ECM Controlled Canister Purge - Circuit Diagnosis
87chevy29GMC NUMBER: 87-T-97
GROUP: 6E - Engine Emissions
DATE: November, 1987
CORPORATE
NUMBER: 716513
SUBJECT: ECM CONTROLLED CANISTER PURGE CIRCUIT DIAGNOSIS
MODELS: 1987 CABALLEROS EQUIPPED WITH 5.0L (VIN CODE H) ENGINES
The 1987 subject carbureted engines are equipped with an ECM controlled solenoid that allows vacuum to purge the canister when energized. Use the information provided with this bulletin whenever a functional check to the canister purge system is necessary. The following charts must be substituted for charts in section 6E-Engine Emissions of the 1987 Caballero Microfiche.
COMPONENT LOCATIONS 5.0L (VIN H/G), 5.7L (VIN 6):
Component Locations 5.0L (VIN H/G), 5.7L (VIN 6)
ECM Connector Terminal End View 5.0L (VIN H & G) & 5.7L (VIN 6):
ECM WIRING DIAGRAM 5.0L (VIN H & G) & 5.7L (VIN 6):
ECM TERMINAL VOLTAGE
5.0L AND 5.7L
This ECM voltage chart is for use with a digital voltmeter to further aid in diagnosis. These voltages were derived from a known good car. The voltages you get may vary due to low battery charge or other reasons, but they should be very close.
THE FOLLOWING CONDITIONS MUST BE MET BEFORE TESTING:
^ Engine at operating temperature ^ Closed Loop ^ Engine idling (for "Engine Run" column)
^ Test terminal not grounded ^ "Scan" tool not installed
CHART C-3
CANISTER PURGE SOLENOID CHICK 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 timeless than specified.
^ Coolant temperature below a given value.
^ Vehicle speed below a given value.
^ TPS below a given value.
CHART C-3CANISTER PURGE VALVE SOLENOID CHECK 5.0L (VIN H & 6) "B" SERIES (VIN Y) "G" SERIES. (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.