speedometer pegged at idle
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5th Wheeling
Joined: Aug 2017
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speedometer pegged at idle
'94 F-150 (302) 4x4: The other day when I was driving, the speedometer pegged all the way to 80 and transmission started shifting hard. I pulled over and pondered for a bit, then start driving again slowly down the road to make it home. Eventually after a few minutes, the speedometer went back to normal and everything drove fine. Any ideas?
There is another intermittent issue I'll mention in case it's related: Periodically when you put the key in and turn it everything goes bone dead, like a dead battery (battery is new and tests fine). If you then take the key out and jiggle the shifter a little bit and put key back in and turn it, it usually is fine and starts right up. I don't think it's a neutral safety switch issue, since that wouldn't normally cause the electrical system to just go totally dead.
I did rebuild this transmission (4r70w) about a year ago, but it's been fine ever since.
There is another intermittent issue I'll mention in case it's related: Periodically when you put the key in and turn it everything goes bone dead, like a dead battery (battery is new and tests fine). If you then take the key out and jiggle the shifter a little bit and put key back in and turn it, it usually is fine and starts right up. I don't think it's a neutral safety switch issue, since that wouldn't normally cause the electrical system to just go totally dead.
I did rebuild this transmission (4r70w) about a year ago, but it's been fine ever since.
Fleet Owner
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From: Easton,Ks
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5th Wheeling
Joined: Aug 2017
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Thanks guys. The ignition switch having a grounding issue makes sense for the dead start scenario. The speedo being pegged is a wierd one though. Shifting was definitely affected which sounds like VSS. But, there seems to be agreement that isn't it.
Any suggestions on where to hook up my multimeter when it happens next to troubleshoot?
Any suggestions on where to hook up my multimeter when it happens next to troubleshoot?
Elder User
Joined: Sep 2018
Posts: 735
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From: NC
If the ignition is having circuit problems that makes sense for the speedo to flop over to the right and not go back, as my truck when the key is twisted it goes all the way to the right then goes back to zero, it is part of the self calibration design from what I recall reading about it.
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Fleet Owner
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From: Easton,Ks
The VSS has no moving parts with no power going to it.
It generates a small AC signal.
The only way it goes bad is that its magnet might lose some flux generating ability and may generate very little AC voltage.
Or of course it can get broken also.
If the wiring to it gets shorted together the there would be zero voltage and the speedometer would read zero.
You may have a bad PSOM but that would be about it.
More that likely you either lost a ground or the power to dash.
It may be the Ignition switch or its plug but can not see how it would do all of the things you said.
It generates a small AC signal.
The only way it goes bad is that its magnet might lose some flux generating ability and may generate very little AC voltage.
Or of course it can get broken also.
If the wiring to it gets shorted together the there would be zero voltage and the speedometer would read zero.
You may have a bad PSOM but that would be about it.
More that likely you either lost a ground or the power to dash.
It may be the Ignition switch or its plug but can not see how it would do all of the things you said.
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