Chart A-2 Dwell Fixed Over 50 Degrees

Fig. 021 - Wiring Diagram for Chart A-2 Dwell Fixed Over 50 Degrees. VIN C:

CHART A-2, DWELL FIXED OVER 50°

This is a full lean command that may be caused by:
a. Rich engine condition.
b. Leaking bowl vent valve.
c. Excessive fuel in vapor canister or fuel in crankcase
d. Carburetor needs calibration

Fig. 020 - Chart A-2 Dwell Fixed Over 50 Degrees.:

1. Determines whether problem is related to engine or electronics.
a. Normal response - dwell decreases (rich command) - says electronics (O2 sensor, harness and ECM) are OK; problem is a rich engine condition.
b. This may require a large air leak if engine is very rich. When it is lean enough, the engine will start to run rough.
1a. If plugging the PCV or bowl vent vacuum hose causes the dwell to decrease; that hose leads to the source of the problem.
2. Checks ECM response to a "lean" O2 signal.
a. Normal response - low dwell (rich command) - No dwell change says it is bad ECM.
3. Checks for excessive voltage in O2 line.
a. If under .5 volts, wire and ECM are OK; fault is oxygen sensor.
3a. If over .5 volts, wire is shorted to B+ or it's a fault ECM.