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RB20det Tach install...

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solo
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RB20det Tach install...

Postby solo » August 4th, 2006, 8:46 am

I want to install a monster tach on my rb20det. Did some research, found out that wire #7 from the ECU (yellow and red) is responsible for tacho signal. Tried it, no luck. Did further research, and came up with guys who installed a "10k value resistor" between the signal wire and a 12v supply and it worked. I'm a little confused by this...:?:
Anybody here ever did this install and care to share their secrets? Other than that it's over to the electrician on the weekend.....

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Postby Dave » August 4th, 2006, 8:56 am

they usually use the msd dis tach driver for a clean signal

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Postby solo » August 4th, 2006, 9:02 am

^^^Agreed. But it can be installed without the Tach adaptor. These guys at this Forum http://www.zerotohundred.com/newforums/ ... -1677.html have an ingenious way mapped out, but I want to know if locally it's done any different....

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Postby dry » August 4th, 2006, 9:38 am

from what that link says, hit him some of this:

Code: Select all

tach signal from ecu ----+----> tach
                         |
                         -
                         - 10 Kohm
                         -
                         |
                         +---[ 1A fuse ]----- +12V


that way you'll get a 12V square wave, since the ecu grounds the pin7 with each ignition pulse.

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Postby solo » August 4th, 2006, 9:45 am

dry wrote:from what that link says, hit him some of this:

Code: Select all

tach signal from ecu ----+----> tach
                         |
                         -
                         - 10 Kohm
                         -
                         |
                         +---[ 1A fuse ]----- +12V


that way you'll get a 12V square wave, since the ecu grounds the pin7 with each ignition pulse.



I know I could count on mad people like you to understand this. Thanks Dry.

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Postby ninjaboost » August 4th, 2006, 12:44 pm

:shock: WTF!!!

...solo please let me know if this works...

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Postby solo » August 4th, 2006, 12:49 pm

ninjaboost wrote::shock: WTF!!!

...solo please let me know if this works...


There's a lot of questions on this subject on the RB forums, and the answers are all similar to what Dry explained. Check this diagram offered as well....Image

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Postby megadoc1 » August 5th, 2006, 1:09 am

great info there just tried using that signal myself with no luck
i now understand what was going on there
this is easy

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Postby Carrot » September 12th, 2006, 3:10 pm

aye, now trying to hook up a tach in an AD wagon. Wasn't getting it to work. Will this work with my car?

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Postby Chiney » September 12th, 2006, 7:49 pm

^^ qg15de?

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Re: RB20det Tach install...

Postby vct17inch » August 24th, 2017, 2:29 pm

Many years later. I just tried that 10k ohm resistor thing. It didn't work. So many possible problems to now consider. I wanna see someone try that resistor trick and get it to work

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Re: RB20det Tach install...

Postby Ronaldo95163 » August 28th, 2017, 2:15 pm

You tried wiring it up like in the diagram solo posted?
Not sure what wire 49 does ( I don't have a RB). It could be a constant 12V

But from the diagram it looks like the 10k resistor is a pullup resistor. ie it pulls the signal wire up to 12V when the output from the signal wire is floating. When the output goes low (to ground) the green signal wire would be at 0V. So you'd have a PWM signal being generated, oscillating between 0-12V.

Check and see if it have a signal wire from the OBD port as well. Was like that for my rolla and I just pulled the signal from there.
You could test the signal wire with a multimeter btw. Just make sure to set it to AC and once you rev you'd see it increasing.

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Re: RB20det Tach install...

Postby Dave » August 28th, 2017, 2:19 pm

Sometimes the signal from the ECU output isn't strong enough for a splice in and may need a tach adapter to convert the signal for an aftermarket tach

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Re: RB20det Tach install...

Postby vct17inch » August 28th, 2017, 4:17 pm

Ronaldo95163 wrote:You tried wiring it up like in the diagram solo posted?
Not sure what wire 49 does ( I don't have a RB). It could be a constant 12V

But from the diagram it looks like the 10k resistor is a pullup resistor. ie it pulls the signal wire up to 12V when the output from the signal wire is floating. When the output goes low (to ground) the green signal wire would be at 0V. So you'd have a PWM signal being generated, oscillating between 0-12V.

Check and see if it have a signal wire from the OBD port as well. Was like that for my rolla and I just pulled the signal from there.
You could test the signal wire with a multimeter btw. Just make sure to set it to AC and once you rev you'd see it increasing.

Yeah wire 49 is a constant 12v voltage and the 10k ohm resistor is a pull up resistor. Wired it exactly as the wiring diagram. And no response on the tach. No obd2 port on the car. The rb20det was transplanted into the vehicle

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Re: RB20det Tach install...

Postby vct17inch » August 28th, 2017, 4:21 pm

Dave wrote:Sometimes the signal from the ECU output isn't strong enough for a splice in and may need a tach adapter to convert the signal for an aftermarket tach

To be honest this makes more sense than the instructions on the tach adapters instructions I've read. Their instructions said to tap the +12v power of a coil pack to get the signal. I thought that was constant +12v and the signal wire for the coilpack would then close the circuit like a relay. I didn't know the +12v positive also pulses on each firing

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