How to Adjust a Detroit Fuel Injector

by Jeff Woodward
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Fuel injectors are part of the Detroit Diesel fuel system. Fuel is drawn from the fuel tanks by the fuel pump. After the fuel leaves the fuel pump it is sent to the fuel filter. After passing through the fuel filter the fuel is then sent to the fuel injectors. Since injectors are constantly in motion spraying fuel into the cylinders during the intake cycle of the engine, they will eventually fail during the lifetime of the engine. After replacing failed injectors they will need to be set to the correct calibration.

Setting Detroit Diesel Injectors

Step 1

Insert the 3/4-inch breaker bar into the square drive hole at the center of the engine crankshaft pulley. A 3/4-inch ratchet may be substituted for the breaker bar.

Step 2

Push down on the breaker bar to rotate the engine. Observe the cylinders and note when the first injector rocker arm begins to depress on one of the injector plungers. This could happen on any of the six cylinders. Be certain that the exhaust and intake valves are in a closed position for that cylinder. Stop rotating the engine.

Step 3

Set a dial indicator and pedestal on top of the injector cam roller on the injector rocker arm that first depressed the injector plunger. Make adjustments to the pedestal to ensure that it is at its maximum height.

Step 4

Rotate the engine slowly once again with the 3/4-inch breaker bar. Continue to rotate the engine until the the dial indicator shows no more upward lift. Maximum lift is shown when the needle of the dial indicator stops rotating.

Step 5

Loosen the lock-nut of the injector adjusting screw with a ratchet and socket. Only loosen the nut two full turns. Insert an Allen wrench into the head of the adjusting screw and tighten to 40 inch-pounds.

Step 6

Loosen the same adjusting screw again with the Allen wrench by backing it off 3/4-turn. Use a ratchet and socket to tighten the lock nut to between 30 and 35 foot-pounds. The injector is now set.

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