System Performance Check
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This test checks carburetor ability to change air/fuel mixture. Disconnecting M/C solenoid makes carburetor run full rich. Reconnecting it with dwell lead grounded makes carburetor run full lean. RPM normally drops 300-1000 RPM as solenoid is reconnected.
- A) If plugging PCV, purge, or bowl vent hose causes RPM to drop more than 300 RPM, plugged hose that caused 300 RPM or more drop leads to source of problem. If RPM increases as M/C solenoid is connected, this indicates system is running extremely rich. If no faults are found during system checks, service carburetor.
- This test checks for proper control of idle circuit.
- A) Indicates "closed loop" operation. Normal dwell reading is 10-50 degrees but varying. Run engine at 2000 RPM for one minute to ensure O2 sensor is warm.
- B) This indicates an "open loop" condition that can be caused by one of the following: Open O2 sensor circuit or bad sensor; Open coolant sensor circuit; Open circuit No. 413, from ECM terminal No. 14 to ground.
- C) This indicates a full rich command to the carburetor, caused by one of the following: Lean engine condition; Grounded O2 sensor circuit No. 412 to ECM terminal No. 9, or bad sensor; Open circuit No. 413, from ECM terminal No. 14 to ground; Open circuit No. 452 to ECM terminal No. 22; Open in coolant sensor circuit No. 410 or No. 452.
- D) This indicates a full lean command which can be caused by one of the following: M/C solenoid wires reversed; Leaking bowl vent valve, excessive fuel in vapor canister, fuel in crankcase, faulty carburetor calibration or carburetor, or silicone contaminated O2 sensor.
- Checks for proper control of main metering system. Engine speed must be at least 3000 RPM to get into the main metering system operation.
- A) A missing "O" ring between the switching valve solenoid and valve, or a defective valve, may cause air to leak into the exhaust ports at higher RPM only.
NOTE:
SYMPTOMS is located in CCC TESTS W/O CODES article in this section.