D.I.S. Ignition System - RPM Reading
Number: 87-06Section: 6D
Date: OCT., 1986
Subject: D.I.S. IGNITION SYSTEM-R.P.M. READING
Model and Year: 1987 CAVALIER, CORSICA, BERETTA WITH L-4 2.0L (VIN CODE 1) 1987 CELEBRITY WITH 2.5L (VIN CODE U, R) 1987 CELEBRITY, CAVALIER, CORSICA, BERETTA WITH V-6 2.8L (VIN CODE W)
TO: ALL CHEVROLET DEALERS
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.