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Discussion Starter #1
Every once in awhile I'll start my car and put it into reverse and I'll just barely be moving and the speedo will completely peg to the other side of it. It doesn't happen all the time just once in awhile.

Also when I cruise at exactly 30 mph my tranny will kick in and out of lockup until i go 1 mph faster than 30, or drop below where it won't be locked up. Is that normal???
 

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sounds like your vss (vehicle speed sensor) could be on its way out

either that or some other subtle wiring issue. could be a shoddy ground (but so much stuff runs off the same ground, you'd figure you would have other symptoms..)

that lockup behavior isnt normal by any means

your ecm is probably confused because of the inconsistent speed signals. it should stay put, until you give it a reasonable amount of throttle to break it out of lockup.

datalogging would be the best way to diagnose a sketchy VSS
 

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i totally forgot to make my main point, and that's that the speedo is slow to respond to changes in speed, but the ECM isnt.

a crappy signal might not show up, the speedo will smooth it out, but your ecm could be going nuts trying to figure out how fast your car is going
 

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Discussion Starter #4
I had a hunch that it could be VSS related, my only issue is that I have a 96 with OBDII so datalogging is a spendy option correct? Can I drive around with my scanner and monitor the speed and see if it jumps around? I'll have to see if my scanner even has the ability to ready the VSS.
 

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yeah i think it's a bit spendy; monitoring the values without logging them so you can view them on a graph for smoothness, i doubt you'll catch it

handheld scanners dont seem to have a high enough sample rate
 

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Discussion Starter #6
That makes sense to me, you'll probably never catch something like that on a handheld scanner. Looks like software so i can datalog is north of $400, Ouch!! I guess for now I'll maybe try replacing the VSS and look over the wiring and check for any breaks.
 

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There is a free obd2 scan program by Gary Doug, posted by me, in the 4th gen section. It will require an elm327 cable to work with your laptop. They are available on ebay and amazon.
 

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Discussion Starter #8
I'll check that out and see what I can do as far as getting a cable and all. I'll have to try and borrow a laptop cause I don't have one at the moment.
 
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