GM Full-Size Trucks 1970-1979 Repair Guide

Injection Timing



See Figure 1

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Fig. Fig. 1: Diesel timing marks and injection pump lines

For the engine to be properly timed, the marks on the top of the engine front cover and the injection pump flange must be aligned. The engine must be off when the timing is reset. On 49 states models, align the scribe marks. On California models, align the half-circles.


For the engine to be properly timed, the lines on the top of the injection pump adapter and the flange of the injection pump must be aligned.

  1. The engine must be off for resetting the timing.
  3. Loosen the three pump retaining nuts with tool J-26987, an injection pump intake manifold wrench, or its equivalent.
  5. Align the mark on the injection pump with the marks on the adapter and tighten the nuts. Tighten to 35 ft. lbs. (47 Nm). Use a 3 / 4 in. open-end wrench on the boss at the front of the injection pump to aid in rotating the pump to align the marks.
  7. Adjust the throttle rod. See Step 22 under Fuel Injection Pump removal and installation.