Help with wiring on Pin 1 of DLC or black wire on X20/X16

[yokoseiki]

I did a stupid thing I think. I've been slowly thinning the wiring harness and now have a weird issue.

Currently I have my Racepak Dash hooked up to "black" wire that goes to the stock tach. After doing some wiring now the stock dash and DAQ reads 0 RPM with the car running. However when I unhook the DAQ the stock dash comes back.

I only need help with 1 thing. Can someone measure on an M3 or Z3, doesn't really matter, the voltage you get on Pin 1 of the DLC. (Same black wire) When my car is off, I actually get 3V. I don't remember ever getting voltage. I can only assume it's coming from the EWS ??? Is this normal? How could it be? Ecu is off and this wire is supposed to be pulsed 5V no?

If this is normal then it's the DAQ box that's grounding out the pulse. It's possible I suppose. I already messaged on member here and he thinks I did something funky or it's the box. In a depserate attempt to get RPM for my next track day I order an MSD tach driver that will give me a 12v pulse. Thought about using a signal wire for an injector or coil pack but I didn't want to cause a misfire if my box is jacked up. Rather the car just shut off for example if the MSD box goes bad.

[ScotcH]

If you only care about RPM on the Racepak, you can do that without the stock cluster ... just run the wire fron the ECU (or your X20 connector) to thge dash, and forget about the stock cluster. The signal comes from the ECU.

[yokoseiki]

I just don't have time to mess with it right now. As a diagnostic to see if it's the harness or anything else I'm thinking I might cut the black wire from the ecu and wire it directly to my DAQ box and see if that makes it return to normal. If it doesn't then I know it's the DAQ box.

Thinking about it now, since my voltmeter automatically adjusts the range the voltage I might be reading could me .3 or .03 volts. I have to double check again.

[drken]

Wow, this is weird. I am having the same exact issue, but with my RLC Racing data system! With the data system "on", the stock dash reads like normal (tach and econometer). With the data system powered "off", I get no tach or econometer movement. It's like (for lack of a better description) the data system is "stealing" the tach signal before it gets to the dash. The data system tach wire is tapped into the tach signal wire between the DME and the gauge. I am wrapping up an S52 swap into my E30, but my testing so far shows the same issue, whether using the M20 DME (Motronic) or the S52 DME (MS41.1), so I don't think it is a DME issue. I thought I'd try connecting the data system in different ways: placing the tach sensor wire in a different place, like the data port connector, or grounding the tach input separately, etc... Any electronics expert types have any ideas about this? It's not critical, but it would be nice to know that everything is working " right", with gauge readings correct whether data system is on or off.
Thanks!
Ken

PS: I'm using the " general ground" of the data sytem for the tach signal ground. The data system tach input wire has a separate ground available, but I have not used it yet. Would that make a difference, and if so, where would the best place be to connect it?

[yokoseiki]

It kind of makes sense as your car is a swap so you have a wiring harness that probably doesn't have everything hooked up either.

I know it works because that is the way I've always had it and it worked fine. Almost everyone uses this wire or Pin 1 on the DLC.

My DAQ box is designed for 5-18V so if the signal only comes up to lets say 4.5V, the car should run fine, and your DAQ box will not just like the way mine is now

If I have a miss or problems with the ABS I'll fix it but for now I'm leaving it...

[yokoseiki]

Was a bad wire going to the DAQ. Fixed!