Mph on scanmaster jumping around

[Pete Revenidis]

My mph on my scanmaster started jumping around this weekend on its first ride after sitting for 2 months noticed torque converter was locking and unlocking in top gear is it the speed sensor in the trans or something else tia
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[Turbotre]

The speed sensor (VSS) is located on the back of the speedometer.If your regular speedometer is operating smooth,then it's probably the data line going to the scanmaster.

 

[earlbrown]

Is your speedo needle bouncing too? If so, it sounds like your cable is shot. Before I replaced mine, it would drive my cruise control berserk on the interstate.

 

[Pete Revenidis]

The speedo was replaced before i bought it to the 140 mph it was 15 mph off from the day i got it. Its not bouncing but the scanmaster was correct before it sat i had checked it with my gps and it was dead on with that being said the tack is also off by 1200rpm on the cluster

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[turbo nasty]

Grease the speedo cables inner cable. the needle may not bouncing alot but the cable can cause the vss to toggle 2-3 mph and if your right at the chips programmed MPH for TCC lock then it will ...for instance...45 mph lock...occilate to 44 or lower...unlock...back to 46...lock.

 

[Pete Revenidis]

The problem is the scanmaster speed will jump around 20 30 mph it will read 31mph than jump to 60 than back down to 19 and so on

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[earlbrown]

It's probably because the scanmaster reads the ECM every 1.4 seconds. With a speedo cable jumping around the reading will vary depending on whether the VSS is getting hit with a rebound or a bind from the cable.