Code 4-2 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 that choke is off.

1) With ignition off, disconnect thermactor air hose at pump, and vehicle harness at oxygen sensor. Connect a voltmeter between oxygen sensor and ground. Disconnect PCV hose from carburetor. Run engine at 2400 RPM for 60 seconds, and observe voltmeter.

2) If voltage is greater than 0.5 volts, replace oxygen sensor, and re-test. If voltage is less than 0.5 volts, reconnect PCV and oxygen sensor. Go to next step.

3) Stop engine and turn ignition off. Disconnect vehicle harness from feedback motor on carburetor. Connect a known good motor (shaft fully depressed) to harness; leave original motor on carburetor. Turn ignition switch to "RUN" position. If shaft extends, then retracts slightly, go to next step. If motor does not extend, go to step 5).

4) Using a vacuum pump, apply 10-12 in. Hg vacuum to zone vacuum switches. Start engine and place on high step of fast idle cam. Let engine run for 2 minutes, 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 and reconnect thermactor hose. Go to step 7).

5) With ignition off, disconnect harness connector at MCU and feedback motor. Check continuity of all wires between feedback motor connector and MCU connector. If resistance in any circuit is more than 5 ohms, repair circuit, and re-test. If all are less than 5 ohms resistance, go to next step.

6) Connect 1 lead of ohmmeter to engine ground, and test pins from feedback motor connector (except Gry/Yel wire). If resistance of each circuit is more than 1K ohms, go to next step. If resistance of any circuit is less than 1K ohms, repair circuit, and re-test.

7) Connect ohmmeter lead to feedback connector terminal 687 (Gry/Yel wire) and to each of 4 outside terminals in turn. Measure resistance of each FBCA winding. If all resistances are 50-175 ohms at room temperature or above, replace feedback motor and re-test. If any winding is not 50-175 ohms, go to next step.

8) With ignition off, connect ohmmeter between feedback motor case and terminal 687 (Gry/Yel wire) of motor. If resistance is less than 190K ohms, replace motor, and re-test. If greater than 190K ohms, go to next step.

9) Remove feedback motor from carburetor. Check pintle for binding or damage. Connect harness to motor and turn ignition on. Shaft should extend, then retract when ignition is turned off. If pintle binds, replace pintle and re-test. If motor is damaged or pintle does not move, replace motor, and re-test.

10) If motor is okay, check vacuum line routes, evaporative emission system, bowl vent solenoid, and crankcase for fuel contamination. If these items are okay, replace MCU and re-test.