ENGINEMAN 1 & Cand the manufacturer. The following briefdescription of the procedures for equipment madeby two different manufacturers emphasizes someof these similarities, and further emphasizes theneed for following only the procedures indicatedin the appropriate manufacturer’s technicalmanual.A plunger of a Bosch fuel injection pump canbe loosened by cleaning. However, if the plungerdoes not slide freely in the barrel, both the plungerand barrel should be cleaned with an approvedcleaning fluid, rinsed in clean fuel oil, and blowndry with compressed air. A small quantity of mut-ton tallow should then be placed on the plunger.Working the plunger back and forth and rotatingit in the barrel should remove all gummy deposits.Instructions for Bosch fuel injection equipmentstate that such items as hard or sharp tools orabrasives of any kind should never be used incleaning the pumps.Freeing the sticking plunger in a GM unit in-jector may be done in much the same manner asin a Bosch pump.Stains on plungers may be removed by the useof a limited quantity of jewelers’ rouge on a pieceof soft tissue paper. It is important to rememberthat the plunger should not be lapped to thebushing with an abrasive such as jewelers’ rouge.After a plunger has been cleaned with jewelers’rouge, it must be cleaned thoroughly with dieselfuel before being placed in the bushing. If afterrepeated cleanings, the plunger still does not slidefreely, you may assume that either the plunger orthe bushing is distorted.The principal difference in the cleaning pro-cedures for these two units of equipment is in theuse of abrasives. If the recommended cleaningprocedure for these units fails to loosen theplunger so it will slide freely, the plunger and itsmating part will have to be replaced.Broken Plunger SpringA pump of an injector will fail when theplunger spring breaks and fails to return theplunger after injection has occurred.Factors which contribute to broken plungersprings arefailure to inspect the springsthoroughly and careless handling.Broken plunger springs must be replaced. Alsothey should be replaced when there is evidence ofcracking, chipping, nicking, weakening of thespring, excessive wear, or when the condition ofthe spring is doubtful.Jammed Fuel Control RackIf an engine is to operate satisfactorily, the fuelcontrol rack must be completely free to move.Since the rack controls the quantity of fuelinjected per stroke, any resistance to motion willresult in governing difficulties. When this occurs,the engine speed may fluctuate (decreasing as theengine is loaded; racing as the load is removed),or the engine may hunt continuously or only whenthe load is changed. If the fuel control rackbecomes jammed, it may become impossible tocontrol the engine speed with the throttle. Theengine may even resist securing efforts under suchconditions. Since a sticking fuel control rack cancause serious difficulty, especially in an emer-gency, every effort should be made to prevent itsoccurrence. The best way to check for a stickingfuel control rack is to disconnect the linkage tothe governor and attempt to move the rack byhand. There should be no resistance to movementof the rack when all springs and linkages aredisconnected.A fuel control rack may stick or jam as a resultof a stuck plunger, dirt or paint in the rackmechanism, a damaged rack or gear, or improperassembly. When this jamming or sticking occurs,it is necessary to determine the cause of binding.If it is due to damage, the damaged parts mustbe replaced; if the stickiness is due to the presenceof dirt, a thorough cleaning of all parts will prob-ably correct the trouble. Avoid errors inreassembly and adjustment by carefully studyingthe instructions.Backlash in the Control RackBacklash, looseness, or play in the fuel con-trol rack, like sticking or binding of the rack, willinfluence governing of the engine. Propergoverning is based on the theory that for everychange in speed of the engine, there will be a cor-responding change in the quantity of fuel injected.3-20
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