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Code 42 - Fuel Always Rich

After starting engine, allow at least 2 minutes at idle before testing. Disconnect "Functional Test" trigger jumper. Do not block throttle open as Idle Tracking Switch will be activated and invalidate test.

  1. Check choke valve for sticking or binding and repair as necessary.
  2. Disconnect MCU connector and connector at Fuel Control Solenoid (FCS). Measure resistance between MCU pin 20 and FCS connector, then between MCU pin 23 and FCS connector. Resistance in both wires should be less than 5 ohms. If so, go to next step. If resistance is higher, repair wiring.
  3. Check resistance of FCS. If within 28-66 ohms, go to next step. If resistance is not within 28-66 ohm range, replace FCS.
  4. Connect a voltmeter to back of FCS harness connector. Start engine and raise engine speed to 2500 RPM. Measure voltage after 55 seconds. If voltage is less than 10 volts, replace MCU. If voltage is more than 10 volts, proceed to next step.
    NOTE: For the following step, a digital VOM must be used which has an input impedance of at least 10 megohms.
  5. 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 greater than 0.4 volts, go to next step. If less than 0.4 volts, check carburetor (too rich).
  6. Purge exhaust system by immediately disconnecting coil "horseshoe" connector and cranking engine for 10 seconds with throttle wide open. Observe DVOM. If greater than 0.4 volts, replace oxygen sensor. If less than 0.4 volts, check carburetor (too rich).
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