Like (apparently) most of you out there I have had many problems with my cruise control. All the usual suspects and one new one. Over the years, I replaced all the vacuum lines (cracked), realigned the switch on the brake pedal so it works properly. I used procedures (which I think I found here under articles) to test the ECM with a multimeter.
In my latest effort, I determined that the vacuum pump was not working. I have been unable to find testing procedures for it and the limited information I was able to find on it indicated that it is non serviceable and must be replaced if it fails to work.
Here's how I learned to test the pump, diagnose and fix the problem.
1. Figure out the control scheme:
After removing the pump from the vehicle, Look at the pump and notice the three spade connector. One lead takes power. The remaining two go to ground (one to energize the dump valve (shut) and one to run the pump motor.
As you can see in the photo, I have attached three test leads to my pump along with a vacuum gauge (gauge is flashed out in the photo): red, green and black. If you attach your test leads the same way I did, you can CLIP the black one to battery positive. I clipped mine to the hot lug on the alternator.
Now TOUCH (don't clip) the green wire to ground. Touch and release a few times -- if the dump valve solenoid is working you can hear an audible click. If you hear this click, that's probably a good sign.
Now CLIP that same green lead to ground to hold the solenoid closed. Either have your vacuum gauge attached or just hook it up directly to the actuator (the actuator is kind of a bad idea to use if you haven't already tested and ensured it and its associated tubing are free of defect). If you go the vacuum gauge route, note that this little puppy builds vacuum fast. Now TOUCH the red lead to ground a few times. The motor will run and if you are attached to a vacuum gauge you'll see the vacuum build up; if you're attached to the actuator, you'll see the little bag suck in and the throttle actuate. When the red lead is removed, the motor will shut off and the vacuum should hold.
When you unclip the green lead from ground, the dump valve will open and the vacuum will be released.
If your tests don't work as expected, your pump is probably broken. There are two covers on the pump that you can remove to figure out what's wrong.
The cylindrical cover to the right of the leads in the picture covers the motor. If your motor doesn't run, perhaps pull that one off (that's right pull it off, no need to twist or anything). This will expose the motor. If the motor doesn't run and it's all corroded when you pull the cover off, the reason for it not working will be obvious. Otherwise, there isn't much to do under that cover except be able to rotate the motor shaft to see if it's seized or not.
The lower cover is much more interesting it's on the bottom of the motor it's flat, oval shaped, has a gasket around it and says HELLA on it. You can carefully pry it off with a flat blade screwdriver. You'll see the dump valve solenoid and some wires along with the mechanicals of the pump. You're on your own fixing what you can under that one. My solenoid was seized because apparently water had seeped into the unit at some time. A little patience, some silicone spray and I worked it loose. I reassembled the pump, tested it, reinstalled it in the Disco.
Once again, I have cruise control!
In my latest effort, I determined that the vacuum pump was not working. I have been unable to find testing procedures for it and the limited information I was able to find on it indicated that it is non serviceable and must be replaced if it fails to work.
Here's how I learned to test the pump, diagnose and fix the problem.
1. Figure out the control scheme:
After removing the pump from the vehicle, Look at the pump and notice the three spade connector. One lead takes power. The remaining two go to ground (one to energize the dump valve (shut) and one to run the pump motor.
As you can see in the photo, I have attached three test leads to my pump along with a vacuum gauge (gauge is flashed out in the photo): red, green and black. If you attach your test leads the same way I did, you can CLIP the black one to battery positive. I clipped mine to the hot lug on the alternator.
Now TOUCH (don't clip) the green wire to ground. Touch and release a few times -- if the dump valve solenoid is working you can hear an audible click. If you hear this click, that's probably a good sign.
Now CLIP that same green lead to ground to hold the solenoid closed. Either have your vacuum gauge attached or just hook it up directly to the actuator (the actuator is kind of a bad idea to use if you haven't already tested and ensured it and its associated tubing are free of defect). If you go the vacuum gauge route, note that this little puppy builds vacuum fast. Now TOUCH the red lead to ground a few times. The motor will run and if you are attached to a vacuum gauge you'll see the vacuum build up; if you're attached to the actuator, you'll see the little bag suck in and the throttle actuate. When the red lead is removed, the motor will shut off and the vacuum should hold.
When you unclip the green lead from ground, the dump valve will open and the vacuum will be released.
If your tests don't work as expected, your pump is probably broken. There are two covers on the pump that you can remove to figure out what's wrong.
The cylindrical cover to the right of the leads in the picture covers the motor. If your motor doesn't run, perhaps pull that one off (that's right pull it off, no need to twist or anything). This will expose the motor. If the motor doesn't run and it's all corroded when you pull the cover off, the reason for it not working will be obvious. Otherwise, there isn't much to do under that cover except be able to rotate the motor shaft to see if it's seized or not.
The lower cover is much more interesting it's on the bottom of the motor it's flat, oval shaped, has a gasket around it and says HELLA on it. You can carefully pry it off with a flat blade screwdriver. You'll see the dump valve solenoid and some wires along with the mechanicals of the pump. You're on your own fixing what you can under that one. My solenoid was seized because apparently water had seeped into the unit at some time. A little patience, some silicone spray and I worked it loose. I reassembled the pump, tested it, reinstalled it in the Disco.
Once again, I have cruise control!
