How to Test a Fuel Pump on a 1999 Dodge Truck
- 1). Turn the ignition key on and listen for the familiar hum of the fuel pump. If it can't be heard, open the fuel filler cap and listen for the pump to come on as the helper turns the key on. Remove the cap on the Schraeder valve on the fuel rail that feeds the fuel injectors. Thread the fuel pressure tester hose onto this fitting.
- 2). Turn the ignition key on and observe the fuel pressure. It may be necessary to cycle the key two or three times to build the pressure. It should register 49 pounds of pressure if it is working properly.
- 3). Check the fuel pump fuse and the relay for operation if the pressure in the previous step was 49 pounds of pressure or if there was no pressure. Use the voltmeter and check across the fuse for 12 volts. Replace the fuse if blown. Pull the relay and check for 12 volts at one terminal with the key off. Turn the key on and check for a second terminal to have power. If there is no power to the second terminal when the key is turned on, there is a wiring problem between the computer and the relay.
To check the pump for operation, put the voltmeter on ohms and check the other two terminals that did not have power for a ground. Once the ground is located, jump the terminal that had power with the key off and the last terminal that was not to ground or had power. This terminal is to the fuel pump. Jumping these two terminals will turn the pump on if it is operating properly. Check to see if the pump operates and the fuel pressure it produces. If the pump works, replace the relay. If the pump fails to operate, the pump is defective. - 4). Check the pump for volume. Remove the Schraeder valve core from the fuel rail and use a piece of hose that fits securely over the threaded end of the Schraeder and the other end into a glass container. Cycle the key on and off two times allowing 5-second intervals between cycling. Watch the glass container for amount of fuel flow and volume. The glass should contain 3 to 5 ounces of fuel. If very little fuel is evident, the fuel pump is defective.
