When the transmission is in park the speedometer goes up fast

Tiny
TREVORMCCASLIN
  • MEMBER
  • 1987 PONTIAC FIREBIRD
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 167,000 MILES
Okay, when my car is in park I rev the engine and the speedometer goes up and it goes up fast I can get to the max speed just by revving the car. Any idea what this would be?
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Saturday, October 17th, 2020 AT 7:47 PM

9 Replies

Tiny
KASEKENNY1
  • EXPERT
What I suspect what is happening if the speedometer is moving in park is there is an issue in the cluster. Did you just purchase this vehicle or did this issue just start? Does the speedometer work properly when driving?

This vehicle has a driven cable for the speedometer that is run off the tail shaft of the transmission. So if the vehicle is not moving this gear should not be moving.

I would disconnect the cable and then retest to see if it still moves. Can you get a video of this as well?
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Sunday, October 18th, 2020 AT 7:25 AM
Tiny
TREVORMCCASLIN
  • MEMBER
This is all electric. I just recently bought the car and the wires where cut somewhere I could not find them, so I went to the buffer bot and ran new wires and bought the plugs for the speed sensor on the back of the transmission so the speedometer was never working. When I rewired it I can get my car to 80 mph in park just by revving the engine and when I put it in drive and tap on the gas it climes really fast.
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Monday, October 19th, 2020 AT 4:12 PM
Tiny
KASEKENNY1
  • EXPERT
So this is a direct feed from the speed sensor through the gauge and direct to ground. Did you run a new ground wire or at least check to make sure it is a good ground? Then we need to monitor the voltage on that wire when in park and you are reving the engine. If you have voltage spikes then I would think the speed sensor is the issue. If not then the cluster must be the issue.
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Tuesday, October 20th, 2020 AT 8:14 PM
Tiny
TREVORMCCASLIN
  • MEMBER
This car has a buffer box and it goes from the buffer box to the cluster dash the speed sensor wires got cut somewhere by the last owner and when I rewired it not it does this before I had nothing because it was not wired. I was thinking maybe the speed sensor is going bad or the buffer box is acting up.
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Tuesday, October 20th, 2020 AT 8:48 PM
Tiny
KASEKENNY1
  • EXPERT
Okay. Clearly the wiring diagrams are not matching your vehicle so based on that information, I would think the buffer box is the issue and not the speed sensor. Assume this is the speed sensor that they are showing as your vehicle having, it is a driven gear. So if that is not spinning then there is no voltage generated. The box however, could have a short causing the issue.
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Wednesday, October 21st, 2020 AT 6:49 PM
Tiny
TREVORMCCASLIN
  • MEMBER
Possibly a short, but I don t think to because it moves just fine it does not glitch out and all the speed sensor is it s a box basically it does not have any gears on it or anything. I have a new sensor for it but I don t have the car currently because it had a blown head gasket.
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Wednesday, October 21st, 2020 AT 8:39 PM
Tiny
KASEKENNY1
  • EXPERT
Okay. Can you get a picture of the speed sensor and post it? Does the vehicle have a tachometer?
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Thursday, October 22nd, 2020 AT 12:37 PM
Tiny
TREVORMCCASLIN
  • MEMBER
When I get the car back yes I ll send a video and everything.
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Thursday, October 22nd, 2020 AT 6:20 PM
Tiny
KASEKENNY1
  • EXPERT
Awesome. Thanks. We will wait to hear back.
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Friday, October 23rd, 2020 AT 6:33 PM

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