GM Corvette 1963-1982 Repair Guide

Fuel Injection System-1963-65 Models


See Figures 1 and 2

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Fig. Fig. 1: The fuel injection system is composed of three major components

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Fig. Fig. 2: Exploded view of the air meter

The Rochester fuel injection system was a performance option on 1963-65 327 cubic inch engines. It delivers a constantly regulated air/fuel flow regardless of the engine requirements and eliminates carburetion difficulties caused by cornering or braking. While the fuel injection system is more complex than the ordinary carburetor, it is not beyond the repair capabilities of that average owner/mechanic-provided he/she adheres to procedure and specification recommendations.

The first hurdle is understanding the design of the fuel injector and this is best done by thinking of the unit as three separate systems, interlocked to accomplish a common function. The first system is the air meter and this simultaneously furnishes the fuel meter with an assessment of the load demands of the engine and feeds air to the intake manifold. The intake manifold is designed to ram charge the air as it distributes it to the cylinders. The fuel meter evaluates the air meter signal and furnishes the correct amount of fuel to the nozzles where it is injected into the engine.


The 1963-64 air meter consists of three sub-components: the throttle valve, cold enrichment valve and diffuser cone assembly, and the meter housing. The 1965 air meter was modified to the extent that a choke piston was added and the choke valve stop was relocated in the diffuser cone. This allows an initial choke opening of 10° which increases to 30° after an initial cold start. The throttle valve regulates the flow of air into the manifold and is mechanically actuated by the accelerator pedal. The diffuser cone, suspended in the bore of the air meter inlet, functions as an annular venturi and accelerates the air flow between the cone and the meter housing. The air meter houses the previously mentioned components plus the idle and main venturi signal systems.

The main venturi vacuum signals are generated at the venturi as the incoming air rushes over an annular opening formed between the air meter body and piezometer ring. They are then transmitted through a tube to the main control diaphragm in the fuel meter. The venturi vacuum signal measures the flow of air into the engine and automatically controls the air/fuel ratio. The one exception to this is at idle speeds.

Idle air requirements are handled differently by the fuel injection method. Approximately 40;pc of the idle-speed air flow enters the engine through the nozzle block air connections tapped into the air meter body. Part of the remaining 60;pc flows past the throttle valve which is pre-set against a fixed stop. The remainder enters through the idle air by-pass passage that is controlled by the large idle-speed adjusting screw. Idle speed is adjusted by turning this screw in or out.

Fuel Meter

The fuel meter float-controlled fuel reservoir is basically the same as that found in conventional carburetion. The fuel meter receives fuel from the regular engine fuel pump. The incoming fuel is routed through a 10 micron filter before entering the main reservoir of the fuel meter, where the high pressure gear pump picks it up. This high pressure spur-gear type pump is completely submerged in the lower part of the fuel meter main reservoir. A distributor-powered, flexible shaft drives the pump at 1 / 2 engine speed. Fuel pressures span a range of near zero to 200 psi, according to engine speed. Fuel not used by the engine reenters the fuel meter through a fuel control system. The 1965 fuel meter contains a vent screen and baffle which helps to stabilize the air/fuel mixture.

Fuel Control System See Figure 3

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Fig. Fig. 3: Fuel control linkage

A fuel control system regulates fuel pressure (flow) from the fuel pump to the nozzles. This flow is controlled by the amount of fuel that is spilled or recirculated from the high pressure pump, through the nozzle block, back to the fuel meter spill ports. This is accomplished by a three-piece spill plunger or disc that is located between the gear pump and the nozzles.

When high fuel flow is required, it moves downward, closing the spill ports to the fuel meter reservoir and concentrating the flow to the nozzle circuits. Correspondingly, the spill plunger or disc must be raised to allow the spill ports to be exposed when a low fuel flow is required. This causes the main output of the gear pump to by pass the nozzle circuits and reenter the meter reservoir through the now opened spill ports.

The spill plunger is not mechanically controlled by the accelerator pedal. Fuel control is accomplished by a precisely counterbalanced linkage system sensitive to fuel pressure and diaphragm vacuum. Thus the slightest change in venturi vacuum signal on the main control diaphragm will activate the linkage. One end of the fuel control lever rests against the spill plunger head while the other end connects by a link to the main control diaphragm. The control lever pivots on the roller end of an arm called the ratio lever. When the increased vacuum above the diaphragm forces the control lever upward, the lever pivots on the ratio lever roller and pushes the spill plunger or disc downward. This closes the spill ports and steps up fuel flow to the nozzles. When decreased vacuum above the diaphragm reverses the pivot action, fuel pressure forces the spill plunger upward and permits the spill ports to by-pass fuel into the reservoir, thus fuel flow to the nozzles is reduced.

The diaphragm vacuum-to-fuel pressure ratio, and subsequent fuel/air ratio, is regulated by the position of the ratio lever. As the ratio lever changes position, the mechanical advantage of the linkage system also changes, thus providing the correct fuel/air ratio for each driving condition. As long as engine manifold vacuum exceeds 8 in. Hg (mercury), the ratio lever remains at the economy stop and fuel flow follows the dictates of the main control diaphragm vacuum. A sudden decrease in manifold vacuum moves the ratio lever to the power stop. The resulting increase in the mechanical advantage of the linkage system closes the spill ports and increases full flow to the nozzles.

Starting System

Cold engine starting conditions require richer fuel/air mixtures to compensate for poor fuel evaporation. The absence of an accelerator pump prevents the driver from providing extra fuel by pumping the accelerator pedal. The correct method is to depress the pedal once and then release. This pre-sets the throttle for starting by the fast-idle cam. The vacuum signal generated at cranking rpm is very low and must be boosted. This boost is provided by a spring-loaded, open-cranking signal valve located at the enrichment diaphragm housing. This open valve allows the manifold cranking vacuum to react directly on and lift the main control diaphragm. This closes the spill valve. In addition, the spring-loaded enrichment diaphragm holds the ratio lever at the rich or power stop, thus providing maximum fuel flow to the nozzles. As soon as the engine starts, manifold vacuum overcomes the springs in the cranking signal valve and enrichment diaphragm, and the regular idle system is brought into operation.

The vacuum-controlled, cranking-signal valve circuit was eliminated on 1965 model injectors and replaced by a solenoid-controlled, by-pass fuel circuit. This system delivers the entire output engine fuel pump to the fuel distributor via a by pass line. The fuel is then routed through a check valve and finally arrives at the individual nozzles. The control solenoid is energized when the ignition switch is held in the start position and the accelerator pedal is depressed less than 1 / 3 of its travel. Depressing the accelerator pedal further trips a micro-switch on the throttle linkage and stops fuel delivery to the by-pass circuit.

Idle System

Correct injector operation at idle speed is highly dependent upon the generation of a strong venturi signal and its subsequent transmittal to the control diaphragm. To ensure this signal during cold engine idle, the fast-idle cam holds the throttle valve cracked open. This increases the velocity of air flowing through the venturi, which in turn strengthens the venturi vacuum signal being transported to the main control diaphragm. The electrically heated choke valve remains closed during initial cold engine operation, and this requires the entire air flow to pass through the venturi. This rerouting of the air flow generates a usable venturi signal even at relatively low engine speeds. Intake manifold vacuum acts directly on the enrichment diaphragm. The diaphragm response movement adjusts the ratio lever to the economy stop as soon as manifold vacuum is sufficient to overcome the diaphragm spring. As the electric heating element senses a rise in engine temperature, it relaxes the thermostat and permits the choke valve to open. Air flow through the venturi decreases and the signal generated here drops. The idle signal system now becomes the more dominant signal.

Fuel control during warm engine idle is a result of main control diaphragm response to the idle circuit signal. With the ratio lever already positioned at the economy stop, air now enters through the idle air circuit and the nozzle blocks.


Acceleration is instantaneous at normal driving speeds. Opening the throttle valve increases both air flow and the venturi signal at the main diaphragm. The momentary drop in manifold vacuum causes the ratio lever to move to the power stop position. A calibrated restriction in the main control signal circuit stabilizes the idle signal and adds this to the total signal as long as it is present.

Ratio Lever-Power Stop

The air/fuel ratio requirements for power are basically the same as those necessary for acceleration. The drop in manifold vacuum, caused by a wide-open throttle condition, moves the ratio lever to the power stop. The open throttle also provides a stronger venturi signal through the increased air flow.

Hot Starting/Unloading

Rich mixtures must be prevented during hot starting/unloading situations. Depressing the accelerator pedal to fully open the throttle valve during starting will prevent high vacuum from reaching the cranking signal valve and will facilitate starting.

Hot Idle Compensator

Extremely hot operation conditions can cause rich mixture conditions that detrimentally affect engine smoothness and idling. To remedy this, a thermostatically controlled valve on the top side of the air meter throttle valve allows additional air to bleed into the manifold and restore the idle mixture to a correct ratio.

Idle Speed and Fuel Adjustments See Figures 4 and 5

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Fig. Fig. 4: Idle speed adjustment screw location

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Fig. Fig. 5: Location of the idle mixture adjustment screw

Idle speed and fuel adjustments require pre-setting of the idle-speed and idle-fuel adjusting screws 1 1 / 2 turns out from their fully closed position. Start the engine and adjust the idle-speed screw until 800-850 rpm is obtained. Adjust the idle-fuel screw until the smoothest engine idle is attained. Should the two idle-adjusting screws become completely out of phase, purge the system or stop the engine and repeat the entire preceding procedure.

Fast Idle-Speed and Cold Enrichment Adjustments

Adjust the fast idle-speed by bending the enrichment linkage until clearance between the fast-idle cam and the adjusting screw resembles the illustration. With the engine stopped, crack the throttle valve and manually close the cold enrichment valve. Release the throttle linkage and check to see that the fast-idle is now positioned for cold engine operation. Release the cold enrichment valve, warm the engine, and adjust the fast-idle screw to obtain 2,200 rpm. Make the cold enrichment adjustment by setting the cold enrichment cover to 3 notches lean. Be sure that the valve linkage operates freely.

Ratio Lever Stop Settings See Figure 6

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Fig. Fig. 6: Economy and power stop adjusting screws

This series of adjustments requires the use of a manometer. Attach the manometer in a convenient place on the vehicle and use the two-position bracket so that the most vertical position may be obtained. After the unit has been leveled by means of the leveling vial, open both water manometer valves and see if a zero reading exists. If not, adjust the oil leveling screw. If this fails to zero the indicator, add red oil (specific gravity 0.826). Back off the leveling screw for this procedure.

Remove both hose adapters on the mercury (Hg) manometer and plugs located in the adapters. Install the tee fitting in the most easily accessible fuel nozzle circuit. Attach the fuel pressure line to the tee fitting and the mercury manometer. Check the fuel trap inlet to see that it is properly positioned in the line. Clamp the venturi signal line to the cranking signal valve line and the water manometer. Check the clamp to be sure it is tightly closed on the line. If it isnt, high vacuum during engine cranking will cause the red oil to be lost. Replace the main diaphragm vent tube with the large rubber tube. Adjust the scale of the mercury manometer to read zero inches. Recheck the manometer leveling vial and make any necessary adjustments. This completes the installation.

The economy stop adjustment procedure begins with a visual check of the unit for physical defects. With the engine warmed up, check to see that the unit is operating on the economy stop. Some injectors may be difficult to start with the cranking-signal valve line disconnected. The line may be reconnected during the initial starting procedure.

Increase engine rpm until a 0.5 in. signal is registered on the water manometer. Check the mercury manometer and record its reading. Decrease the engine rpm and repeat the above procedure. Average three readings for best accuracy. To adjust, loosen the locknut and turn the economy stop screw in or out until the mercury manometer reads 0.8 in. ( 0.1 in.) when the water manometer reads 0.5 in.

The power stop readings are obtained with the manometer hooked up as in the previous procedure. Disconnect and plug the vacuum line going to the enrichment diaphragm and the injection unit will operate only on the power stop. Do not prolong this operation or spark plug fouling will result.

Increase the engine rpm until a 0.5 in. signal is reached on the water manometer and check and record the mercury manometer reading. Reduce engine speed and repeat the above operation. Average three readings for the best results. Check the enrichment diaphragm to see that it is not bottoming in the housing. To adjust the power stop, loosen the locknut and turn the adjusting screw until a reading of 1.2 in. ( 0.1 in.) is reached on the mercury manometer when the water manometer reads 0.5 in.


See Figure 7

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Fig. Fig. 7: Removing the fuel pressure lines

  1. Disconnect the washer vacuum line, accelerator linkage, electric choke lead wire, and the bellcrank return spring.
  3. Loosen the flexible hose clamp and slide the hose from the air meter adapter.
  5. Disconnect the fuel line at the filter and the drive cable coupling at the distributor by sliding the cable into the pump housing to disengage it from the distributor, and then pulling it clear. Dont lose the fiber washer on the end of the cable.
  7. Remove the engine/manifold adapter-plate retaining nuts and lift the assembly from the engine.
  9. Install a 3 / 8 in. X 2 in. bolt and nut in each manifold outer mounting-hole to allow the unit to be placed upright on a workbench without damaging the nozzles.
  11. Reverse the above procedure to install.


See Figures 8 through 15

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Fig. Fig. 8: Ratio lever control linkage

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Fig. Fig. 9: Exploded view of the fuel pump piston and valve assembly

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Fig. Fig. 10: Make sure to get the correct nozzle part during assembly

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Fig. Fig. 11: Exploded view of the nozzle assembly

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Fig. Fig. 12: Nozzle block assembly

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Fig. Fig. 13: Whenever a complete nozzle cleaning is made, a fuel nozzle spray pattern check should be performed

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Fig. Fig. 14: Exploded view of the fuel injection pump

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Fig. Fig. 15: View of the spill plunger assembly

  1. The first step in disassembly is to separate the fuel injection unit into its three main components: fuel meter, air meter, and manifold.
  3. Separate the air meter from the injector unit by disconnecting the bellcrank from the pivot shaft and leaving it attached to the air meter. Disconnect the main control signal tube at both ends and remove. Remove the retaining nuts and washers and carefully lift the air meter while simultaneously disconnecting the rubber, nozzle balance tube elbow at the air meter.
  5. Disconnect the enrichment diaphragm tube at both ends, disengaging the tube at the manifold end first. Disconnect the main control diaphragm vent tube at both ends. Invert the injector and drain the fuel reservoir through the cover vent, then disconnect the fuel pressure lines. Remove the lower retaining screws, the single upper bolt, and the short vent tube. Discard the rubber O-ring at the fuel meter end of the fuel line. Remove the fuel meter from the injector unit.
  7. Disassemble the air meter by removing the air cleaner adapter, fast-idle cam pivot screw, diffuser cone assembly, and piezometer ring from the air meter.
  9. Remove the idle-speed and idle-fuel adjusting screws. The throttle valve need not be removed unless shaft binding exists.
  11. Disassemble the fuel meter by removing the diaphragm cover and shield. Carefully remove the diaphragm retaining nut and diaphragm from the control link. The control link must be kept from rotating to prevent damaging the control link.
  13. Remove the nylon splash shield, the fuel bowl cover attaching screws and carefully lift the cover, upper support bracket, and gasket from the meter body. Do not bend the control link. Start the link into the slot, then pry the opposite side upward and turn the shield over the link.
  15. Remove the fuel pump, enrichment housing, and cranking signal valve. Remove the spill plunger cover and filter, spill plunger and sleeve assembly from the fuel meter bore. If the spill plunger separates from the sleeve, use a hooked wire to pull the sleeve out.
  17. Remove the ratio lever and shaft. Rotate the control arm and counterweights on the axle and remove the axle. Remove the control arm and counterweight assembly from the meter body. This will also remove the lead sealing ball on the outer end of the axle shaft.
  19. The fuel pump is secured to the fuel meter by 5 screws. Remove these, noting that the shortest screw is positioned in the 9 oclock position. With pump separated from the fuel meter, scribe reassembly marks on the pump housing.
  21. Remove the cover attaching screws and the cover. Hand pressure is sufficient to pull the drive shaft from the pump drive gear and housing. Use a suitable driver to remove the drive shaft seal from the pump housing. Bear in mind, the fuel meter contains 48 parts in addition to screws. Be careful. Reassembly is the reverse of this procedure.
  23. Nozzles may be disassembled for cleaning but care should be taken to ensure correct reassembly. Never clean nozzle orifices with wire. If a nozzle is dirty, replace it. Should more than one nozzle be found exceptionally dirty, replace the fuel meter filter. Replace nozzles only as complete assemblies and according to the following chart:
  25. Begin disassembly by carefully disconnecting and lifting the fuel lines out of the way. Disconnect either the throttle bell crank or fuel pump drive cable when removing nozzles in their vicinity. Remove the nozzles and nozzle blocks as complete assemblies. Invert the blocks and remove the individual nozzles. Carefully remove the old nozzle gaskets. Disassemble the unit by securing the nozzle body and inserting a drift punch in the head to turn it. Avoid damaging, losing, or mixing parts. Remember: the nozzle orifice discs are assembled with the bright side toward the engine. After cleaning or replacing nozzle assemblies, reinstall them in the nozzle block, using new gaskets. Check to see that the nozzle gaskets remain in position during reinstallation and that the nozzles are properly placed in the nozzle shields. Reassembly is the reversal of this procedure.
  27. A fuel nozzle spray-pattern check should be made whenever a complete nozzle cleaning is made. Drive the gear pump with an electric drill while applying oral vacuum at the main control diaphragm. The latter ensures that all fuel is routed through the nozzle circuit. The spray pattern is correct when each bank of nozzles appears as a single spray when viewed from the end of the assembly.
  29. Spill plunger assemblies are basically the same for all fuel injection units. After removing the assembly from the fuel meter, lubricate with fuel, and check the valve action. Clean or replace the assembly as required.
  31. Reassembly of the air meter is the reversal of the disassembly procedure. At this time, check for throttle shaft binding. If such a condition exists, attempt to remedy by soaking in solvent. If the throttle shaft still binds, disconnect the throttle shaft from the linkage, remove the throttle plate screws, and file the burrs on the shaft. Remove the shaft, clean, rebush and then reassemble. During reassembly, preset the idle-speed and idle-fuel adjusting screws 1 1 / 2 turns out from the bottom.
  33. Fuel meter reassembly is the reversal of the disassembly procedure. When installing the main control diaphragm, keep in mind that the slots in the diaphragm should readily align with the cover attaching screw holes located in the bowl cover. Repeat the reassembly steps until the diaphragm holes line up naturally. Do not force this alignment. If the diaphragm seemed tight when removed, it is defective. The replacement diaphragm should not be installed in the same condition. At this time check the clearance between the housing and the enrichment diaphragm. A minimum of 0.040 in. is required to prevent interference during power stop operation. Adjust the diaphragm shaft length to gain proper clearance.

Check the fuel reservoir float settings before replacing the top cover. Float level should be 2 9 / 32 in. while float drop should be 2 27 / 32 in. Bend to adjust.