Tyson

I haven't got many attempts yet to try to hook up the tach wire of the Mychron3 Gold XG we have, but the one time I tried at the track, it didnt work. So I figured I might as well ask. We do not have an aftermarket ECU yet, and even if we did, our Gold XG does not have RS232 data capabilities, so it has to tap into the factory tach signal.

From my understanding, the blue wire of the XG harness 8-50V should tap into the blue wire from the distributor to the factory tach.

I do not like EVER cutting into factory harnesses or even stripping insulation. So I really dont want to tap into the blue wire right at the distributor. Plus, I'd rather not have another wire go through the firewall.

So I attempted to wedge the RPM wire from the XG to the back of the cluster of our 89 Civic to get a parallel signal. I was told it was the 10th wire from the center of the tach side connector. I also grounded the XG connector to the chassis. When I did this, neither the factory tach nor the XG display showed any tach reading. Factory tach just sat dead.

What did I do wrong, and what can I do next time? Unfortunately I dont have the luxury to mess around with the car before the next event. So I'd like to be sure to get it right next time. Either my technique of wedging it in the connector was bad, or maybe I'm using the wrong wire. Was I supposed to use the white wire of the XG RPM connector?

slammed_93_hatch

at the drivers side shock tower there is a blue wire that just runs into nothing. Use that.

I don't see what the problem is with cutting into the factory harness.

jlucas

I can't speak for your XG hardware but typically the blue wire at Honda ECUs is the RPM signal. You can check the documentation for your logger to make sure your on the right wire for it and the factory service manual for the correct ECU wire.

If you factory tach died, you were probably on the right wire but pulling too much current off the signal with your logger, some stock tachometers seems to be really sensitive to that. Sometimes just an inline resistor will reduce the current draw enough for the factory tach to work, other times an powered passive pickup (MSD) or isolator circuit (Race Technology makes one) is needed to do the trick.

jlucas

Cutting creates a potential failure point. Better to just shave away a 15-20mm spot of insulation with a razor blade and parallel solder your tapping wire (followed up by taping over the joint, of course).

Tyson

well at this point, im pretty sure i got the right wire. ill check continuity next time.

not wanting to cut or break into a stock wire is just a pet peeve of mine. perhaps i just need to get over it.

interesting point on the high load. im going to try wedging it again, maybe a strand grounded out or something.

someone also mentioned i should ground to the engine, not the chassis. as the sensors all ground to the engine. i grounded the RPM connector to the same chassis ground powering the XG unit. thoughts?

just a little frustrated i dont have access to work on the car. was at the track friday and it was either troubleshoot or track time. wasnt going to waste track time...

jlucas

The load I'm speaking of is internal to the logger. If that's your issue the RPM data should be in your data log even if the factory tach is not working. If you have no RPM data in data file you have a different issue.

Tyson

well the display didnt show any tach reading either. so i dont think the connection was good at all.

jlucas

http://www.aimsports.com/support/manuals.html
Looks like Pin Z should be your ECU level RPM input.

slammed_93_hatch

i ground my XG log to the chassis, and it has been working great since 07

Andrie Hartanto

It has been a while since I installed one on other Honda other than K series. In any Honda, there should B RPM output from the ECU. Use this. Then experiment with the rpm multiplier/divider to get the correct rpm.

Ground it to the chassis. You should be fine.

Tyson, I'm a dealer for AiM products. if you need any help, don't hesitate to contact me. I installed in a lot of Honda, D series, B series, K series or the 2006 Civic EX, whatever the engine code is. Additionally, NSX, EVO and others.

I don't frequent car forums a lot anymore. Feel free to shoot me an email or call me.

Tyson

thanks guys.

yeah the grounding to the chassis vs engine was just a thought. i know we still have the valvecover to headlight wire in place. so it shouldnt be an issue.

speaking of picking it off the ecu, im a little confused on that too. because i cant find what wire goes into the ecu and what kind of signal it is. it seems like it goes first to the tach, then to the ecu in a different colored wire. is it the same signal? still hook it up to the blue 8-50V XG harness wire?

i know all this would be really simple to figure out with a few tries, but i cant do anything until probably thursday morning before work, the day before we go off to the track again. thats all the access i get...

117

For my DL1/Dash2 combo, I used the ICM signal from the ECU. IIRC, it's A20 on an OBD1 ECU. I can look it up tonight when I get home.

My car is a 98, so I just tapped into the wiring in the OBD2 to OBD1 conversion harness by pulling the pin in the connector, cutting the insulation in the wiring in two places using a set of wiring strippers, then used a razor blade to cut the insulation off between the two cuts. I wrapped the wire used for the tach signal around the harness wiring, soldered it in place, then covered with sealed heat shrink (hence the reason why I had to remove the pin from the connector). I never cut the wire, so it's as good as OEM, IMO.

No problems with the tach signal, and the tach in the dash works just fine, although I'm getting rid of it soon since I use an RT Dash2.

EDIT: Looks like it's A20 on the OBD2 connector and A21 on the OBD1 connector, see here: https://honda-tech.com/forums/honda-civic-del-sol-1992-2000-1/faq-need-ecu-pinouts-then-look-inside-478377/

I'll verify tonight when I can look at my own wiring diagrams.

Tyson

what about OBD0?

117

Good question. I don't have any experience with OBD0, but here's what I found:

Looks like the Ignitor Unit (B15 & B17) would be a good candidate here (ICM = ignition control module, so perhaps the ignitor unit is the OBD0 equivalent):
http://hondaswap.com/reference-mater...pinouts-28667/

Same one here (B15 & B17) called the ignition output signal:
https://honda-tech.com/forums/honda-crx-ef-civic-1988-1991-3/obd0-pr3-ecu-pinout-question-2263486/

I have no idea why there are two outputs, though.

So take those with a grain of salt, as I don't have direct experience with OBD0.

Tyson

i wonder if i could tap into the VSS signal too....

i havent even gotten the AIM software to communicate yet. but reading the manual it seems i can configure and calibrate the number of pulses to match the VSS signal from the speedo. instead of sticking the magnet on the axle.... can anyone who uses the software confirm?

117

Yes. I tap into the VSS for my Dash2's speedo reading (so that the odometer works), but I've found that the VSS signal is "unreliable" for some reason. In other words the speedo reading (which is digital) isn't smooth like the OEM analog speedo, and it's not smooth like the other digital speedos like in the S2k or new Civic. If there was a way to damp the signal via averaging like you can on the other inputs (like oil temp, oil pressure, etc) it would make the speedo much more useful.

I can always use GPS for the speedo, but then I lose the odometer function.

I can find out how many pulses per mile my VSS is, but like I was saying, mine is a 98 Prelude. I'm not sure how different yours would be.

slammed_93_hatch

yep works just fine.

Tyson

even on OBD0 where the VSS originates at the speedo cluster itself? just checking.

117

Looks like B16 on the ECU from the links I posted above.

Tyson

well i cut the insulation and soldered the wire on to the tach at the back of the cluster. it reads 2x higher, but i havent configured the software yet... its configurable, right?

the downer is that i tried to set up the wheel sensor. the magnetic one with like a 8mm fine threaded stud at the end that picks up the magnetic pulse. and it just doesnt read... i dunno why not. its just a dumb hall effect sensor. only 90 minutes to work on the car today.... oh well. might have to buy a new sensor.

slammed_93_hatch

it has been a VERY long time since i setup mine, but you don't need that sensor, nor any wheel speed sensor to get mph.

Tyson

you probably hooked it up to electronic VSS.

mine has a dedicated channel for wheel speed.

im not sure if i could just rig up my own to the wheel speed channel since its looking for a single discrete pulse every revolution.

Andrie Hartanto

Tyson, the rpm is configurable through the software or the dash. The wheel speed sensor can be tapped to stock vss. It gives 5 pulse per revolution IIRC.

there are two speed sensor input on xgLog. Make sure the input wire corresponds to the right lead wire. The sensor that comes with the unit uses white wire or pin 1. The other input is the green wire.

Tyson

yeah, my unit isnt an "XG log", or even "Gold", its "Gold XG".

looks like this. look carefully at the number of channels. it took me forever to figure out it was neither an XG log or Gold.


but perhaps i can hook it up to VSS with a spare connector i have and make my own harness if this thing really is dead. hard for me to believe... its just a stupid hall effect sensor.

Andrie Hartanto

So you have the junction box or just the display? Do you know if you version is kart or auto ones? This will make quite a difference. Becareful when making your own wiring from existing cable. Check continuity.