Fuel Injection Pump Timing Adjustment

Adjusts the timing of the fuel injection pump on a 1966 Corvette 327ci V8 equipped with Rochester fuel injection to ensure proper fuel delivery and engine performance.

Warnings

Tools required

Parts

• Fuel injection pump mounting gasket × 1 — Use OEM specification
• Distributor hold-down clamp bolt × 1 — Use OEM specification if damaged

Preparation

1. Verify engine is at normal operating temperature, then shut off and allow to cool completely (minimum 2 hours).
2. Ensure ignition timing is correctly set to factory specification (typically 8° BTDC at idle with vacuum advance disconnected) before attempting fuel injection pump timing.
3. Verify valve lash is correctly adjusted to factory specification (0.030" intake / 0.030" exhaust hot).
4. Disconnect negative battery cable to prevent accidental starter engagement.
5. Relieve fuel system pressure by loosening fuel inlet line at fuel meter slowly while catching fuel in appropriate container.
6. Position vehicle on level surface with adequate ventilation due to fuel vapors.
7. Gather all special tools required, particularly the fuel injection pump timing adapter specific to Rochester systems.
8. Have factory service manual available with timing specifications for your specific engine code.

Procedure

1. 1

   Verify base ignition timing
   Reconnect battery negative cable temporarily. Start engine and allow to reach normal idle. Disconnect and plug vacuum advance line at distributor. Using timing light, verify ignition timing is set to 8° BTDC (or specification on emissions decal). If timing is incorrect, adjust distributor position before proceeding. Once verified, shut off engine and disconnect battery negative cable again.
2. 2

   Access fuel injection pump
   Remove air cleaner assembly and disconnect breather tubes. Remove the fuel meter cover by removing the 4 cover screws. Carefully set cover aside with gasket attached. Identify the fuel injection pump drive assembly located on the driver's side of the engine, driven by the distributor drive gear.
3. 3

   Remove distributor cap and mark rotor position
   Remove distributor cap by releasing the 2 spring clips. Mark the rotor position on the distributor body using a scribe or paint marker. This ensures accurate reassembly position. Remove rotor by pulling straight up.
4. 4

   Install dial indicator on fuel injection pump
   Install the fuel injection pump timing adapter into the pump body where specified in service manual (typically the pump plunger access port). Mount magnetic base dial indicator to engine with extension positioned so indicator tip contacts the timing adapter. Zero the dial indicator with plunger at bottom of stroke. Rotate engine by hand clockwise (viewed from front) and observe total plunger travel. Full stroke should be 0.110 to 0.115 inches.
5. 5

   Rotate engine to TDC compression stroke cylinder 1
   Using socket on harmonic balancer bolt, rotate crankshaft clockwise until timing mark on balancer aligns with 0° (TDC) mark on timing tab. Verify cylinder 1 is on compression stroke by confirming rotor points to cylinder 1 position (marked earlier). If not, rotate engine one complete additional revolution.
6. 6

   Measure fuel injection pump plunger position at TDC
   With engine at TDC compression stroke cylinder 1, read dial indicator. The fuel injection pump plunger should be at 0.035 inches from bottom of stroke (±0.002 inches). This is the critical timing specification. If reading is within specification, proceed to verification steps. If out of specification, pump timing adjustment is required.
7. 7

   Loosen fuel injection pump mounting
   If adjustment is required, remove the 3 bolts securing the fuel injection pump to the engine block. The pump is located on the driver's side of the block, driven by an intermediate shaft from the camshaft. Carefully note the position of any shims or spacers under the pump mounting flange.
8. 8

   Adjust pump timing position
   With mounting bolts loose, the pump body can be rotated slightly on its mounting pad. Rotate pump body counterclockwise (viewed from pump drive end) to advance timing (increase plunger height at TDC). Rotate clockwise to retard timing (decrease plunger height). Make small adjustments of approximately 0.005 inches at a time. Tighten one mounting bolt finger-tight and recheck dial indicator reading at TDC.
9. 9

   Verify and secure pump position
   Once dial indicator reads 0.035 inches (±0.002 inches) at TDC compression stroke cylinder 1, hold pump firmly in position. Install and torque the 3 mounting bolts in a crossing pattern to snug, then final torque. Recheck dial indicator reading after torquing to ensure pump did not shift. If reading changed, loosen bolts and repeat adjustment.
10. 10

    Verify timing through full rotation
    Slowly rotate engine through two complete revolutions clockwise, observing dial indicator. Plunger should reach full stroke height, return to zero, and return to 0.035 inches when timing mark returns to TDC. This confirms pump drive is not binding and timing is consistent.
11. 11

    Remove timing tools and reinstall distributor components
    Remove dial indicator and magnetic base. Remove fuel injection pump timing adapter and install original plug or cover. Reinstall distributor rotor, aligning with the mark made during disassembly. Install distributor cap and secure with spring clips. Verify cap is fully seated.
12. 12

    Reinstall fuel meter cover and air cleaner
    Inspect fuel meter cover gasket for damage and replace if necessary. Position cover on fuel meter body, ensuring gasket is properly seated. Install the 4 cover screws and torque in crossing pattern to snug. Reconnect breather tubes and install air cleaner assembly.
13. 13

    Reconnect fuel system and check for leaks
    Tighten fuel inlet line at fuel meter to secure connection. Reconnect battery negative cable. Before starting engine, turn ignition key to ON position (without cranking) to pressurize fuel system. Inspect all fuel connections for leaks, particularly at fuel meter and injection pump. Wipe away any residual fuel.

Reassembly

1. Ensure all fuel connections are tight and leak-free before starting engine
2. Verify distributor cap is properly seated and rotor is aligned correctly
3. Confirm air cleaner assembly and breather tubes are properly connected
4. Double-check that no tools or rags are left in engine compartment

Verification

• Start engine and allow to warm to normal operating temperature. Listen for smooth idle and consistent running. Rough idle or hesitation may indicate timing is still incorrect.
• Connect fuel pressure gauge to system and verify fuel pressure is 8-12 PSI at idle (typical specification for Rochester system).
• Road test vehicle under light load and moderate acceleration. Engine should respond smoothly without hesitation, backfiring, or excessive fuel odor.
• Recheck for fuel leaks around all connections after test drive, particularly at fuel injection pump and fuel meter.
• If engine performance is not acceptable, recheck fuel injection pump timing with dial indicator to verify specification was maintained after torquing bolts.

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