SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSCHEVROLET1985STEP VAN P20, 4.8 T, AUTOMATIC, 475/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMFUEL INJECTION SYSTEM - 6.2L DIESELREMOVAL & INSTALLATIONINJECTION PUMP SEAL REPLACEMENTTHROTTLE SHAFT SEAL
1985 Chevrolet Step Van P20, 4.8 T, Automatic, 475/M40

Throttle Shaft Seal

1985 Chevrolet Step Van P20, 4.8 T, Automatic, 475/M40SECTION Throttle Shaft Seal
  1. Disconnect ground cables from both batteries. Remove air cleaner and air cleaner intake. Install screens in cylinder heads to prevent entrance of dirt. Disconnect fuel return line and wiring from injection pump.
  2. Mark position of throttle position switch (TPS) or vacuum regulator valve for reassembly. Remove throttle rod and return springs. Loosen fast idle solenoid and move aside. Remove throttle cable bracket.
    3. NOTE: Adjuster provides proper alignment of throttle shaft advance cam for reassembly.
  3. Install Advance Cam Adjuster (J-29601) over throttle shaft with slots of adjuster engaging pin. Place spring clip over throttle shaft advance cam and tighten wing nut. Without loosening wing nut, pull adjuster off throttle shaft to provide alignment for reassembly. See Fig 1.
  4. Drive pin from throttle shaft. Remove throttle shaft advance cam and fiber washer. Remove any burrs from throttle shaft after removing cam. Clean injection pump cover, upper portion of pump, throttle shaft and guide stud area. Place rags in engine valley to catch fuel. Remove injection pump cover and remove screws from cover.
    NOTE: DO NOT  allow any dirt or foreign objects to drop into injection pump after cover is removed. Pump damage may result.
  5. Note position of metering valve spring over top of guide stud for reassembly reference. Note position of guide stud and washer. Remove guide stud and washer. See Figure.
  6. Rotate min/max governor assembly up to provide clearance and remove from throttle shaft. If idle governor spring becomes disengaged from throttle block, reinstall with tightly wound coils toward throttle block.
  7. Remove throttle shaft and inspect. If damaged or worn, replace. Inspect throttle shaft bushings for damage, wear or leaks. If bushing replacement is required, pump must be sent to authorized repair station.
  8. Remove throttle shaft seals. DO NOT  cut seals for removal. A nick on shaft will cause leakage. Lightly coat new seals with grease. Install seals on shaft without cutting seals on sharp edges of shaft.
  9. Carefully slide shaft into pump until min/max governor assembly will slip onto throttle shaft. Rotate governor downward and hold in position. Slide shaft and governor into place.
  10. Install new fiber washer, throttle shaft advance cam (DO NOT  tighten cam screw) and throttle shaft drive pin. Align advance cam so advance cam adjuster can be reinstalled over throttle shaft. Install pin in slots and spring clip over advance cam.
  11. Insert .005" (.13 mm) feeler gauge between white washer on throttle shaft and pump housing. Squeeze throttle shaft and tighten cam screw. Remove adjuster.
  12. Install guide stud with new washer. Ensure that upper extension of metering valve spring rides on top of guide stud. Tighten guide stud.
    13. NOTE: Screws must be removed from cover before installing cover to prevent screws from falling into pump.
  13. Hold throttle in idle position. Install new pump cover seal. Make sure cover screws are removed from cover. Position cover about 1/4" forward (toward shaft end) and about 1/8" above pump. See Figure.
  14. Using care not to cut seal, move cover rearward and downward into position. Install cover screws with flat washer against cover. Use care not to drop lock washers or flat washers into pump. Tighten screws. Install vacuum regulator or TPS.
  15. Reconnect negative battery cables to both batteries. Turn ignition switch to "RUN" position. Momentarily touch Pink solenoid wire to solenoid. A clicking noise should be heard as wire is connected and disconnected at solenoid. If clicking noise is heard, go to step 18. If not, go to step 16.
  16. If clicking noise is not heard, linkage may be jammed in wide open throttle position. Engine MUST NOT be started. Remove cover.
  17. Ground solenoid lead (opposite "hot" lead) and connect Pink wire. With ignition switch in "RUN" position, solenoid in cover should move linkage. If not, replace solenoid and repeat step 15. Minimum voltage across solenoid terminals must be 12 volts.
  18. If clicking noise is heard, connect pump solenoid and HPCA wires. Install fuel return line, throttle cable, throttle cable bracket and return springs. Reposition fast idle solenoid.
  19. Start engine and check for leaks. Idle roughness may occur due to air in fuel system. Allow plenty of time for air to be purged from system. Engine may have to be stopped to allow air in injection pump to rise to top of pump for purging.
  20. Remove cylinder head screens. Install air cleaner intake and air cleaner.
NOTE: The following seals must be replaced with the injection pump removed from the engine. For problems not covered in this article, pump must be removed and taken to an authorized repair station.
RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

Shop Manual-Ready ToolsFree Quote CheckQuote Shield Pro

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.