VSS and Speedometer

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Supercharged111

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Could be the cluster, the PCM supplies both RPM and speed to the cluster. That said, the speedo output is separate from what it calculates actual vehicle speed to be from VSS input. So with that said, if your cluster is shot but it's consistent it can be fixed with a reflash. . . at least at one speed. If its wrongness trends differently at different speeds you're still screwed. With EFILive, you can opt for whether or not you want trans shift speeds to change with the speedo updates.
 

Donald Mitchell

1990 C1500 5.7L
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Could be the cluster, the PCM supplies both RPM and speed to the cluster. That said, the speedo output is separate from what it calculates actual vehicle speed to be from VSS input. So with that said, if your cluster is shot but it's consistent it can be fixed with a reflash. . . at least at one speed. If its wrongness trends differently at different speeds you're still screwed. With EFILive, you can opt for whether or not you want trans shift speeds to change with the speedo updates.
Are you sure your GPS is set to mph not kph?
 

PewterK1500

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The gps is in mph, scan tool is in mph. I’ll find a cluster at a junkyard take it down the road and give an update as soon as I can.
 

PewterK1500

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Sorry for the late update. It’s been cold and I don’t have a garage yet. I put the new junkyard instrument cluster in and it’s spot on. Must’ve got lucky to find a good one on the first try. I ran the live scan tool for the vss and the gps speedometer app ran the truck up to 65 mph and everything matches up. Swapped over the odometer from the old cluster too! Thanks for the help and the replies!
 
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