Code 42 - Fuel Always Rich
Vehicle must be at normal operating temperature. Disconnect jumper wire between ground and Self-Test trigger. Ensure power is present at choke cap, cold enrichment circuit works, and choke is off.
- Disconnect Thermactor air hose at pump, and vehicle harness at oxygen sensor. Connect a voltmeter between oxygen sensor and ground, then disconnect PCV hose from carburetor. Run engine at 1800 RPM for 60 seconds, then observe voltmeter. If voltage is greater than 0.5 volts, replace oxygen sensor. If voltage varies at less than 0.5 volts, reconnect PCV and oxygen sensor. Go to next step.
- Disconnect vehicle harness from feedback motor on carburetor. Connect a known good motor (with shaft fully depressed) to harness, but leave original motor in carburetor. Turn ignition on. If shaft extends, then retracts slightly, go to next step. If motor does not extend, go to step 4).
- Apply 10-12 in. Hg vacuum to vacuum switches. Start engine and place on high step of fast idle cam. Let engine run for 2 minutes, then force system rich by depressing CVR rod on top of carburetor. Observe test feedback motor. If shaft does not retract, disconnect motor and go to next step. If shaft retracts until flush, turn ignition off, reconnect Thermactor hose to pump, and go to step 7).
- Disconnect MCU connector from MCU, and disconnect feedback motor connector. Check continuity of all wires between feedback motor connector and MCU connector. If resistance in any circuit is more than 5 ohms, repair circuit. If all are less than 5 ohms resistance, go to next step.
- Connect 1 ohmmeter lead to FBCA terminal 687 (terminal that connects to Gry/Yel wire of harness) and other ohmmeter lead to each of 4 outside FBCA terminals in turn. Measure resistance of each FBCA winding. If all resistances are 50-175 ohms at room temperature or above, proceed with test. If any winding is more or less than 50 175 ohms, replace FBCA motor.
- Connect one lead of ohmmeter to engine ground, and test pins from feedback motor connector (except Gry/Yel). If resistance of each circuit is more than 1000 ohms, replace MCU. If resistance of any circuit is less than 1000 ohms, repair circuit.
- With ignition off, connect ohmmeter between feedback motor case and terminal 687 of motor. If resistance is less than 190,000 ohms replace motor. If greater than 190,000 ohms (or infinity), go to next step.
- Remove feedback motor from carburetor. Check for sticking shaft or dirt. Connect harness to motor and turn ignition on. Shaft should extend, then retract when ignition is turned off. If motion is uneven, or shaft rotates, replace motor. Reinstall good motor in carburetor and check vacuum lines, evaporative emission system, and crankcase for fuel dilution.