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Home >> GMC >> 1984 >> Forward Control 6.2 J, Automatic, 400/M40 >> Repair and Diagnosis >> Engine Performance >> Ignition System >> Ignition System - HEI (Federal) >> Testing - ESC >> Poor Engine Performance
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Poor Engine Performance

  1. Disconnect 4-pin connector at distributor. Install a jumper wire between pins "A" and "C" of distributor connector. If problem remains, check other causes of poor engine performance.
  2. If problem disappeared, remove jumper wire and reconnect 4-pin connector. Without disconnecting 10-pin ESC connector, attach jumper wire from pin "A" to pin "K". If problem remains, proceed to step 5).
  3. If problem disappeared in step 2), remove jumper wire and disconnect sensor wire from sensor. Measure voltage from sensor terminal to ground. Minimum reading is 80 millivolts at 2000 RPM. If okay, check for engine noises other than detonation that might cause input to sensor. Or, substitute with a known good sensor.
  4. If voltage reading was either high or low in the previous step, disconnect wire from sensor. Measure voltage from terminal to ground, checking again. If high or low, replace sensor. If okay, check sensor wire and shield for open circuit. If okay, check sensor wire for an open and repair sensor connector. If not okay, repair harness.
  5. If in step 2), the problem still existed, remove jumper wire from pins "A" and "K". With engine running, connect positive voltmeter lead to pin "F" and negative lead to pin "K" of 10-pin connector. If reading is under 11.6 volts, repair alternator charging circuit.
  6. If over 11.6 volts, check wires in ESC harness from pins "H" and "K" for open circuits or poor connections. If okay, replace ESC controller; if not, replace or repair harness.
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