VSS problems - Need help (like yesterday)

[frostydevil]

Hey guys, what do ya think? I had the tranny rebuilt 3k ago and it was awesome for a time with the corvette torque converter up until a couple weeks ago. Now I had a problem occuring where the computer finally threw a code indicating a VSS problem. Taking it back to the shop because they did the original work on it, they replaced the VSS, and it still isnt giving the ECM a signal. Could this be a wiring issue, or more likely the ECM needs to be replaced? Would anyone happen to have a OBD1 LT1 ECM they would be willing to part with so I can find out? Thanks guys!!

 

[frostydevil]

found a few ecm's in a "you pull it" yard for $40. cant beat that. Lets see if this helps. Otherwise I just might end up running new wire from the VSS to the ECM. Today has just been hell.... I designate the magic word for the day to be : "F*%K-IT!"

Quick...I'm not at home, so I dont have the tools, and I want to stop at the yard to pull the ECM before I pick up the car from the shop that cant fix it. What tools should I bring from work in order to pull an ECM? Thanks guys!

 

[frostydevil]

Ok, replaced the ECM. and it didnt fix the issue. I have no speedo, no working odometer and no working trip meter. The tranny doesnt want to shift out of first and when it does, it lurches into 2nd and throws two codes for the VSS, then enters limp mode. Anyone know the pin-out on the ECM for the VSS. I want to replace the wiring for the VSS....thanks!

 

[Buffman]

Probably best to post on ISSF to get results from the trans experts

 

[dwardo]

What's the advantage to the Corvette torque converter? Inquiring minds want to know?

 

[Buffman]

One of them is higher stall than the stock one, but are you sure you don't have the Corvette servo and a stock torque converter? I didn't think the vette converter stalled higher enough, it was the s10 one that's 2200rpm

 

[turbostar]

Frosty,don't know what yr your car is but this is from my 95 service manual. There are two wires from the VSS.The yellow wire,which goes to the "b" terminal on the vss goes to pin a32 on the ecm. The other wire ,which is purple,goes from pin "a" on the vss to pin a31 on the ecm. The a pins on the ecm are the red connector. john

 

[frostydevil]

Matt, I specifically requested the corvette servo along with the vette torque converter when I had it rebuilt, I can only hope they put it in. IIRC, in the larger B-body, the vette torque converter stalls around 2010 or somethin...It does make a good difference and is fun to drive. I didnt want to go any larger on the stall due to my gears in the rear.
John, thanks man! Thats going to help alot today when I start to do continuity tests. I have a '94 OBD1 system...I hope your manual is for an OBD1....Thanks again!

 

[MrBuick (Magnum)]

94/95 used the same VSS and PCM. In 96, they swapped to the OBD-II PCM, and the VSS that used a different style connector on the other side of the tail shaft housing.

 

[frostydevil]

Update:
right now I have no speedometer, odometer, or trip meter. Transmission doesnt want to shift out of first, but when it does, it lurches into 3rd, and CEL comes on, throwing codes 24 and 83. Before my pcm swap, the codes were 24 and 72. I took it back to the shop that did the rebuild and they tried to fix it by replacing the VSS. It still does the same thing. needless to say, they cant fix it and is beyond their expertise. My EMI fuse is still good and power is present at the contacts. Pcm swap did nothing to fix. I replaced the wiring even, from the VSS to pcm pins a31 and a32. Still no change. Any thoughts? I really dont know where to go from here and I cant just let the car die.... Please help LOL! Is there anything else that would cause this to happen?

Thanks Cory. The yard was full of '96's, but only one '95 I could take from. I was glad it still there. Were ALL '95's OBD1? Or did they switch half way through the year?

 

[MrBuick (Magnum)]

As far as I know, all of the 95 LT1's were OBD-I. I know either the Y-body, or F-body switched to the OBD-II plug in 94-95.

 

[turbostar]

Frosty,have you pulled the VSS yourself and looked at it? It should be easy to pull out without hurting anything.There is a wheel on the trans output shaft that is slotted and as the shaft turns the slots break the magnetic field and gives a signal. In looking at the service manual,it appears that the slotted gear on the output shaft is roughly centered in the hole that the vss fits into. I repaired a manual tranny once(speedo was not working)where the drive gear on the output shaft had moved and would not drive the speedo gear. With the vss removed I would look into that hole(maybe with a mirror)and make sure the slotted gear is where it should be. Also the service manual has a resistance check for the vss-it should read between 1260 and 1540 ohms. Personally I would not suspect the ecm as being the problem. This should not be rocket science for a good tranny shop-if all your checks do not show the problem,then I would talk to another tranny shop. john

 

[turbostar]

Frosty,here's a good check to narrow down the problem: The vss generates a voltage in addition to the pulses per mile. You can check the voltage at the ecm to see if the ecm is getting a signal from the vss. The output voltage from the vss varies from 1/2 volt at 100 rpm to 100 volts at 8000 rpm(I am sure the service manual is refering to output shaft rpm). So either disconnect or tap into the wires to a32 and a31(red connector)and measure the voltage as you drive the car. I am betting you get zero voltage which would tell you that the vss signal is not there.If the ecm does not get a signal from the vss,then the ecm thinks the car is not moving and would not shift. Also if you get no voltage signal then that would be a good indication that the problem is not with the ecm.When you are measuring the voltage remeber that the purple wire(a31) is the ground side. john

 

[frostydevil]

I will definitely try that and check the voltage. John, I have not yet attempted the hairy job of bracing up the tranny to remove the crossmember and my crossover exhaust to access the VSS. This is almost my next step however and I'm not looking forward to it. I am trying to take the shops word for it. They said they checked the fit, to make sure the shaft was in the right spot, even with the new VSS they put in. (however they took it back out because there was no change) If i end up buying a VSS and putting it in, and that fixes the problem, wow am I going to be 'effin pissed!!!

Excellent info guys....Thank you so much for helpin me out with this!

 

[turbostar]

I would do the voltage check first. As I understand the manual,that will tell you where to go next. "IF" you have voltage at the pin,then suspect the ecm(even though I don't think that will be the case),and "IF" you don't get voltage,then you know the vss is not providing a signal. Either way it will tell you where to go next.john

 

[frostydevil]

update:
Theres gotta be a short somewhere.....Where? Who the hell knows. After buying a new bike, the wife had the truck Saturday morning and I needed to go to the hardware store to get some Carb/choke cleaner. It just got done raining and everything was soaked. I jumped in the car, fired it up and took off. Speedometer worked and tranny shifted fine, indicating the VSS is fine. Got it in Monday morning when everything was dry to take it to work and ....same shit. I wonder if power isnt being cut to the tranny? Does anyone know where the power wire that supplies the tranny is, what color? The car has just been sitting cuz I just dont know what to do with it.... (sigh)

 

[turbostar]

What a strange problem. Based on what you are saying about how the car worked correctly in the rain,I would think instead of a short you may have a poor connection/intermittant open.Water conducts electricity so the moisture could have improved a bad connection. If you really believe the rain made a difference,I would perform a little test.Take your garden hose and spray water around the VSS on the transmission and then test drive the car.If it works properly then suspect the wiring/connectors at the vss. Hope this helps.