my buddies budget camaro has a problem and im,,, at a loss.

the car has a service engine soon light that comes on and goes off without any pattern or method. probing the computer a week or so ago we found that the car had not only a bad oxygen sensor but a bad MAP and a supposedly bad vss as well.
we replaced the MAP sensor and reset the computer, drove it a lil and now it doesnt bring up the MAP code, or the vss code....
the speedometer sometimes works sometimes doesnt but the times dont coincide with the SES light which we arent even sure if it works right since its been on so much,. could it be a loose wire behind the speedometer? and the fact that it keeps fluctuating makes the computer think the vss is bad? or maybe a bad speedo? blah... help is appreciatted

 

The ECM won't instantly throw a VSS code. You would think it would come on instantly when the speedo drops to zero, but it doesn't. The ECM has to be damned good and sure that it's bad before it throws a check engine light for the VSS.

If the VSS is good, a loose wire is unlikely. Most often the speedo in the gague cluster itself is bad if it sometimes just drops to zero MPH. I went through this recently with a 91 GMC Jimmy. No codes, but the speedo would suddenly be at zero. After replacing the VSS and the ECM there was nothing left but wiring and the gague cluster itself. I took a shot in the dark. $225 later for a factory-rebuilt gague cluster and I have a working speedo again.

p.s.- replace that O2 sensor on general principle. Unless you KNOW it's good, assume it's bad. You can buy an O2 sensor socket from any parts store for about $8 to get it out (soak the O2 liberally with penetrating oil for at least a few hours before attenpting removal if it's the factory original- they're usually almost WELDED in after being installed in the exhaust manifold for a decade or more).

 

check the park neutral switch. i thinkt he ecm uses it as a check for the vss. if the vss was reading say 60mph and the p/n switch was closed, then it might think the vss is bad. try to find a chart of how all the different sensors are inter-related because im not sure how exactly it is setup on these cars.

 

sorry it took so long to reply....
allright,, well, in the meantime since my last post (thanks for the suggestions guys) we've fixed the 02 sensor replaced the fuel pump and doen a partial tune up on the ignition system which together with the map sensor has almost doubled his gas mileage. we have also replaced the guage cluster completely and it continues to twitch,, so im going with loose wire,, now, thank *** that wiring harnesses are bundled so tight that i can probably rule out everything except for the connection to the vss and the computer, and the connection from the comp to the speedo,, which is probably allright unless we have car mice,,ehhh....
so my questions are,,, where is the vss actually,, is it the black box under the console or is it actualy on the trannie? also,, what are the wire colors and how many,,, and can the computer lock up the converter in his car without the vss signal?

on a side note,,, got my heritage car out today to stretch its legs a lil,, haha who says the 305's have no power? got up to fifty five in less then,,, ohh about 100 feet, might not be a high speed but when you're going uphill towards your house with your a** in the rear seat its enough to scare the sh*t out of you ( and your girlfreind ) lol,,,also didnt realize that my cars been taking off in second gear for no good reason,, drop it in first and gun it and it starts to look like *** was playing with crayolas on your driveway.
thanks for the help guys..

 

In the '91 the VSS is in the tail shaft housing of the transmission. Odd looking thing with a two wire connector going into it. On drivers side. The two wires go to the ECM which buffers the signal.

The ECM sends out two signals (as pulse streams), one to the speedometer and the other to the cruise control.

RBob.

 

thanks man. how much is a vss? and is it hard,, or simple to change,, it sounds fairly simple once we get it on the lift,, might just change the thing while its puking the trans fluid out...

 

Don't know what they cost. Easy to change. A single bolt that holds a small strap clamp in place. Remove that and pull the VSS straight out. Change the gear (pulls off) to the new one and installation is opposite of removal.

RBob.

 

Cost depends on which version you have. their are about 3-4 different vss' used in 91. Cost ranged from 25-105.

I highly suggest pulling the one you have, and taking with you. Keep the little plastic gear at home. (plastic gear may be all thats bad).

It will either take a 10mm wrench, or 13mm wrench IIRC.

It will leak tranny fluid while its out, get some while at parts store.

 

thanks alott guys,,,, i think this will take are of it but if its still not working after we change this thing im going to start getting worried.. not going hunting for a loose wire past the ecm..
thanks alott for the help guys,, huge time saver