Cruise control cuts itself off

[EMD_DRIVER]

I was told that the cruise control in my truck would cut itself off and have had it happen several times.

It happens under load and gives no warning at all..

Is there a way to prevent it from happening? For that matter, are there ANY adjustments that can be made to it?

Gary

 

[Agnem]

At what speed? Under 45 or 40 I forget which. It will cut out. That's by design.

 

[EMD_DRIVER]

I've had it cut off at 60 before, so I'm not sure about that. What senses the vehicle's speed on an 87?

Gary

 

[69oiler]

it will cut out if you lose too much speed, say over 5 mph loss. i dunno why but i have had a bunch of vehicles do this.

cruise should work as low as 25-30 mph but if your truck cant maintain the speed the cruise will cut out.

 

[LCAM-01XA]

What Rob said - as you lose speed (usually due to an uphill) it will keep increasing the throttle, at some point truck will downshift and pretty much go WOT, if you're still losing speed and end up going 5mph or so lower than the speed you set the cruise at the thing will shut off on you, as there really ain't nothing more it can do to maintain the desired speed, and cause something obviously ain't right with the whole situation to begin with.

 

[EMD_DRIVER]

I probably wouldn't have this problem, if I had a turbo on it... Oh well..

6.9 + C6 = Slow poke

Gary

 

[Agnem]

Get that pyro yet? Your cruise control could be full throttling your engine. Not good with WMO and no pryo.

 

[EMD_DRIVER]

Still working on that one Mel...

 

[david85]

My 1986 trucks will drop 15 KPH before they will shut down the cruise (about 9 MPH).

They will also work down to about 35 MPH I think.

Wonder if the break light circuit could be causing this. There is also a weird magnetic switch that is used to disengage the cruise control via the brake signal.

This is the factory service manual for the 1985 model year cruise system, but the system changed very little over the 1980-1996 era. Lots of diagnostic and theory of operation in there:

http://www.garagenet.biz/cruise.pdf

Hope it helps.

 

[69oiler]

I probably wouldn't have this problem, if I had a turbo on it... Oh well..

6.9 + C6 = Slow poke

Gary

if it makes you feel any better my 6.9 NA with the 4 speed manual did it too. a turbo would help.