dropped across this resistor, so there is plenty of margin.

 

I ended up only having a 1 watt resistor, but it will be MORE than enough :) The only issue I had was that it's bigger than a 1/4 watt, so it was a tight squeeze.

 

I can now report that this mod also works on the older 85/86 orange digi-dash as well. You have to put the 1k resistor across the same 36k resistor in the tach circuit but on the orange dash circuit board it's in a different location and is labeled as "R50". It's just to the left of the connector with the tach pin on the back of the board. It's difficult to access from the resistor side of the board as it is partially obscured by a permanently mounted ribbon cable so I had to remove the circuit board and put the 1k resistor on the back side of the board. Tach works great....

 

GD

 

Yup, same procedure I did on the 88 (I think) I have. Well just about. I had to undo some bolts, and move some stuff around, but I soldered it to the back side of the other resistor. I haven't tested it yet, but I will this weekend!

Share this post


Link to post
Share on other sites

Just reporting back that the resistor trick works just fine! I installed the digi dash I did this to last sunday. It's pretty cool to see the RPM bars move :)

 

Thanks dood for figuring out what needed to be done!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×