Speedometer / VSS issue.

[lakefxgp96]

Ok goiing to try and make this short to see if anybody knows whats up.

 

EDIT: This is in the 93 Lumina 3.4

 

Not long before i switched out to the '90 cutlass digital cluster, I had a power steering pressure line burst. I fixed the line and to test the car I reinstalled the original cluster. Everything worked on the cluster except the speedometer. Somehow after messing with it i blew the 'indic' fuse and replaced it. Put it back together and still no speedo. figuring i had broken it somehow, i went ahead and wired in the new cluster. Since then everything works on the new cluster except the speedometer. After a little test driving, i have all of the symptoms of a bad VSS, no 4th (OD)gear, no cruise, no trip od or speedometer.

 

I replaced the VSS with one i knew to be good, no change. So today i took a multimeter and tested all the continuities between the cluster and the ECM. Green wire is good all the way to the ECM (tested both green ones) I know i didnt switch the green wires because the temp sensor/guage is working fine. Yellow and purple wires from the VSS plug back to the ECM are fine. No fuses are bad either.

 

What gives? any thoughts? I really really appreciate your help. Thanks!

[joey b]

the VSS I think is just a magnet which gives a pulsing of voltage (or resistance), much like the crank sensor. There is a spot inside the transmission which gives a different voltage (or resistance) reading. The faster you drive the faster the readings toggle between high and low. Get a harness, unplug the VSS and wire in your harness, run the wires to the inside of the car and get a voltmeter, maybe an ohm meter (one or the other) and drive. Note any changes.

[lakefxgp96]

Actually its a pulse from what i understand. I would guess i'd need an oscilloscope for that... but what is the signal from the ECM? probably ohms, so you might be correct right there.

 

 

I called my uncle who is a mechanic, he thinks its the ECM. i'm not convinced of that either but i guess i could get a 93 ecm, put my memcal in their and try it...

[lakefxgp96]

Ok in light of that idea, here is some more information.

 

I tested the Speedo signal wire against a ground on the car.

 

With the car off, i get a full "0.000" continuity, or no resistance in other words. Meaning the wire is basically grounded.

 

In key-On, i get "1.000" continuity which means no signal or voltage at all. While driving, it stays at 1, which means to me that there is no signal coming from the ECM. This doesnt rule out there is no signal going into the ECM though... Tomarrow morning i will see if i cant find a signal coming from the VSS or if its somehow shorted or grounded out.

[mfewtrail]

The VSS is a magnetic reluctance style sensor, it needs to be checked with a voltmeter that can read AC voltage. You can remove it from the car and hook up the voltmeter leads to test it, then turn the small drive gear on it to see if you're getting a fluxuating voltage reading from it(the reading will be pretty small, it should also be constant and close to the same range).

 

 

EDIT: Hit enter too quickly. Micheal, you can also test the VSS w/ an ohmeter as well, maybe someone else here knows what values you should be looking for when testing either the voltage or resistance of the VSS(either that, or I'll dig through my old junk and try to find the specs for you in one of my service manuals).

[lakefxgp96]

I'll give the a/c voltage trick a try. both of my VSSs which i think both are good, are reading in at .133 and .131 at 20 m ohms range.

 

 

What do you mean turning the small drive gear? just spinning the tire in the air kinda thing?

[mfewtrail]

I'll give the a/c voltage trick a try. both of my VSSs which i think both are good, are reading in at .133 and .131 at 20 m ohms range.

 

 

What do you mean turning the small drive gear? just spinning the tire in the air kinda thing?

 

If you remove the sensor itself, the end that goes into the transaxle has a small gear on it. You can spin the wheels and do it that way(with the sensor still installed), but I believe you need to have someone hold one of the wheels stationary while you spin the other wheel(with the transaxle in neutral).

[lakefxgp96]

Well its getting to be trickier.

 

It appears the VSS is working flawlessly. I tried what you suggested, fewtrail, the A/C voltage climbs from 0.0 to 0.1 etc as the speed of the wheels increases! Ohm's change erratically as the wheel turns and is aways at 0.133 at rest using the 20 k range.

 

So as it looks now, there is signal to the ECM, but there is no signal out of the ecm. its starting to looking like a bad computer, is there anything else i can check?

 

Thanks!

[lakefxgp96]

I checked the values on the DRK GRN speed signal wire to the cluster, i checked Ohms, Amps, Volts AC and DC, nothing moves like it should. man this bugging the crap out of me!

[LukeZ34]

I'd swap your ECM out with another one.

When my ECM took a shit, the speedometer stopped working, and it had a hard time starting and running too. If you can pick one up cheap, may as well give it a try.

[slick]

Sounds like a faulty ECM. But, if that doesn't fix it, I wonder if there is a short somewhere in the dash from the cluster swap. If so, I'd just run a new line up to the ECM, and call it a day.

[lakefxgp96]

Thats a reasonable idea too. I don't think its shorted to the cluster, but perhaps inside the cluster its shorted and its feeding the other devices (cruise, etc) a wrong value. Im going to try running the cluster without any signal from the ecm and see what happens, if not then i'll just go pick up an ECM.

[lakefxgp96]

Ok the mystery gets bigger.

 

 

I replaced the entire VSS signal wires (yellow and purple wires) all the way to the ECM and even used a different VSS plug that i stole off my old 3100 harness.

 

No fixxy.

 

 

So then today i replaced my ECM and inserted my eprom into it. still no good. I still have no speedometer.

 

 

The last thing i can think to do is drive around without the cluster installed and see if I have all 4 gears and cruise. if neither work im going to be at a total loss...

[lakefxgp96]

oops :oops:

 

I figured it out. when i rewired that 'new harness' for the vss, i accidently reversed the pins on the connector somehow. I switched back to the original wires on the harness since it is ran correctly already, then wired it back in. Now i have a speedo! cruise is back and so is 4th! wooohooo! not bad. for some reason, with the new ecm i got, the engine runs smoother and even has more power in the lower end, i wonder what else was wrong with that computer....im not complaining now though...

 

It cost me $25 bucks to fix this altogether, imagine what all of that testing and trial and error would have cost me at a shop! I made my money back anyway though, i found a broken tool tray inside of the car i grabbed that ecm from, inside it were 3 craftsman sockets, an 18 mm wrench and 1/4 crafstman rachet with the UPC code still on it! this thing has never been used i don't think. Time to party!

 

Now that i have the new ub3 install, i have a working trip odometer and a working fuel guage. this has been the most rewarding mod i have ever done (well besides the l67swap in the GP of course )