1988 F-250 4x4 Diesel Cruise Control Temperature Sensitivity Weirdness

[rempfer]

My truck's cruise control works perfectly in colder weather.

But once the truck's warmed up if the weather also warms to the mid-60's or above the cruise control will disengage and no amount of massaging the control buttons can coax it into working again.

Quite predictably though, if the ambient air temperature cools to (or falls below) 60 degrees F the cruise control will work (start working again) absolutely reliably.

Any idea what might be the culprit here? Thanks!

 

[Thewespaul]

I would hook up a vacuum gauge to the back of the vacuum pump and verify you have good readings there, very possible your pump is fatigued and can’t perform in the heat

 

[gandalf]

I've just sent off the diagnostic for the older, vacuum actuated, cruise control. I hope it's what you need, that it helps you solve the problem.

 

[79jasper]

Well the switch reading do work off of a resistance value. So could be something in the wiring, clock spring, or buttons.
But checking the vacuum is a good start.

Sent from my SM-G892A using Tapatalk

 

[Sidewinded_idi]

Check the adjustment on your vacuume pedal switch. On mine if it was backed out just too far it wouldn’t engage.