I think it's the vacuum pump, but I want to make sure before I buy another. The cheapest one I can find is at a salvage yard for $55. My vacuum pump was loud before, and cycled off and on a lot. It doesn't sound or feel like it's running at all anymore. But I can use cruise on flat ground and even a little bit of uphill. But as soon as I go up a hill it kicks out and will not come back on. I even pulled over the other day and shut my truck off and when I started driving again it still didn't work. But if you park it for awhile it will work again until you start up a hill. Any help would be greatly appreciated. Thanks.

 

The speed control system is fully electronically controlled by the Powertrain Control Module (PCM). If equipped with a diesel engine, electronic control of the speed control system is integrated into the Engine Control Module (ECM). A cable and a vacuum controlled servo are not used. This is a servo-less system. The controls consist of two steering wheel mounted switches. The switches are labeled: ON/OFF, RES/ACCEL, SET, COAST, and CANCEL.

 

I have a 4.5 and have the same issue, but have not looked at it to find a correct fix. There is a vacuum pump behind the pass battery and a cruise control pod under the drivers side battery. I am leaning toward the cruise control pod myself but that is just a swag. Good luck and post if you get it fixed.

 

Mine was doing it too. I changed the brake light switch, and it fixed it.

 

may not be revalent but, my other truck a gasser 05 Z71 the cruis would work on and off you never knew when it world just quit, it too was the brake switch,

Oh...the dealer wanted 72.00 bucks for it, but the local repair shop did it for 50.00 bucks installed, a DIY 1/2 that.

 

First try holding your foot under the brake pedal and pulling UP to see if this fixes ot.The brake switch is non adjustable but the bracket that holds it can be adjusted by the old GRUNT method.

 

I have tried pulling up on the brake when driving, no luck. The cruise works fine on a flat road. When you hit a bridge or hill it will just drop out and not work. The cruise light is on and it will take a shut down/restart to clear out the issue. Then good until it tries to apply gas to go up a small hill. High Idle works fine. The first time it did it was on a hunting trip, I had been driving about 30 miles on the way home and it justed dropped out. I used it that morning on a 120 mile trip there with no issues.

 

I tried that a few days ago after someone told me that it might be the brake light switch, and it stayed on. I think Napa has them for less then $20, but not sure yet.

So if my vacuum pump quit working what is it used for? I don't notice anything else wrong with my truck. It was really loud before and you could feel it running, it cycled on and off every minute or so. Now I can't hear it or feel it running. What does the vacuum system do for these trucks? Thanks.

 

It appears from the service manual that manual trans trucks don't use a vacuum motor/servo combo.....however automatic trucks do...page 684 (8P-3) of the service manual has the info you need.

 

Yes sir, that did the trick. I just got under the dash, pushed the brake light switch button in a couple of times and gave it couple of twist. I did not move the braket at all. It seems to be working now. Thanks for the info.