Injector Maintenance and Testing

provided. All pump tests should be made with the testing fuel oil temperature between 90°F and 100°F. Now you are ready to conduct the test. Open the fuel shutoff valve and manifold orifice valve. Open the stand throttle, start and run the pump at 500 rpm until the manifold pressure gauge shows the recommended pressure. If the pump does not pickup the specified pressure, check for closed valves in the suction line or an air leak. If the pump is newly re-built, run it at 1500 rpm for 5 minutes to flush the pump and allow the bearings to seat. Continue to run the pump at 1500 rpm and turn the rear throttle stop screw in or out to find the maximum manifold pressure at full throttle. NOTE With a standard governed pump, the throttle screws will be readjusted later. If the pump has a variable speed governor, the throttle shaft is locked in full-throttle position; do not readjust. On a dual or torque converter governor pump, the throttle must be locked in the shutoff position and the converter-driven governor idle-adjusting screw turned in until the spring is compressed. The converter-driven governor must be set on the engine. The pump idle speed is set by closing the bypass and manifold orifice valves and opening the idle orifice valve. Set the pump throttle to idle and run at 500 rpm. To decrease or raise the idle pressure, add or remove shims from under the idle spring. Remember not to set the idle screw until you have adjusted the throttle screws. Once the tests and adjustments have been completed according to the specifications recommended by the manufacturer, remove the pump from the test stand. Make sure the suction fitting is not removed or disturbed. Next, loosen the spring pack cover and drain the pump body. Cover all openings and bind fittings with tape until you are ready to install the pump. Injector Maintenance and Testing In the PT fuel system, fuel is metered by fuel pressure against the metering orifice of the injector. Any change in fuel pressure, metering orifice, or timing will affect the amount of fuel delivered to the combustion chamber. The following two things will interfere with the normal functions of injector orifices: 1. Dirt or carbon in the orifices or in the passages to and from the orifices; and 2. A change in the size or shape of the orifices, particularly caused by improper cleaning of the orifices After soaking dirty injectors in a cleaning solvent to remove the carbon, be sure to dip the injectors in a neutral rinse, such as mineral spirits, and then dry them. NOTE Never use cleaning wires on PT fuel injector orifices. Be sure to use a magnifying glass to inspect the injector orifices for damage. When the injector orifices are damaged, they cannot be made to function properly and must be replaced. Check the injector for a worn plunger or injector body. Worn injectors may cause engine oil dilution from excessive plunger to body clearances. Dilution may also result from a cracked injector body or cup or a damaged O ring. To check the injector for leakage, assemble it. Remember to plug off the injector inlet and drain connection holes; then mount the injector on the injector test stand. Test the injector at a maximum of 1000 psi with the fuel flowing upward through the cup spray holes. If the counterbore at the top of the injector body falls with fuel in less than 15 seconds, the plunger clearance is excessive and may cause engine oil dilution. During this check inspect the injector for leaks around the injector cup, body, and plugs. If the injector does not pass the test and checks, remove the damaged parts and replace them with new parts. Any time you remove an injector plunger, use the lubricant recommended by the manufacturer when you replace the plunger in the injector body. If the injector plunger does not seat in the injector cup, change the cup rather than trying to lap the plunger and cup together. Lapping changes the relationship between the plunger groove and metering orifice and disturbs fuel metering. Always use a new injector cup gasket when you assemble the cup to the injector body to avoid distortion of the cup. When the cup is tightened to the injector body, the gasket compresses everywhere, except under the milled slot on the end of the injector body. Then, if the gasket is reused, the uncompressed areas may cause the injector cup to cock and prevent the injector plunger from seating properly. 5-29