EL Camino V8-305 5.0L (1984)
![background image](/chevrolet/el_camino/v8-305_5.0l/Page-439001.png)
Engine Control Module: Technical Service Bulletins
ECM - Knock Retard Data Stream Changes
Number:
84-39
Section:
6D (VIy)
Date:
Dec., 1983
Subject:
KNOCK RETARD DATA STREAM CHANGES
Model and Year:
1983-1/2 AND 1984 CAMAROS, CORVETTES, MALIBU, MONTE CARLOS, AND CALIFORNIA LIGHT DUTY TRUCKS
EQUIPPED WITH ELECTRONIC SPARK CONTROL (KNOCK RETARD)
TO:
ALL CHEVROLET DEALERS
Due to assembly line testing procedures, ECM data stream changes were made to measure signals from the knock sensor to the ECM. Prior to this
change data stream provided direct degrees of retard as transmitted from the ECM.
In order that meaningful diagnosis can be made to determine if the engine ESC system is operating properly, the following explanation is being provided.
1981, 1982 and early 1983 with ESC would provide the direct degree of retard taking place when the ALDL scan tool was placed in the knock retard
mode. The reading on the scan tool would be any number from 0 to 19. The number would be the actual degrees of retard command as issued by the
ECM.
1983-1/2 and 1984 models with ESC do not duplicate direct degrees of retard on the scan tool. The numbers seen when the knock retard mode or spark
mode is selected will be any number from 0 and 255. A fixed number indicates no retard is taking place. If retard is taking place, the numbers will
continually increase up to 255 and "roll over" to start again. Small increments of increase indicate small degrees of retard whereas large increments
indicate large degrees of retard (up to 19~).
A properly operating system indicates any reading from 0 to 255 which remains steady at steady throttle opening and if the throttle is snapped to WOT
with any detonation occurring, and incremental 1 or 2 count increase will be displayed indicating that some retard took place.
If an ESC malfunction, disconnect, or electrical interference is being picked up on the sensor, large count increases will be seen even at idle. If engine or
transmission noises are picked up by the sensor, count increases will also be seen indicating that spark is being retarded. EXAMPLES: rocker arm, rods,
bearings, carbon, transmission gear or front pump noises.