Chart A-3 Dwell Fixed Over 50 Degrees

Chart A-3 - Dwell Fixed Over 50~:

Wiring Diagram for Chart A-3 - Dwell Fixed Over 50 Degrees:

CHART A-3 - DWELL FIXED OVER 50°

Test Description:

1. Determines whether problem is related to engine or electronics.

Normal response - dwell decreases (rich command) - says electronics (O2 sensor, harness and ECM) are OK; problem is a rich engine condition.

This may require a large air leak if engine is very rich. When it is lean enough, the engine will start to run rough.

2. If plugging the PCV or bowl vent vacuum hose causes the dwell to decrease, that hose leads to the source of the problem.

3. Checks ECM response to a "lean" O2 signal. Normal response - low dwell (rich command). No dwell change says it is bad ECM. It couldn't be an open wire because that would cause open loop operation and may set Code 13.

4. Checks for excessive voltage in O2 line.

If under .55V, wire and ECM are OK; fault is in O2 sensor which could be the result of silicone contamination. If over .55V, wire is shorted to B+ or a faulty ECM.