ROUGH IDLE/SMOKE/HARD START DIESEL NOZZLE RETURN HOSE

CONDITIONS MAY ARISE WHERE THE FUEL RETURN HOSE OR NIPPLE IS DISCONNECTED FROM THE FUEL INJECTION NOZZLE. THE PURPOSE OF THE FUEL RETURN HOSE IS TO RETURN THE FUEL WHICH LEAKS PAST THE PINTLE IN THE INJECTOR NOZZLE, BACK TO THE FUEL TANK. THIS IS A RELATIVELY SMALL AMOUNT OF FUEL. STARTING WITH THE END CYLINDERS ON EACH SIDE OF THE ENGINE, THE FUEL PASSES THROUGH EACH SUCCEEDING NOZZLE. IF A BLOCKAGE OCCURS IN THIS FLOW PATH, PRESSURE WILL BUILD UP AND RESULT IN A SMALL FUEL LEAK OR THE CAP OR HOSE BECOMING DISCONNECTED. ONE CAUSE OF BLOCKAGE IS THE LEAK-OFF NIPPLE ON THE NOZZLE BEING PLUGGED ON THE BOTTOM END. DURING ASSEMBLY OF THE NIPPLE INTO THE NOZZLE BODY, THE EPOXY SEALANT MAY HAVE FLOWED OVER THE HOLE IN THE NIPPLE ON THE BOTTOM END. IF THIS HAPPENS, THE RETURN FLOW OF FUEL IS RESTRICTED (FIGURE 1). TO DETERMINE IF THE HOSE OR NIPPLE FALL OFF WAS CAUSED BY A BLOCKED NOZZLE PASSAGE: 1.REMOVE THE HOSES FROM ALL NOZZLE NIPPLES ON THE SIDE OF THE ENGINE INVOLVED. 2.USING A VACUUM SOURCE, ATTACH IT TO ONE (1) NIPPLE ON A NOZZLE. IF THE NOZZLE NIPPLE END IS PLUGGED, A VACUUM READING WILL RESULT. CHECK EACH NOZZLE. 3.THOSE NOZZLES THAT INDICATE A PLUGGED OR PARTIALLY PLUGGED OPENING WILL GENERATE SOME READING ON THE VACUUM SCALE. 4.TO UNPLUG A SUSPECTED PLUGGED NIPPLE INSERT A SMALL DRILL BIT INTO THE NOZZLE NIPPLE AND TURN BY HAND TO BREAK THE EPOXY COVERING. 5.RECHECK WITH VACUUM. IF UNABLE TO BREAK THE EPOXY BARRIER, THE NOZZLE SHOULD BE REPLACED. 6.REPLACE HOSES AND NIPPLE.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.