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Home/Isuzu/Axiom/Isuzu Axiom I (2001-2004)/Repair manual/Testing & Diagnostics/Engine Controls - Basic Diagnostic Procedures: Overview
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Engine Controls - Basic Diagnostic Procedures: Overview Isuzu Axiom I

Testing & Diagnostics ~1200 words

Test Description

Numbers below refer to step numbers in Testing Procedure.

  1. 5 An obvious cause of low fuel pressure would be an empty fuel tank.
  2. 6 The engine will easily start and run if a few injectors are disabled. It is not necessary to test all injectors at this time since this step is only a test to verify that all fuel injectors have not been disabled by fuel contamination.
  3. 7 A blinking test light verifies that PCM is monitoring the 58X crankshaft reference signal, and is capable of activating fuel injectors. If there is an open or shorted driver circuit, DTCs P0201-P0206 and a misfire DTC P0300-P0306 should be set.
  4. 19 By using a spark tester, each ignition coil's ability to produce 25,000 volts is verified.
  5. 25 If there is an open or shorted driver circuit, DTCs P0201-P0206 and a misfire DTC P0301-P0306 should be set. All 6 fuel injector driver circuits can be checked at one time without removing the intake manifold if a Fuel Injector test light (J39021-95) is available. For alternative procedure for checking fuel injector driver circuits perform following: With the ignition off, disconnect fuel injector tester Gray 7-pin in-line harness connector. In-line harness connector is bolted to front of right valve cover, below where air duct attaches to MAF sensor. Connect test light (J39021-95) to fuel injector tester in-line harness connector. If any of the LEDs are illuminate constantly or fail to blink when the engine is cranked, repair short or open circuit, or replace PCM if indicated. This procedure only tests fuel injector driver circuits as far as test connection, see step 31 to test fuel injector circuits all the way to the fuel injector.

Numbers below refer to step numbers in Testing Procedure.

  1. 5 An obvious cause of low fuel pressure would be an empty fuel tank.
  2. 6 The engine will easily start and run if a few injectors are disabled. It is not necessary to test all injectors at this time since this step is only a test to verify that all fuel injectors have not been disabled by fuel contamination.
  3. 7 A blinking test light verifies that PCM is monitoring the 58X crankshaft reference signal, and is capable of activating fuel injectors. If there is an open or shorted driver circuit, DTCs P0201-P0206 and a misfire DTC P0300-P0306 should be set.
  4. 19 By using a spark tester, each ignition coil's ability to produce 25,000 volts is verified.
  5. 25 If there is an open or shorted driver circuit, DTCs P0201-P0206 and a misfire DTC P0301-P0306 should be set. All 6 fuel injector driver circuits can be checked at one time without removing the intake manifold if a Fuel Injector test light (J39021-95) is available. For alternative procedure for checking fuel injector driver circuits perform following: With the ignition off, disconnect fuel injector tester Gray 7-pin in-line harness connector. In-line harness connector is bolted to front of right valve cover, below where air duct attaches to MAF sensor. Connect test light (J39021-95) to fuel injector tester in-line harness connector. If any of the LEDs are illuminate constantly or fail to blink when the engine is cranked, repair short or open circuit, or replace PCM if indicated. This procedure only tests fuel injector driver circuits as far as test connection, see step 31 to test fuel injector circuits all the way to the fuel injector.

Numbers below refer to step numbers in Testing Procedure

  1. 2 Connect fuel pressure gauge to fuel feed line as outlined in «FUEL PUMP PRESSURE TEST»(ref-133136-S39650653832002021300000) . Wrap a shop towel around fuel pressure connection to absorb any fuel leakage that may occur when installing fuel pressure gauge. With ignition switch on and fuel pump running, fuel pressure indicated by fuel pressure gauge should be 48-55 psi (333-376 kPa). This pressure is controlled by amount of pressure spring inside fuel pressure regulator can provide.
  2. 3 Fuel system that cannot maintain a constant fuel pressure has a leak in one or more of following areas: Fuel pump check valve. Fuel pump flex line. Valve or valve seat within fuel pressure regulator. Fuel injector(s).
  3. 4 Fuel pressure that drops off during acceleration, cruise, or hard cornering may case a lean condition. A lean condition can cause a loss of power, surging, or misfire. A lean condition can be diagnosed using a Tech 2 or equivalent scan tool. If an extremely lean condition occurs, the oxygen sensor(s) will stop toggling. Oxygen sensor output voltage(s) will drop below 500 mV. Also, fuel injector pulse width will increase. When engine is at idle, manifold pressure is low (high vacuum). This low pressure (high vacuum) is applied to fuel pressure regulator diaphragm. Low pressure (high vacuum) will offset pressure being applied to fuel pressure regulator diaphragm by spring inside fuel pressure regulator. When this happens, result is lower fuel pressure. Fuel pressure at idle will vary slightly as the barometric pressure changes, but fuel pressure at idle should always be less than fuel pressure noted in step 2 with engine off.
  4. 16 Check spark plug associated with a particular fuel injector for fouling or saturation to determine if that particular fuel injector is leaking. If checking spark plug associated with a particular fuel injector for fouling or saturation does not determine that a particular fuel injector is leaking, use following procedure: Remove fuel rail, but leave fuel lines and injectors connected to fuel rail. CAUTION: Reduce risk of fire and personal injury that may result from fuel spraying on the engine, by verify that fuel rail is positioned over the fuel injector ports and verify that fuel injector retaining clips are intact. Lift fuel rail just enough to leave fuel injector nozzles in fuel injector ports. Pressurize fuel system by connecting a 10 amp fused jumper between battery voltage and fuel pump relay connector. Visually and physically inspect fuel injector nozzles for leaks.
  5. 17 A rich condition may result from fuel pressure being above 55 psi (376 kPa). A rich condition may cause a DTC P0132 or a DTC P0172 to set. Driveability conditions associated with rich conditions can include hard starting (followed by black smoke) and a strong sulfur smell in the exhaust.
  6. 20 This test determines if high fuel pressure is due to a restricted fuel return line or if high fuel pressure is due to a faulty fuel pressure regulator.
  7. 21 A lean condition may result from fuel pressure below 48 psi (333 kPa). A lean condition may cause a DTC P0131 or a DTC P0171 to set. Driveability conditions associated with lean conditions can include hard starting (when engine is cold), hesitation, poor driveability, lack of power, surging, and misfiring.
  8. 22 Restricting fuel return line causes fuel pressure to rise above regulated fuel pressure. Using scan tool command fuel pump On. Fuel pressure should rise above 55 psi (376 kPa) as fuel return line is pinched with pliers.

Numbers below refer to step numbers Test Procedure

  1. 2 If fuel pump is operating but incorrect pressure is noted, fuel pump wiring is okay and Fuel System Pressure Test chart should be used for diagnosis.

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