GM Full-Size Trucks 1988-1998 Repair Information

Fuel Injection Pump

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REMOVAL & INSTALLATION



See Figures 1, 2 and 3



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Fig. Fig. 1: Accelerator cable linkage



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Fig. Fig. 2: Rotate the crankshaft so that the injection pump drive gear bolts become visible through the hole



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Fig. Fig. 3: Injection pump mounting

  1. Disconnect both batteries.
  2.  
  3. If necessary, remove the fan and fan shroud.
  4.  
  5. Remove the intake manifold.
  6.  
  7. Remove the fuel injection lines.
  8.  
  9. If applicable, disconnect the accelerator cable at the injection pump, and the detent cable (see illustration) where applicable.
  10.  
  11. Disconnect the fuel inlet line from the pump.
  12.  
  13. Tag and disconnect the necessary wires and hoses at the injection pump.
  14.  
  15. Disconnect the fuel return line at the top of the injection pump.
  16.  
  17. If necessary for access, remove the air conditioning hose retainer bracket if equipped with A/C.
  18.  
  19. Remove the oil fill tube, including the crankcase depression valve vent hose assembly.
  20.  
  21. Remove the grommet for the oil filler tube.
  22.  
  23. Scribe or paint a matchmark on the front cover and on the injection pump flange.
  24.  
  25. The crankshaft must be rotated in order to gain access to the injection pump drive gear bolts through the oil filler neck hole.
  26.  
  27. Remove the injection pump-to-front cover attaching nuts. Remove the pump and cap all open lines and nozzles.
  28.  

To install:
  1. Replace the gasket.
  2.  

Make sure the locating pin on the pump hub goes into the slotted hole on the driven gear and not the hole in the gear.

  1. Align the locating pin on the pump hub with the slot in the injection pump driven gear. At the same time, align the timing marks.
  2.  
  3. Attach the injection pump to the front cover, aligning the timing marks before tightening the nuts to 30 ft. lbs. (40 Nm).
  4.  
  5. Install the drive gear-to-injection pump bolts. Tighten the bolts to 20 ft. lbs. (25 Nm).
  6.  
  7. Install the grommet for the oil filler tube and the tube.
  8.  
  9. Install and tighten the fuel feed line at the injection pump to 20 ft. lbs. (25 Nm).
  10.  
  11. Attach the fuel return line and all harness connections.
  12.  
  13. Install the injection lines and the intake manifold.
  14.  
  15. Connect the negative battery cables.
  16.  
  17. Check the injection timing.
  18.  
  19. Start the engine and check for leaks.
  20.  

INJECTION TIMING ADJUSTMENT



1988-94 Models

See Figures 4, 5 and 6

Special tool J-26987, or its equivalent, will be necessary for this procedure.

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.
  2.  



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Fig. Fig. 4: Injection pump locating pin-1988-94 models



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Fig. Fig. 5: Injection pump timing alignment marks-1988-94 models



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Fig. Fig. 6: Slot in the injection pump-1988-94 models

  1. Loosen the three pump retaining nuts with tool J-26987, an injection pump intake manifold wrench, or its equivalent.
  2.  
  3. Align the mark on the injection pump with the marks on the adapter and tighten the nuts. Tighten to 30 ft. lbs. (40 Nm). Use a 3 / 4 in. (19.05mm) open-end wrench on the boss at the front of the injection pump to aid in rotating the pump to align the marks.
  4.  
  5. Adjust the throttle rod.
  6.  

1995-98 Models

The use of a suitable scan tool is required to check or adjust the injection timing.

  1. Start the engine and bring it to operating temperature.
  2.  
  3. Attach the scan tool and activate the time set. (If the time set function is activated properly the diesel injection time on the scan tool will read 0.0 degrees.
  4.  

The actual injection time on the scan tool will fluctuate. The average reading should be 3.5 degrees.

  1. Read the actual injection time using the scan tool functions. The reading should be 3.5 degrees.
  2.  

If the engine stalls during time set activation, slightly rotate the injection pump (1mm = 2degrres) towards the drivers side of the vehicle, tighten the flange nuts and repeat time set.

  1. If the injection timing is correct, the adjustment is complete. If the timing is incorrect continue with the procedure.
  2.  
  3. On 1997-98 models, move the A/C compressor to the side to improve access to the injection pump lower mounting bolts.
  4.  
  5. With the engine OFF , loosen the pump flange nuts.
  6.  
  7. Slightly rotate the injection pump in the desired direction (towards the drivers or passenger side of the vehicle) until the set injection time is 3.5 degrees.
  8.  

It is normal for the actual injection time shown on the scan tool screen to fluctuate. Average fluctuation should be 3.5 degrees.

  1. Tighten the pump bolts.
  2.  
  3. If moved, install the A/C compressor and remove the scan tool.
  4.  
  5. Road test the vehicle.
  6.  

 
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