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standard ECU

rsx84

By rsx84,
in Engines & Forced Induction

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rsx84 Veteran

rsx84

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my r32 rb20det has no rpm signal from the ecu? this was confirmed by the auto elictrican who fixed up some other bits for me, i have two questions

1st is can this be fixed without replacing the ecu?

2nd is will this effect the install of my safc

the sparkie said he can get the signal from somewhere else

oh yeah the engine isn't in a r32 anymore...

Cheers Matt....

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rsx84 Veteran

rsx84

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What exactly is the problem?

I think someone has this arse-about. If anything, the engine generates a rpm signal for the ECU.

from my understanding the ecu rpm signal wire is linked to the tacho, thats what i'm talking about, from the ecu to the tacho theres no signal at all which is why i'm concerned about the safc install as well...

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joh21m Collaborator

joh21m

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My ecu didn't produce an rpm signal until i'd replaced my s13 tacho mechanism with the r32 mechanism. I still had my SAFC installed before then though, can't remember if i'd had it tuned before i fixed the tacho.

how exactley do you go about replacing the mechanism? i have the exact same problem, my tacho reads very slowly...

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rsx84 Veteran

rsx84

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My ecu didn't produce an rpm signal until i'd replaced my s13 tacho mechanism with the r32 mechanism. I still had my SAFC installed before then though, can't remember if i'd had it tuned before i fixed the tacho.

toward that it's a simple 4 cylinder tacho mechanism (180sx) getting a six cylinder pulse from the ECU, voltage is different or something, when it came to the SAFC the rb20 ecu had a signal that went to the safc where as my rb20 ecu just dosen't have a signal at all, sorry mate thanks for the help though..

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browny Proficient

browny

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The tacho signal wire (pin 7) generates a signal by shorting to ground through the ECU.

If you were to connect this wire to an oscilloscope (and nothing else), the voltage waveform would be a flat line at 0V, ie the pin is being switched by the ECU between ground and 0V.

To get a signal other than a flat line, you need to connect a voltage source to pin 7, so then the ECU is switching pin 7 between (say) 12V and 0V and therfore generating a square wave.

I'm pretty sure the gear that provides a voltage source to pin 7 is integral with the OEM tacho and I think this generates a 0-5V waveform.

Also different tacho's are deisgned to work with different voltage waveforms, some are universal but others are designed to work at say 12V or hundreds of volts (ie direct from the coil).

You can generate a 0-12V square wave by connecting pin 7 to a 12V rail. Because no-one knows the current limit of the circuit for pin 7 a pull up resistor of say 10k ohms is usually connected between the 12V rail and pin 7. This limits to current to a small amount so you don't burn out that part of the ECU.

The pull up resistor method will only work for tachos which can use a 0-12V signal tho and it won't solve your problems if you need to modify the frequency of the pulses for different cylinder engines. If the tacho doesn't work, you will need a device that can generate a voltage signal that your tacho can read. These are commonly referred to as tacho boosters. Sixworks in Newcastle sell these devices (approx $50 or $100 depending on which you need).

These take about 5 min to install, I can put you in touch if you like.

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BBQ Community Regular

BBQ

Posted
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What I remember doesn't agree with any of your comments. I'll check my service manual when back at home.

BTW, my comments are all for the R32 RB20DET.

Sorry, I was looking at the r33 Pinout diagram, The 32 Diagram for Rb20,

Pinout put 7 is Speed Sensor, which yes you can use for the RPM Signal.

Thats the problem with having too many Wiring Diagrams !!

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rsx84 Veteran

rsx84

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my question was for the r32 rb20det, http://www.rb20det.com/ecupinout.html thats a pinout diagram for the r32 ECU,

if i can get the tacho to run from somewhere else on the engine would that signal be ok to hook up the safc to aswell?

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BBQ Community Regular

BBQ

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my question was for the r32 rb20det, http://www.rb20det.com/ecupinout.html  thats a pinout diagram for the r32 ECU,  

if i can get the tacho to run from somewhere else on the engine would that signal be ok to hook up the safc to aswell?

Yes just tap into that wire pin out from the ECU with your SAFC and that will give you a reading for your RPM, Simple as that.

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rsx84 Veteran

rsx84

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Yes just tap into that wire pin out from the ECU with your SAFC and that will give you a reading for your RPM, Simple as that.

the thing is is that wire from my ecu has no signal at all, its dead, been tested by two auto sparkies now and told no signal....

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