How to Prime a Diesel Injector Pump

by Natalie Lyda
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wrench image by Stanisa Martinovic from

Injection pumps play an integral role in the operation of diesel-powered vehicles. The part allows diesel cars and trucks to run by delivering an exact amount of fuel, under very high pressure, to each injector at a specified time interval. As the fuel is delivered from the injection pump, each injector disburses the fuel into the motor's cylinders, where it combusts, and keeps the motor running. During routine maintenance, such as fuel filter replacements, you may need to prime the injection pump to remove air from the fuel system.

Step 1

Loosen the nuts connecting the injectors to the motor head. This will allow any air between the injection pump and injectors to exit the system during priming.

Step 2

Insert the key into the ignition. Turn the key to the "on" position and turn it slightly toward the "start" position to bump the starter. Release the key after approximately one to two seconds so that it returns to the "on" position.

Step 3

Listen for the vehicle's electric lift pump to begin transferring diesel from the fuel tank to the fuel filter housing and, in turn, the injector pump. The lift pump will sound like a buzzing coming from the fuel tank. If you do not hear the lift pump working, bump the engine a second time.

Step 4

Work with a partner to watch for fuel coming from the injector lines where you previously loosened the connection nuts. Re-tighten the nuts when fuel begins to flow out of the injector lines. At this time, your injector pump is primed with fuel.

Step 5

With the injector lines re-connected to the head, crank the vehicle and allow it to begin running.

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