Component Tests and General Diagnostics

4-151 ENGINE
A dwell meter, digital volt-ohmmeter, tachometer, vacuum guage and jumper wires are required to test this system.

Although most dwell meters should prove suitable, if the one used causes a change in engine operation when connected to the mixture control (MC) solenoid, it should not be used.

When using the dwell meter, set it on the 6 cylinder scale and connect it to the pigtail wire test connector leading to the MC solenoid. When the dwell meter is connected, do not allow the connector terminal to contact any engine component that is grounded. This also includes hoses since they may be electrically conductive. On a normally operating engine, the dwell at both idle speed and partial throttle will be between 10 degrees and 50 degrees and varying. The amount of variation is not important, only the fact that it does vary. This indicates that the system is in the closed loop and the air/fuel mixture is being varied according to input voltage to the MCU from the oxygen sensor. During wide open throttle (WOT) and/or cold engine operation, the air/fuel mixture will be predetermined and the pointer will only vary slightly. This open loop operation indicates the oxygen sensor output has no effect on the air/fuel mixture. Enrichening or leaning the air fuel mixture will cause the dwell meter to vary more if the system is in the closed loop mode of operation. When diagnosing system, always wear eye protection. Also, when engine is running, keep hands and arms clear of fan, drive pulleys and belts. Do not wear loose clothing and do not stand in direct line with fan blades.