POSSIBLE INCORRECT RPM READING DIRECT IGNITION SYSTEM

VEHICLES AFFECTED: 1987 L-4 2.0L (VIN 1) IN 'J' AND 'L' VEHICLES, L-4 2.5L (VIN U,R) IN N,A AND P VEHICLES; AND V-6 2.8L (VIN W) IN A, J AND L VEHICLES

Direct Ignition Systems (D.I.S.) will deliver two high-voltage pulses per wire during the engine's four stroke operation. This operational characteristic may make reading RPM with an inductive pickup clipped onto a spark plug wire potentially incorrect.

Some inductive pickups when properly used will give an accurate RPM or double reading. Verification of the equipment's accuracy should be made against the ALDL diagnostic connector RPM reading. The diagnostic "scanner" plugged into the ALDL connector running in the "open mode" will give the correct RPM reading along with other useful data.

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.