This guide is being written around the ford F series light and medium duty trucks that are equipped with 6.0 and 7.3 liter turbo diesel engines or a caterpillar diesel engine (typically found in F650-F750 trucks). Other vehicles may be similar but please consult a repair manual for your application.
For this diagnosis/repair you will need:
A multimeter.
Ratchet and 10mm socket.
Long needle nose pliers.
Symptoms of a failed electrical vacuum pump in this case can include the climate control only working on defrost (this is a factory default safety system) and auto four wheel drive not working.
Step one: Find the leak.
Ford trucks equipped with diesel engines have two vacuum pumps. One is engine mounted and this is what provides vacuum for your brake assist. We are NOT dealing with this one here. What we are dealing with is an electric vacuum pump, mounted near the blower motor, that supplies vacuum for the dashboard climate controls and the four wheel drive system (if you have auto locking hubs). You will need to inspect the vacuum lines to make sure they did not come apart at some point. Fix any leaks you find.
Step two: Found a leak? Fixed it? Test your repair.
Start the engine and let it run for about 30 seconds so that the pump can build vacuum. You should go ahead and check to see if the blower can work anywhere else in the system. (Remember, defrost is the factory default.) You should also check your automatic four wheel drive hub engagement (if equipped.) Does it work now? If so, you are finished. If not...
Step three: Test the vacuum pump and connection.
If fixing the leak did not help, you need to take your multi meter and test the connection and the pump itself. The pump will be on the passenger side of the vehicle, near the blower fan. It will have a two pin pigtail connected to it. Disconnect the pig tail and turn the key on without starting the vehicle. Place one lead on to each side of the plug (it does not matter which one goes where just so that the leads are contacting the metal in the pigtail. If you get a reading, move on to the pump itself. If there is no power, you need to check the fuses and perform the test again.
If there is voltage, set the meter to check continuity, and touch one lead to each pin at the connection in the motor. You should have continuity which, in most cases, will make the meter beep. This motor is getting power whenever the key is turned, so if there is no beep, the motor has failed.
Step Four: Replace the motor.
Using a 10mm socket and ratchet, remove the two screws that hold the bracket for the vacuum pump onto the inner fender. You can now remove the pump and bracket from the vehicle. The pump is mounted to the bracket with three rubber shock absorber mounts. Pulling on the pump itself should free it from the bracket.
If the new pump comes with replacement shock absorbers, remove the old ones and install the new ones, using the needle nose pliers to pull them through. Place the pump on the bracket over the shock absorbers and use the pliers again to pull the shock absorbers through the pump mounting holes. Installation is the reverse of normal.
It was my experience last week, when I replaced three of these in a day, that the pump itself went bad in two of the cases. in one case, vacuum lines had become disconnected, which caused the pump to burn out.
Sorry, no pictures this time.
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