Tachometer Issue! S14 - 2015

[Zenkipowered]

Already read up on these threads from the past found on Zilvia:

RPM/Tach signal issue
http://zilvia.net/f/showthread.php?t=51585

96 S14 Tach Issue
http://zilvia.net/f/showthread.php?t=448700

Sr20det Tach signal issues
http://zilvia.net/f/showthread.php?t=142203

So I Beleive I Just Solved The Infamous S14 Tach Glitch
http://zilvia.net/f/showthread.php?t=355077

These threads have been useful on some insight but let me explain the issue I am having currently:

I had my 1997 240sx with an S13 Black top SR20DET, receive a 2 way alarm install with auto-start/turbo timer capability. Viper 2 way alarm don't know the model. At a local security and alarm shop. However after the alarm install the stock tachometer stopped functioning. The Tachometer functioned normally for years until the alarm install.

I didn't mind much because I had just received my Defi BF standalone Tachometer and figured, with this in the s14 I won't care if the stock one works anyway.

Friend and I tried figuring out why the tach won't get any signal. We found the yellow/red wire and the pin in the ecu and tried tapping into it directly but there was no signal. occasionally the tach would peak out at 9000 RPM then quickly go back to 0 RPMS on the tach.

The next strange thing is that there is voltage coming out of the ecu signal wire, but it reads at 14volts! which shocked me. because iirc its suppose to read from 1.5-5 volts? correct me if i am wrong.

The next puzzling thing is that the Apexi AVCR and POWER FC commander both have the tachometer readings displaying and accurate. Just the analog OEM tach and Analog DEFi tach does not read anything?

The back of the cluster tach wire has a signal or voltage but again its 14v (this i have to check again but out of the ECU it is 14volts for sure). Is there something else I can do to check and figure out what is going on?

I have tried connecting the signal wire directly to the tach and nothing. I am running out of ideas.

Possible reasons for not working that We have came to is:
-Alarm shop might have touched something they should or shook off a wire loose?
-ECU converter or whatever is called for the pin is busted?
-Wiring harness needs to be replaced or tracked down to find a loose connection?
-Tach was working fine since alarm day which was on May 25th 2015. but could possibly be the tach?
-needs to have the "connecters" on the back of the circuit board re-soldered?

any help would be greatly appreciated!

sorry for the long post

[dbeiler]

Friend and I tried figuring out why the tach won't get any signal. We found the yellow/red wire and the pin in the ecu and tried tapping into it directly but there was no signal. occasionally the tach would peak out at 9000 RPM then quickly go back to 0 RPMS on the tach.

The next strange thing is that there is voltage coming out of the ecu signal wire, but it reads at 14volts! which shocked me. because iirc its suppose to read from 1.5-5 volts? correct me if i am wrong.


This is confusing information. What do you consider the ECU signal wire? Clarify please.

It sounds like the tach section of the gauge cluster has finally called it quits. Thankfully, these crappy old cars have a very simple electrical system that allows for easy diagnosis with only a multimeter.

Remove the gauge cluster.

With IGN on, check for gauge operating power at Pin 21 of the M15 gauge connector.
You should be getting 12+ volts or whatever your battery voltage is.
If the rest of your gauges are working, you already know this pin is receiving power.

Check the tach ground. Check continuity from Pin 22 of the M15 gauge cluster to ground.

With the engine running, measure voltage at Pin 12 of the M15 gauge cluster. This takes the place of measuring voltage at the Yellow/Red ECU wire. If I remember correctly, 4 cylinder tachs read 1K rpm per 1 volt. You should be seeing approximately 1 volt per 1000 engine rpm. Hence, 5000 rpm should give you a 5 volt reading.

You noticed no voltage when you previously checked the Yellow/Red wire. Maybe you checked the wrong one?

If the wires check out fine, you can attempt to resolder the gauge cluster. Or just throw in it the trash and buy another one like I usually do.

[Zenkipowered]

This is confusing information. What do you consider the ECU signal wire? Clarify please.

It sounds like the tach section of the gauge cluster has finally called it quits. Thankfully, these crappy old cars have a very simple electrical system that allows for easy diagnosis with only a multimeter.

Remove the gauge cluster.

With IGN on, check for gauge operating power at Pin 21 of the M15 gauge connector.
You should be getting 12+ volts or whatever your battery voltage is.
If the rest of your gauges are working, you already know this pin is receiving power.

Check the tach ground. Check continuity from Pin 22 of the M15 gauge cluster to ground.

With the engine running, measure voltage at Pin 12 of the M15 gauge cluster. This takes the place of measuring voltage at the Yellow/Red ECU wire. If I remember correctly, 4 cylinder tachs read 1K rpm per 1 volt. You should be seeing approximately 1 volt per 1000 engine rpm. Hence, 5000 rpm should give you a 5 volt reading.

You noticed no voltage when you previously checked the Yellow/Red wire. Maybe you checked the wrong one?

If the wires check out fine, you can attempt to resolder the gauge cluster. Or just throw in it the trash and buy another one like I usually do.



sorry, I meant the yellow / red stripe wire is what I am referring to as the tach signal wire. It has voltage but its outputting 14v. I understand it should read 1volt to read 1000rpm,but I'm worried because as mentioned its putting out 14v. I will check this again later when I get my car back as it is now in the process of being shipped to my next location.

However, Even if the OEM analog tach doesn't work that is fine because I want to use my Defi tach. However the defi tach is tapped to the wires feeding out the back of the OEM tachometer, and the defi tach doesn't work either.

So my conclusion is that there is no signal coming from the tach wire at all? but then occasionally there is and it peaks the gauge out. By peak i mean the RPM needle will go into the redline and then drop back to zero rams.


Im starting to assume that maybe a ground wire like you mentioned could be loose? or the ECU pin for the tach wire is bad? Either way I will double check and report back what I come across.

Any more ideas or things i should check for would be helpful.

[R3cK]

also got the tach problem. euro s13 with ca18 swapped to sr20 redtop.
already put in a completely new car harness. checked ground, 12v, new ecu, new cluster. nothing. also checked CAS as descriped in the manual. no clue whats wrong.
put in a resistor, which worked for my buddy with the same swapp.
heard about puls and non puls cluster. -90s and +91s years. dunno. i know about SOHC and DOHC but this is a KA24 thing only.
RPM ecu signal is around 5.1V or 5.2V puls signal (cant measure the frequency but when i throttle up, the voltage doesnt go up, so i think it is puls)