Testing Information

The following tools will be needed to perform the diagnostic tests: Dwell meter, digital volt-ohmmeter, tachometer, vacuum gauge and jumper wire.

NOTE: Although most dwell meters should be acceptable, if one causes a change in engine operation when connected to the test location, it should not be used.

To determine air/fuel mixture the dwell meter should be set on the 6-cylinder scale and connected to a pigtail wire test connector leading from the mixture control solenoid or diagnostic connector pin 14. When the dwell meter is connected, do not allow the connector terminal to contact any engine component that is connected to engine ground. This includes hoses that may be electrically conductive.

With a normally operating engine, at partial throttle, the dwell will be between 10 and 50 degrees and will be varying. Varying means the pointer continually moves back and forth across the scale. The amount it varies is not important, only the fact that it does vary. This indicates closed loop operation, indicating that the mixture is being varied according to oxygen sensor input to the MCU.

During idle, WOT, and/or cold operation, the mixture is predetermined by the MCU so the meter pointer will vary only slightly. This is open loop operation, indicating that the oxygen sensor output has no effect on air/fuel mixture.

If there is any question as to whether the system is in open or closed loop operation, richening or leaning out the air/fuel mixture will cause the dwell meter reading to vary more during closed loop operation.

NOTE: The "System Operational Test" should be performed after all repairs on the CEC system have been completed.