DIESEL LOW POWER BLACK SMOKE OPERATION OF EPR VALVE

WHEN INVESTIGATING A CONDITION OF BLACK SMOKE AND LOW POWER, CHECK FOR THE PROPER OPERATION OF THE EXHAUST PRESSURE REGULATOR (EPR) VALVE. THE VALVE IS CLOSED AT IDLE TO INCREASE EXHAUST PRESSURE WHICH INCREASES EGR FLOW TO THE ENGINE. THE EPR VALVE OPENS ABOVE IDLE TO ACHIEVE A NORMAL EGR LEVEL FOR TYPICAL DRIVING. DIESEL ENGINE EXCESSIVE SMOKE AND LOW POWER: A MALFUNCTIONING EPR SYSTEM CAN CAUSE BLACK SMOKE AND LOW POWER. CHECK TO SEE IF THE EPR VALVE IS OPERATING PROPERLY BY FLASHING THE THROTTLE AND OBSERVE THE EPR SHAFT TO SEE IF THERE IS MOVEMENT. IF THERE IS NO MOVEMENT, IT INDICATES A SYSTEM MALFUNCTION. REFER TO THE DIAGNOSTIC SECTION OF THE SERVICE MANUAL, SECTION 6A5.

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.