Chart A3 - Dwell Fixed Over 50°
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- This test determines whether problem is related to engine or electronics. Normal response is dwell decrease, this indicates that oxygen sensor, harness and ECM are okay; problem is a rich engine.NOTE: If engine is very rich, a large air leak may be required to lean mixture. When mixture is lean enough, engine will begin to run rough.
- If plugging the PCV or bowl vent vacuum hose causes the dwell to decrease, that hose leads to the source of the problem.
- This test checks ECM response to a "lean" oxygen sensor signal. Normal response to this test is low dwell. No dwell change indicates a defective ECM. This test also eliminates the possibility of an open sensor wire. An open wire would cause open loop operation and may set Code 13.
- This checks for excessive voltage in oxygen sensor line. If under .55 volt, wire and ECM are okay, fault is in oxygen sensor. If over .55 volt, wire is shorted to battery voltage or ECM is faulty.