Just lost Tach Signal...

[johnny butt]

So, I just lost tach signal in my car. I moved my ECU to run some speaker wires behind the kick panels and when I started the car back up, I had everything working in my gauge cluster but the tachometer.

I have a boost controller hooked up to the same tach signal, and it's been a while since my friend wired this up so we're not sure exactly which wire is for tach signal.

Car is a 1993 S13, motor is a 1996 RB25DET with stock ECU.

I was wondering if anyone had any ideas what wire colors are associated with that?
I.E:
Tach Signal From Motor - > ECU (??????)
Tach Signal From ECU - > Cluster (Pin # 7, Orange with Red Trace?)

Thanks.

[platez808]

sorry to hear about your issues. hopefully it's nothing too bad. are you still getting an rpm signal to your boost controller?

from what i remember and the diagrams i have, the tach signal wire is located at pin 7 but instead of yellow/red like you stated, it should be yellow with a blue trace (Y/L.) Also from what I recall, the ECU derives the tachometer signal that it sends to the tach from the CAS signal (i really dont know what wire or if it even matters.)

What I think you should do is check the ECU itself. If you need an example of what an ECU w/ fried tach signal components looks like, then just look for my thread on it hahaha. I have detailed pictures on it so you know what to look for. If it is your ECU that you're having issues with then just replace it (i have one in perfect working condition because i bought a couple looking for a solution to my tach problem before and also to have spares)

If your ECU looks fine then check all your connections to see if theyre all still good. Check connectivity between the tach and pin 7. What tach conversion are you using? If you had to custom any wiring like i had to for i30/maxima tach then make sure everything is still hooked up properly and not shorting anywhere.

Hopefully you figure out whats wrong in those two steps. lmk how it goes.

[johnny butt]

Awesome, I was wondering if Yellow/Red was right, because it is actually wired up to a Yellow / Blue wire.

I do not have a reading from Boost Controller OR Gauge Cluster Tach (which leads me to believe something going to or coming from the ECU is the problem.). I am using the OEM S13 Gauge Cluster, but everything has worked fine for 2-2.5 years, but I pulled the ECU recently and may have pulled something loose. I dont have access to a multimeter at the moment, but will be at my friends shop Sunday.

Do you happen to know the RANGE for the tach signal I should check for with the multimeter from the ECU?

Thanks for the response.


Now, to add on to the thread: I am also experiencing issues where my car will not start up without me putting my foot on the gas pedal when I turn the key. It will turn over and act like it's starting up, but bog down like it's not getting fuel. Once it is on though, it idles fine (at least from what I can tell without a TACH and only vacuum readings..).

ECU Looks Okay:


Wiring looks alright, but I will redo it when I get off of work. The white/black wire is the tach wire for my boost controller (HKS EVC 6). The blue/black wire above it is a Throttle % (position?) wire. It doesn't return any readings on the controller unfortunately. I believe it is ran to a wire that leads to the MAF, but I am not sure where else to put it? (TPS maybe?)

[platez808]

Hmm. So you were using the stock tach with no mods. Did the readings on your tach and boost controller match up? Any way, thats really weird that the signal just disappears and your ecu is fine. If anything just go nuts with the multimeter when you have the chance and check everything that way. I dont know the range for the tach signal and i'm actually out of the country for vacation right now so i can exactly poke around at my car to figure out. If you can get your hands on another working ecu then i say you try that, even if you borrow it.

In terms of the tps wiring, i'm sure that you should be taking the signal from pin 38 red wire with blue trace (R/L.) Well that is where i'm getting the signal for my AVCR anyway haha. And i was reading up on the wiring for the evc 6 online and from what i saw then the throttle position wire on the boost controller side should be white (and not white/black from what it looks like in your picture) but thats just what i read.

in terms of the other stuff.. it can be so many things.. dont even know where to start.. check the usual culprits like maf, timing, tps, vacuum leaks, fuel pressure, etc

good luck

[johnny butt]

Hmm. So you were using the stock tach with no mods. Did the readings on your tach and boost controller match up?

Yes, I know how to do exactly what LS AUTO does to convert S13 clusters to read the R33 signal. It is just adjusting a potentiometer, and matching it up with something that reads accurately. My Boost Controller and Gauge cluster were always the same within 50-100RPMS, but that is close enough for me.

Any way, thats really weird that the signal just disappears and your ecu is fine. If anything just go nuts with the multimeter when you have the chance and check everything that way. I dont know the range for the tach signal and i'm actually out of the country for vacation right now so i can exactly poke around at my car to figure out. If you can get your hands on another working ecu then i say you try that, even if you borrow it.

My ECU looks perfectly fine though, look at the 6 resistors in a row, then the 2-3 on top of that are right above it in the PIC, I believe those are for the TACH. They look okay top and bottom.

In terms of the tps wiring, i'm sure that you should be taking the signal from pin 38 red wire with blue trace (R/L.) Well that is where i'm getting the signal for my AVCR anyway haha. And i was reading up on the wiring for the evc 6 online and from what i saw then the throttle position wire on the boost controller side should be white (and not white/black from what it looks like in your picture) but thats just what i read.

Pin 38 is labeled as Throttle Position Sensor "Sense", so it that basically the OUTPUT pinout? If so, I will wire it up to that one, because it's not wired up to that currently...I think it's actually on Pin 48 (Regular Throttle Position Sensor -> input??), so I'll change that.

Also, on page 23 of the U.S. manual for the HKS EVC 6 it actually stated that the "Throttle Input Signal" is meant to be used as the BLUE wire, and the Speed/RPM Input Signal is supposed to be white. I have not changed the wires around, and like I said it all worked before, so I believe something is loose there, or maybe my CAS is going out...

Photo Attached:


I believe the lack of a proper tach reading to the HKS EVC's stepping motor is the cause of some of the other issues...

Thanks for the feedback, I will do be able to do more diagnostics Sunday or Monday.

[platez808]

yah your ecu looks fine but its hard to explain what else could be the problem. so i was just saying, to eliminate the possibility of the ecu being the problem, if you can get your hands on another one (not necessarily buy one) then it would be good. then you can totally cross the ecu off the list of possible issues. you know how it is when it comes to cars that we actually care about and work on and how they like to mess with our heads and work beyond reason and logic hahaha. i wanna say especially these damn nissans but i'm sure thats how it is for everyone else in the tuner universe.

from what i know, in terms of the tps, yellow/black and black/blue are the power and ground respectively for the tps.the middle wire which is red/blue should be the wire through which the tps sends the throttle position signal (which should vary from about 0.4v at closed throttle to around 4v at full throttle) to your ecu and in this case your boost controller. i'm also assuming that you have to set the type of tps we have on our motors (ascending) in the settings of the boost controller because that's what i had on mine, but i could be wrong.

[johnny butt]

Just a quick question, how does the ECU pick up the tach signal?

In other words, I don't have any readings coming out of Pin7, so I don't think my tach signal is ever getting from the motor to the ECU, or wherever it is it would need to go normally.

My question:
If I were to tap into a coil for a tach signal, I need to know where to send that wire so that it may go about its merry way and send the signal out of Pin 7 so I can get a tach reading on my Boost Controller and Gauge cluster again...

Thanks..