Fuel Always Rich
Components controlled by the MCU system in this test are the oxygen sensor, fuel control solenoid, MCU module, and thermactor air valve. Components which are not controlled by the MCU system, but could cause code fault are: faulty carburetor (high float level or no power to choke plate), misfiring spark plugs (coil or distributor), restricted air cleaner, restricted PVS, faulty air pump (belt or pulley), and/or throttle kicker always on. Anything which adds fuel or restricts air should be investigated as possible cause.
After starting engine, idle engine for at least 2 minutes before testing. Disconnect jumper wire from "trigger socket".
- Check choke valve for sticking or binding. Repair as required and retest.
- Disconnect harness connectors at MCU and FCS. Measure resistance between MCU pin 20 and FCS connector, then between MCU pin 23 and FCS connector. Resistance in both wires should be 5 ohms or less. If so, go to next step. If resistance is higher, repair wiring and retest.
- Disconnect harness at FCS and check resistance at FCS. See View A in .Fig 1 . If within 28-66 ohms, go to next step. If resistance is not within range, replace FCS and retest.
- Reconnect FCS. Turn key on, but do not start engine. Connect positive lead of voltmeter to back of solenoid harness connector (circuit 687) and negative lead to ground. See View B in Fig 2 . Start engine and idle at 2500 RPM. After 55 seconds, observe voltmeter. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, repair open circuit and retest.
- Turn ignition off. Connect negative lead of voltmeter to back of solenoid harness connector (circuit 95) and positive lead to battery positive terminal. See View C in Fig 2 . Start engine and idle at 2500 RPM. Observe voltmeter after 55 seconds. If voltage is 10 volts or less, replace MCU and retest. If voltage is greater than 10 volts, go to next step.
- Disconnect oxygen sensor from harness. Connect DVOM between sensor and ground, with switch in lowest voltage position. Start engine and run at 2000 RPM for 1 minute to warm up sensor. Turn engine off and immediately check DVOM reading. If 0.4 volts or greater, go to next step. If less than 0.4 volts, MCU system is operating properly. Check non-controlled components.
- Purge exhaust system by immediately disconnecting coil "horseshoe" connector and cranking engine for 10 seconds with throttle wide open. Observe DVOM after cranking. If 0.4 volts or greater, replace oxygen sensor and retest. If less than 0.4 volts, check carburetor (too rich).