GM Full-Size Trucks 1980-1987 Repair Guide

Injection Pump Timing

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See Figures 1 and 2

For the diesel engine's fuel injection system to be properly timed, the marks on the top of the engine front cover (8-379) or injection pump adapter (8-350) must be aligned with the marks on the injection pump flange. The engine must be off when the timing is reset.

On 49 state 8-379s, the marks on the top of the engine front cover are scribe lines. On California 8-379s, the marks are half-circles.

  1. Loosen the three pump retaining nuts. If the marks are not aligned, adjustment is necessary.
  2.  
  3. Loosen the three pump retaining nuts. Special Tool #J-26987 is useful here on the 8-350.
  4.  
  5. Align the mark on the injection pump with the mark on the front cover (8-379) or adapter (8-350). Tighten the nuts to 30 ft. lbs. on the 8-379, and 35 ft. lbs. on the 8-350.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: Diesel injection timing marks, 379 shown. Marks shown are in alignment



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Fig. Fig. 2: Injection pump timing marks location and alignment, 350 diesel shown

Use a3/4 inch open-end wrench on the nut at the front of the injection pump to aid in rotating the pump to align the marks.

  1. Adjust the throttle linkage if necessary.
  2.  

 
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