Chart A-1 Dwell Fixed Under 10 Degrees

Chart A-1:

Wiring Diagram - Mixture Control Solenoid Dwell:

CHART A-1

DWELL FIXED UNDER 10 DEGREES (LEAN EXHAUST INDICATED)


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. Determines if the problem is CCC related or engine related. Dwell should start increasing as soon as engine is choked and go higher as it is choked more until it goes over 50 degrees. With severe choking, the dwell could move up the scale momentarily even if it is not engine related, but it will move right back to a low dwell. If dwell responds, the problem is a lean engine.

2. Checks for ECM response to input of 02 sensor circuit. The voltmeter is used to put a voltage on the oxygen sensor circuit to simulate a rich condition. Dwell should increase (a lean command) if ECM and harness are good.


3. Checks for normal coolant sensor input. The coolant temperature required to enable "Closed Loop" operation varies with start-up coolant temperature, but maximum is 75 degrees C. The engine should be above 75 degrees C if the thermostat is open, allowing the upper radiator hose to get hot.

4. Check for 02 sensor circuit problem or high TPS input signal which could cause a full rich command.

5. Lists causes of a lean condition which could result in a full rich command.

Diagnostic Aids:

Dwell fixed under 10 degrees indicates a full rich command to the carburetor. This could result from:

Severe engine misfire; refer to DIAGNOSIS BY SYMPTOM - NO TROUBLE CODE STORED.

False lean 02 sensor signal voltage (low voltage).

Very cold coolant temperature indication.

High TPS voltage signal.