Cruise control loses speed.

[chris142]

Took a trip today. Everything was fine. Stopped 100 miles from home for lunch. Got back in the truck and the cruise would not set. I eventually got it to work but.... I set it @ say 70mph...with within a few minutes it starts to lose speed even down hill. I can press on the go pedal and bring it back up only to have it lose speed again. Where do I start?

I have no idea how this system works other than vacuum from the vacuum pump must pull a diaphragm inside the cruise controller thing.

 

[david85]

Power brakes still work ok? if not, I would be looking for a vacuum leak. If that checks out...

Pull the air cleaner assembly off and have a look at the throttle cable bracket. There should be two cables there; one for the pedal, the other for the cruise control servo. The cable for the cruise control can sometimes pop out of the bracket. Mine is held in place with a zip-tie.

 

[chris142]

I think I found it! There is a vacuum can,looks like a coffee can. It has a hole rubbed in it. A vacuum hose has good vacuum going into it but nothing coming out of the hose that feeds the cruise control thingy. I blew into the coffee can and found the leak. I will solder it up tomorrow. I am convinced that the leak won't let the cc thingy pull on the cable.

May not even need that can because we always have vacuum from the vacuum pump. Unlike a gasser that loses vacuum when you open the throttle.

Brakes worked fine all day. Guess that can had enough and decided to leak after lunch LoL.

 

[david85]

Been a few years since I took my coffee can out. They all rust eventually.

 

[chris142]

Been a few years since I took my coffee can out. They all rust eventually.

Does it work ok without the can? Rust is not a problem here in the desert. Mine rubbed against something.

 

[david85]

Honestly, its been so long since it rusted out I can't remember if it made any difference. I'm sure ford put it in there for a reason, but it seem to work fine without it. Maybe better response time when you hit the accel or resume buttons?

 

[Knuckledragger]

The vacuum pump does not have a large capacity, the coffee can is probably acting like an accumulator, storing enough vacuum to do the job. Fix the can and you should have good cruise control again.