Chart A-1 Dwell Fixed Between 10 and 50 Degrees

Fig. 007 - Wiring Diagram for Chart A-1 Dwell Fixed Between 10 and 50 Degrees. VIN C:

CHART A-1, DWELL FIXED BETWEEN 10° - 50°

This is an OPEN LOOP condition that may be caused by:
a. An open or grounded oxygen sensor circuit or bad sensor
b. An open coolant sensor circuit
c. An open wire from ECM terminal "20" to ground
d. Carburetor needs calibration

Fig. 006 - Chart A-1 Dwell Fixed Between 10 and 50 Degrees.:

1. This check to see if system will go to CLOSED Loop when the "test" terminal is grounded. If the dwell meter now varies, the problem is the coolant sensor circuit.
2. Check to see if the ECM is able to respond to a rich condition caused by choking the engine. If it does, the problem is a lean engine condition, not electrical.
2a. If dwell increases to over 50° with heavy choking, the fault is an air leak since the ECM was able to respond. If air is going to exhaust ports, disconnect the solenoid(s) for the air control valve. If air still goes to the ports, it is a faulty valve.
3. This step puts a rich O2 signal (about 1 volt) into Terminal "3" of the ECM. Dwell should increase (lean command).
4. Checks output of O2 sensor with full rich command from ECM caused by grounded O2 sensor input.
Normal response, voltage at O2 sensor over .8 volt.