Speedometer and power drops

1986 FORD E-SERIES VAN
165,000 MILES • V8 • 2WD • AUTOMATIC
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LINDA WAHL
  • MEMBER
  • 1 POST
when I hit a bump the speedometer will drop and even though the engine runs smoothly the power drops for a second before coming back and the speedometer goes up again.
The cruise control does not work. That seems to have something to do with it. I figured it was a loose wire somewhere so I would stop every now and then along the road and send my teenage boys out to just push together whatever wires they could see and that worked for a couple years. A mechanic happened to visit a few years ago and I remember him saying it looked like the wire had hit something underneath and the wires were pulled slightly from the plug. He fixed it borrowing a soldering gun. It worked fine for the last four years but we have lived by the ocean the past several years and I figure that that has now corroded those same wires again, but I do not know what they were. The boys are grown and gone and do not remember and the mechanic is also gone.
Jul 18, 2017 at 8:31 PM
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HARRY P
  • CAR REPAIR CONTRIBUTOR
  • 2,292 POSTS
As far as the speedometer issue goes, check your battery terminals and cables. A weak battery connection can cause funny things like that to happen. My 2002 Blazer starting doing that a few weeks ago. It needed a new battery terminal. Changed it out and it was good to go after that. Check this guide out:

https://www.2carpros.com/articles/everything-goes-dead-when-engine-is-cranked

As far as the cruise control goes, that system is driven by a vacuum actuator. Meaning that the system has to have vacuum pressure to work. After a few years of daily driving, vacuum lines start collapsing when under pressure or just plain leaking. I would suggest taking a close look at the vacuum lines. Check this guide out:
https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

So check into those things and let us know. Good luck!
Jul 18, 2017 at 8:47 PM
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