ECM , Canister Purge Circuit Diagnosis - Section 6E1
Number 87-6(Gasoline)-69 Date 9/87Subject: ECM CONTROLLED CANISTER PURGE CIRCUIT DIAGNOSIS - SECTION 6E1
1987 GRAND PRIX AND FIREBIRD MODELS EQUIPPED WITH A 5.0L LG4 (VIN H) CARBURETED ENGINE
The 1987 subject carbureted engine is equipped with an ECM controlled solenoid that allows vacuum to purge the canister when energized.
Use the information provided with this bulletin for any necessary service needed to functionally check the canister purge system.
CHART C-3CANISTER PURGE SOLENOID CHECK 5.0L (CARB):
Circuit Description:
Canister purge is controlled by a solenoid that allows manifold vacuum to purge the canister when energized. The ECM supplies a ground that is pulse width modulated (turned "ON" and "OFF" several times a second). The duty cycle (pulse width) is determined by the map sensor input. (Engine Vacuum) The duty cycle is calculated by the ECM when the following conditions have been met:
^ Engine run time less than specified.
^ Coolant temperature below a given value.
^ Vehicle speed below a given value.
^ TPS below a given value.
CANISTER PURGE VALVE SOLENOID CHECK5.0L (VIN CODE H) GRAND PRIX AND FIREBIRD (CARB):
Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1. The solenoid should be pulsing as grounding the diagnostic terminal turns "ON" the solenoid.
2. Test light should light if CKT 439 is not open as the test light provides a ground for current flow.
3. Test light is being substituted for solenoid to check if ECM and CKT 428 are OK.
4. The solenoid is normally open, so vacuum should not be able to be drawn. (Zero inches [0"].)
5. Applying 12 volts prevents solenoid from pulsing, allowing some vacuum build-up before bleeding "OFF" internally 3" to 5".
6. The ECM is equipped with a fault protected quad-driver for the canister solenoid so if CKT 428 is not open, the quad-driver is faulty within the ECM or the connector terminal is faulty. The solenoid coil must measure more than 20 ohms. Less resistance will cause the CCP driver to open repeatedly.