Cruise Control ?'s
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Mountain Pass
Joined: Feb 2004
Posts: 197
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From: In the swamps of Florida
Cruise Control ?'s
Hello all, I just got the cruise control working on my '86 F-150, but I still have a bit of a problem. All the functions work properly, but the truck will not hold a steady speed. It will accelerate 2-3 mph above the set speed and then decelerate to about 2-3 mph below the set speed. The cycle just continues, regardless of the flatness of the road. I guess my question would be where to start? VSS or CC module? Thanks for the help.
Senior User
Joined: Aug 2006
Posts: 113
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From: Texas
My 86 250 started doing that and I noticed that the speedometer was bouncing a lot. It would bounce, for example, from 55 to 65, in a regular pattern. Every time it bounced the cruise would readjust and speed up and slow down, just as the speedometer did. The speedometer soon stopped working, as did the cruise control. You probably need to pull the cable and lub it with graphite, or replace the whole cable.
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Joined: Jan 2001
Posts: 56,977
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From: Virginia
To tight or too loose can cause this. The servo or diaphragm(whichever you have) needs to be somewhere in the middle of it's mechanical travel when it's working. If it's too tight, then it pulls just a little bit to achieve the set speed, but when it relaxes, it runs out of travel. Of course if it's too loose, it will pull all of it's travel to achieve the set speed. Also you may have some check valves and a vacuum tank in the system too, which smooths out the vacuum from the engine.
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