Firebird V8-305 5.0L VIN F FI (1987)
CHART C-5ELECTRONIC SPARK CONTROL (ESC) CHECK5.0L (VIN CODE H) (CARB)
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
1.
This is the ESC functional check. The ECM must be monitoring mph for ESC to function, so check if Code 24 is stored. With engine running
above 850 rpm and drive wheels at least 20 mph, simulate an engine knock by tapping the engine block. This should normally cause an rpm drop
(decrease timing). If it doesn't drop, either the timing is not retarding or is retarded all the time.
2.
This should cause full retard by dropping the voltage at ECM term. "L." Retarded timing should cause an rpm drop.
3.
Normally, voltage should be .08V A/C or higher for a good knock sensor circuit.
4.
"Service Engine Soon" light should be "on" and a Code 43 set because ESC system would be retarded too long. If no light comes on, the ECM is
not retarding the spark because of a voltage on CKT 457 to terminal "L" or the ECM is faulty.
