Finding the elusive VSS
 

Hello there

I am really interested in the MPGuino, but first of all I wanted to know if there is a universal method to finding the VSS cable/s in any car with electronic ignition? I have a 1995 Alfa Romeo 146 with the 1712cc 16v boxer engine, a car which is not well documented, I don't think it was sold in the US. The only specific information is that the OBD has a Bosch protocol, something prior to version M.2.10.3.

So you can see I don't have much to go on! Is there any hard-and-fast tricks to find the VSS cables, such as tracing them back to the speedometer? I haven't pulled the dash out (yet). I noticed on the MPGuino wiki there was a line saying...
I've know idea where this Technical Support is. That's why I've come to you guys! Any suggestions would be appreciated, thanks.

There are some links at the bottom, one is to a rostra site that sells a cruise control device in the states, but there are no alfas in it.

Can you locate a schematic for your car (online picture or manual) and post it?

After some googling: www.autokomputer.pl/download/speed_pulse_locator.xls

It has a 1994-1997 AR 145 listed right at the top. Yours should be similar. You can also look for guides for after-market cruise control modules.

Furthermore, you can try (physically) looking around on the transmission for something like a 3 wired plug going in near the differential. This would likely be a VSS.

Welcome to ecomodder!

Thank you guys! I will attack the dash this weekend and see what I can find/irreversibly damage.

I will also look around for a wiring diagram and post it up, it can't do any harm. However my Googling abilities are nowhere near as good as Mr Socket's...

I think there is a haynes manual for your car too (library? Ebay?) and the local alfa dealer should know where to find a speed signal if there is one.

How about the same question "Finding the elusive VSS" on a '89 Geo Metro?
This should be easy. Every one has done this to their Metros right?
The info I find id's a yellow/green wire under dash near fuse box. My Haynes manual says this is rear defrost relay.:confused:
Haynes manual has no detail about ECM, only general harness and wire info schematics.

I found my car's wiring diagram after MUCH searching online. It was in a manual for my car. It had a wiring diagram for the ECU (Engine Control Unit, the computer) and showed where the VSS, INJ, and many others were. I got under the dash, pulled the wiring harnesses off, and... they weren't the same as in the manual! I wound up jacking up the front drivers side tire and measuring ohms between each of the wires and ground while turning my tire. It worked, it was the green and yellow wire and the second to last one tried. You know it's the vss because the ohms will go from 0 to infinity and back several times during a revolution. I found the injector by comparing the color of the wires at the injector to those near the ECU and tapping into the injector from under the dash. My 12v came from the fuse box (though I think I may switch it to from the battery since I can't use my high beams with it) and my ground is just grounded to the chassis. I would guess I searched for the wiring diagram for several hours, and actually doing it with the method above took about an hour.

EDIT: I should add, the injector has two wires running to it, with the key on (not engine running) unplug the injector and measure both wires, one is 12v the other is 0v, tap the 0v one. Mine was yellow, maybe with a black stripe.
Also, I think these methods are covered in post #1 of the MPGuino page.

wyatt

Thanks for the info.
I've already got a good injector signal I used with my recent tach install.
I'll give it a try with the wheel spinning thing for VSS.
When I measured my green with yellow stripe wire with the engine on, it had 14 volts. That doesn't sound like what I'm looking for. Must be a different color on the '89?
Seems like I've read looking behind instrument panel for where spedo cable plugs in. Does this sound reasonable also?
Thanks, I'll start digging

Edit: my first sentence is unclear and just plain wrong. I used ignition coil -gnd for tach install but found the injector signal on the TB where it should be for the MPGuino hook up.

I think you could find it that way, but for me at least it was faster to use my voltmeter to test the wires while turning the wheel since I already had the wiring harness pulled off. I pretty much hope I never have to pull those again... what an unnatural position with my feet in the air, head on the floor, and trying to maneuver my hands up behind the dash... That being said, it really didn't take too long.

wyatt,
You give me confidence. Thanks!
I think I remember that position from when I replaced the heater core.:eek:

I was picking up a haynes for an s-10 at the library and thought to look at the metro book. It said vss was yellow with green stripe. It hooked up to the upshift indicator, etc, from the little switch behind the speedo.

Edit: it is yellow w/green stripe in a 98 too:
Metro - EcoModder

Hey thanks dcb. I'll grab that one and measure it. I appreciate the location info also. Sounds like less time on my head.

go2guy had an older metro as well, said he found the ecu/vss under the dash on the drivers side, above fuse block.

It would be nice if more people took pictures and posted them on the wiki (hint) ;)

In my 95 Neon, I was afraid to pull apart the wires to the PCM/ECU. Fortunately I have a factory manual, so I removed the instrument cluster and tapped into the harness where the VSS signal goes into the back of the cluster. Only one wire comes through the firewall - from the #4 injector. Would have been more afraid of the airbag going off, but I disconnected the battery first ...

OK, I found it (VSS)!!! Hint taken...picture taken
 

Thanks for your help and encouragement guys. I found it!!!
After I read the WHOLE MPGuino workspace one and re-read other helpful posts I got busy and did some digging. I read it all because I needed background and info for other things also (programing related). I had posted earlier (in error) that I tried green/yellow. In fact I did get the yellow/green (just typed it wrong) as suggested but it wasn't this yellow/green wire I was looking for (oh Obie Won). Ok so patience and perseverance shows that that there might be more than one of these color wires doing something else.

dcb- not sure if this photo is wiki worthy. A photo of last nights spaghetti dinner might do better. I will at least put an up date on wiki about the possible of more than one wire color in the same general area.

http://ecomodder.com/forum/emgarage-...8547aa2611.JPG

Edit: Ok, I don't know how to post photos. It is in my garage area.
http://ecomodder.com/forum/emgarage-...8547aa2611.JPG

Lol, thx. I can clean it up and add it to the metro page (make text white might help) in a section about older metros perhaps. Or if you want to take a stab at it that is fine too, on the left of that page is an "upload file" link, you upload it, give it a name to use in the wiki, then use the image syntax for the other images to make it display. We can roll it back if it gets totally hosed, don't sweat it :)

Just wanna say thanks for the advice I've gotten so are in this thread and on this forum.
Based on the spinning wheel trick I was able to confirm that I found my VSS (1991 Geo Metro). MPGuino also has good power and I seem to be getting fuel readings.
Trouble at this point is very intermittent data for speed. This weekend I'm going to try to make all my connections more securely and see if that solves this problem.
Speed will register accurately for a few seconds, then cut down to zero, only to come back from time to time.

If that's the only problem you are having, you may want to check all the solder connections on your board, and specifically the ones along the VSS line. When I soldered mine up I had missed one connection (or rather, it didn't make a solid connection when I soldered it the first time). Your board may be perfect, but it is something to keep in mind.