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System Performance Test 4 (Dwell Fixed Greater Than 50 Degrees Spectrum)

  1. Run engine at fast idle, then idle. Remove large vacuum hose to cause a vacuum leak (do not stall engine). If dwell does not change, go to step 2). If dwell changes, check evaporative canister and related valves. If okay, repair carburetor.
  2. Disconnect O2 sensor and ground connector terminal to ECM. See Figure . If dwell drops to less than 10 degrees, go to step 3). If dwell does not change, check ECM connection or replace ECM.
  3. Check voltage on O2 sensor wire from O2 sensor at ECM with digital voltmeter with O2 sensor disconnected. If voltage is greater than .5 volt, go to step 4). If voltage is less than .5 volt, replace O2 sensor.
  4. Repeat voltage check with ECM disconnected. If voltage is less than .5 volt, replace ECM. If voltage is greater than .5 volt, check for short in O2 wiring.
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