Engine: Troubleshoot

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I strongly recommend getting a scanmaster or datalogger, it makes the diagnostic process much easier!

Scanmaster:

Datalogger:

Great information on what datalog data means

Possible causes of poor idle, engine missing or other problems:

Bad ECU

Check by borrowing a good ECU from a friend

Spark Blowout

Reduce plug gap and see if problem gets better

Bad MAF Sensor (Volume Air Flow Sensor)

Troubleshooting Hints

  • Hint 1: If the engine stalls occasionally, crank the engine and shake the volume air flow sensor harness. If the engine stalls, poor contact of the volume air flow sensor connector is suspected.
  • Hint 2: If the volume air flow sensor output frequency is other than 0 when the ignition switch is turned on (but not starting the engine), faulty volume air flow sensor or engine control module is suspected.
  • Hint 3: If the engine can be run idle even though the volume air flow sensor output frequency is out of specification, troubles are often found in other than the volume air flow sensor itself.

Examples:

  1. Disturbed volume air flow in the air flow sensor
    • (Disconnected air duct, clogged air cleaner element)
  2. Poor combustion in the cylinder
    • (Faulty ignition plug, ignition coil, injector, incorrect compression pressure, etc.)
  3. Air leaking into the intake manifold through gap of gasket, etc.
  4. Loose EGR valve seat
  • Hint 4: Check by borrowing a good MAF sensor from a friend. TT & NA sensors are not the same make sure part numbers match

Service Manual diagnostic proceedure:

IAT Sensor, Intake Air Temperature Sensor

Troubleshooting Hints

  • Check Datalog and make sure value is normal, My car's intake tempuratures are usually 30-60 deg hotter that outside tempuratures when idling and only 20-30 deg hotter than outside when cruising (no boost)
  • Service Manual diagnostic proceedure:

O2 Sensors

Troubleshooting Hints

Throttle Position Sensor

Troubleshooting Hints

  • Hint 1: The throttle position sensor signal is more important in the control of automatic transaxle than in the engine control. Shifting shock and other troubles will be caused if this sensor is faulty.
  • Hint 2: If the output voltage of the throttle position sensor is out of specification, adjust the sensor and check the voltage again. If there is an evidence of disturbed fixed SAS setting, adjust the fixed SAS.
  • Hint 3: Datalogger should show between (8 and 14 ???) at idle and it shoudl increase to ??? when gas pedal is fully depressed.
  • Service Manual diagnostic proceedure:

Closed Throttle Position Switch

Troubleshooting Hints

  • Hint 1: Use datalogger to check the TPS switch, it should switch from on to off if you press on the gas pedal at all, and it should switch from off to on when you left off the gas completely.
  • Hint 2: If the closed throttle position switch harness and individual part check results are normal but the closed throttle position switch output is abnormal, the following troubles are suspected.
    1. Poorly adjusted accelerator cable or auto-cruise control cable
    2. Poorly adjusted fixed SAS
  • Service Manual diagnostic proceedure:

Coolant Tempurature Sensor

Troubleshooting Hints

Vacuum/Boost Leaks

Troubleshooting Hints

Camshaft Position Sensor

Troubleshooting Hints

  • Hint 1: If the camshaft position sensor does not function correctly, correct sequential injection is not made so that the engine may stall, run irregularly at idle or fail to accelerate normally.
  • Hint 2: If the sensor outputs a pulse signal when the ignition switch is turned ON (with the engine not running), a faulty camshaft position sensor or engine control module is suspected.
  • Service Manual diagnostic procedure:

Crankshaft Position Sensor

Troubleshooting Hints

  • Hint 1: If unexpected shocks are felt during driving or the engine stalls suddenly during idling, shake the crankshaft position sensor harness. If this causes the engine to stall, poor contact of the sensor connector is suspected.
  • Hint 2: If the crankshaft position sensor outputs a pulse signal when the ignition switch is turned ON (with the engine not running), a faulty crankshaft position sensor or engine control module is suspected.
  • Hint 3: If the tachometer reads 0 rpm when the engine that has failed to start is cranked, faulty crankshaft position sensor or broken timing belt is suspected.
  • Hint 4: If the tachometer reads 0 rpm when the engine that has failed to start is cranked, the primary current of the ignition coil is not turned on and off. Therefore, troubles in the ignition circuit and ignition coil or faulty ignition power transistor is suspected.
  • Hint 5: If the engine can be run at idle even though the crankshaft position sensor reading is out of specification, troubles are often in other than the crankshaft position sensor.

Examples:

  1. Faulty engine coolant temperature sensor
  2. Faulty idle air control motor
  3. Poorly adjusted reference idle speed

Barometric Pressure Sensor

Troubleshooting Hints

  • Hint 1: If the barometric pressure sensor is faulty, poor driveability is caused at high altitude, in particular.
  • Hint 2: If the pressure indication of the barometric pressure sensor drops significantly during high speed driving, check the air cleaner for clogging.
  • Service Manual diagnostic proceedure:

Fast Idle Air Valve (FIAV)

  • Service Manual diagnostic proceedure:

Idle Speed

Idle Air Controller (IAC)

Electronic Suspsension Control ECU (ESC/CAPS)

Troubleshooting Hints

  • Hint 1: The ECS computer can cause hesitation because it shares an input with the TPS on the ECU. A fried ECS computer will cause strange things to happen but it is usually a horrible hesitation that results in the car not being very drivable.
  • Hint 2: Unhook ECS ECU intruck and see if engine problem goes away.
  • 3SX provides instructions on how to disconnect ECS
This article originated from a thread or post on 3000GT/Stealth International. (1853)