No speedometer

Discussion in 'Engine Performance + Maintenance' started by Dennis Wilkie, Jul 21, 2019.

Car Parts
  1. Dennis Wilkie

    Dennis Wilkie Newbie

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    In my 92 4x4 k1500 my speedometer goes straight to 90 mph after I let off the brake, and it will constantly jump while i'm driving. The rpm guage also rarely has a slight jump to it, and the gas guage is off by about ½ a tank. But I hove NO REAR BRAKE SYSTEM in this truck, period...NONE. I've been trying to figure out this speedo issue since January and have had no luck. Anybody know anything about this or had any luck fixing similar problems?
     
  2. DerekTheGreat

    DerekTheGreat I'm Awesome

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    The tach jump sounds ignition related, so failing or damaged insulation, plug boots, cracked plug, ignition control module..

    Other stuff could be wiring related, perhaps the speedometer is shorting out or the cluster itself is bad. The fuel gauge in my '89 didn't work reliably and neither did the temp gauge but swapping it out with a known good one fixed those issues. If that doesn't change anything, a wiring diagram would be useful with trying to figure out why the brake light circuit is affecting the speedometer.
     
  3. Dennis Wilkie

    Dennis Wilkie Newbie

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    Well, my multimeter says it's only getting .03 volts to the VSS connector, so it looks like i'm going to get to trace down some wiring...yay
     
  4. Dennis Wilkie

    Dennis Wilkie Newbie

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    So, I traced the green and purple wires from the vss connector and they look good all the way back up to the cluster. Could it be the vssb/drac? Awhile back, I had my dad unplug it while I was driving and it had no effect on anything noticeable. I pretty much destroyed my dash following the wires, because it was as brittle as a potato chip. But if the wires look good, and the vss has no power reaching it, there's only 3 things I can think of that it could be...the ecm, the vssb, or the cluster itself, none of which are a cheap fix. I really don't want to cut into the wires in between each part to get a voltage reading, but i'm running out of ideas.

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