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Combustion Computer Test

  1. Connect tachometer to engine. Start engine and warm to operating temperature. Disconnect coolant temperature switch and CTS switch (if equipped). DO NOT ground carburetor switch.
  2. Set engine speed at 1200 RPM. Disconnect oxygen sensor connector at sensor and connect jumper wire from connector end to ground.
  3. An increase in engine speed should be observed (minimum of 50 RPM) for 15 seconds, then return to 1200 RPM. If engine speed does not change, disconnect 4-way "T" at temperature sensor on air cleaner, allowing engine to draw in air.
  4. Repeat test again, if engine speed still fails to change, replace computer. Reconnect 4-way "T". Disconnect jumper wire from ground and connect to battery voltage, engine speed should decrease (minimum of 50 RPM).
  5. If computer fails any of these tests, replace computer. Reconnect wires, return engine to curb idle. Stop engine and remove all test equipment.
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