Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1983CHEVELLE/MALIBU V8-305 5.0LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTRELAYS AND MODULES - POWERTRAIN MANAGEMENTRELAYS AND MODULES - COMPUTERS AND CONTROL SYSTEMSENGINE CONTROL MODULETECHNICAL SERVICE BULLETINSECM - KNOCK RETARD DATA STREAM CHANGES
1983 Chevrolet Chevelle/Malibu V8-305 5.0L
ECM - Knock Retard Data Stream Changes
1983 Chevrolet Chevelle/Malibu V8-305 5.0LSECTION ECM - Knock Retard Data Stream Changes
83chevy13
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.
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.
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.