System Performance Check
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- 1) This test checks the ability of carburetor main metering system to change the a/f mixture. Disconnecting M/C solenoid makes carburetor operate fully rich and reconnecting it with the dwell lead grounded makes it operate fully lean. Normal response is for RPM to drop (400-1000 RPM, 100 RPM minimum) as solenoid is reconnected.
- 1A) If plugging purge, PCV, or bowl vent vacuum hose causes RPM to drop, that hose leads to source of problem. If RPM increases as M/C solenoid is connected, it indicates the system is running extremely rich. This can be caused by incorrect valve timing.
- 2) Checks for proper control of idle circuit.
- 2A) This is a full rich command to the carburetor. This may be caused by lean engine condition, grounded O2 sensor wire or bad sensor, open wire in ECM terminal No. 20 to ground, or open coolant sensor circuit.
- 2B) This indicates an open loop condition. This can be caused by an open or grounded O2 sensor circuit or sensor, an open coolant sensor circuit, or an open in the wire from ECM terminal No. 20 to ground.
- 2C) This is a full lean command and can be caused by a rich engine condition, leaking bowl vent valve, excessive fuel in vapor canister, fuel in crankcase, or faulty carburetor calibration or carburetor.
- 2D) This is a normal response indicating closed loop condition.
- 3) This test checks for proper control of main metering system. Engine must be running at 3000 RPM or more to activate main metering system.
- 3A) A missing "O" ring between switching valve solenoid and the valve or a faulty valve may cause air to leak to the exhaust at higher RPM only.