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Test S - Fuel Control

NOTE: See HOW TO USE CIRCUIT TESTS  before performing this test. Fuel contaminated engine oil may affect service codes 41 and 42. If this is suspected, remove PCV valve from valve cover and repeat QUICK TEST  . If problem is corrected, change engine oil and filter.
  1. Turn key off and wait 10 seconds. Install fuel pressure gauge. Start and run engine. Fuel pressure must be 35-45 psi (2.5-3.2 kg/cm2 ). If engine will not run, cycle key from off to on several times to build up fuel pressure. If fuel pressure is outside range, check electric fuel pump and fuel pressure regulator. If fuel pressure is correct, go to next step.
  2. Check that fuel pressure remains at 35-45 psi (2.5-3.2 kg/cm2 ) for at least 60 seconds after key is turned off. If pressure is not maintained, go to step 7). If pressure is maintained, go to next step.
  3. With pressure gauge installed, cycle key from off to on several times to pressurize system. Disconnect fuel pump relay. Crank engine for 5 seconds and take pressure reading immediately after cranking. If pressure reading is 10-20 psi (0.7-1.4 kg/cm2 ) after cranking, EEC-IV system is not at fault for no start. If problem is rough running, missing, fuel code, or if pressure is incorrect after cranking, go to next step.
    NOTE: Make sure that fuel is of good quality and not contaminated by air or water, as pressure readings may be incorrect with bad or contaminated fuel. Also, pressure drop will be greater when engine is cold than when engine is warm. If coolant temperature is 200°F (93°C), pressure should drop approximately 10 psi (0.7 kg/cm2 ) in 5 seconds while a pressure drop of 20 psi (1.4 kg/cm2 ) should occur in 5 seconds with engine coolant at 60°F (15.6°C).
  4. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pins No. 37 and 58 for injector bank one. Measure resistance between test pins No. 37 and 59 for injector bank 2. If both readings are between 1.2 and 1.8 ohms, go to step 6). If both readings are not between 1.2 and 1.8 ohms, go to next step.
  5. With key off, breakout box installed and ECA disconnected, set DVOM on 200-ohm scale. Disconnect all injectors on suspect bank. Connect each injector individually and test resistance between test pins No. 37 and 58 for bank one or between test pins No. 37 and 59 for bank 2. If all readings are not between 2.0 and 2.7 ohms, check harness and connectors on injector for shorted or open circuits. If circuits are okay, replace injector(s) and repeat QUICK TEST  . If all readings are between 2.0 and 2.7 ohms, go to next step.
  6. With key off, breakout box installed and ECA connected, connect all injectors. Connect non-powered 12-volt test light between test pins No. 37 and 58. Crank or start engine. Repeat procedure with test light between test pins No. 37 and 59. If test light does not light on one or both tests, check for 12 volts at test pins No. 37 and 57. If test pins No. 37 and 57 have 12 volts, replace ECA and repeat QUICK TEST  . If test light is bright on one or both tests, check circuits to banks one and 2 for short to ground. If no short is found, replace ECA and repeat QUICK TEST  . If test light glows dimly on both tests, go to next step.
    NOTE: After completing step 7), reset curb idle speed and verify ISC hook-up using vehicle emissions label as a guide.
  7. Connect tachometer and run engine at 2000 RPM. Disconnect ISC and use throttle stop screw to set speed if necessary. Disconnect and reconnect one injector at a time and note RPM drop for each injector. If each injector does not produce at least 150 RPM drop when disconnected, replace faulty injector(s) and repeat QUICK TEST  . If RPM drop is correct for all injectors, problem is in an area common to all cylinders such as vacuum leaks, fuel contamination, EGR, etc.
  8. Code 42 Displayed. This code indicates an always rich condition. Turn key off and wait 10 seconds. Disconnect vehicle harness at HEGO sensor. Set DVOM on 20-volt scale. Turn key on. Measure voltage between HEGO signal and ground at HEGO harness connector. If reading is less than 0.5 volts, go to next step. If reading is greater than 0.5 volts, repair short to power in HEGO signal circuit. Repeat QUICK TEST  .
  9. Turn key off. With HEGO disconnected, set DVOM on 200,000 ohm scale. Measure resistance between key power input and HEGO signal at HEGO sensor. If reading is greater than 10,000 ohms, go to next step. If reading is less than 10,000 ohms, replace HEGO sensor and repeat QUICK TEST  .
  10. Turn key off and wait 10 seconds. Disconnect harness at HEGO sensor. Using jumper wire, ground HEGO circuit at HEGO harness connector to engine block. Repeat KEY ON/ENGINE RUNNING (KOER) SELF- TEST. If service code 41 is displayed, go to step 12). If service code 41 is not displayed, go to next step.
  11. Turn key off and wait 10 seconds. Install breakout box. Measure resistance of HEGO sensor ground circuit between test pin No. 49 and HEGO ground at engine block. Measure resistance of HEGO sensor circuit between test pin No. 29 and HEGO sensor harness connector. If both circuits have less than 5 ohms resistance, disconnect ECA connector and inspect for damage or corrosion. If connector is okay, replace ECA and repeat QUICK TEST  . If both circuits have more than 5 ohms resistance, repair circuit having a resistance greater than 5 ohms. Repeat QUICK TEST  .
  12. Set DVOM on 20-volt scale. Disconnect HEGO sensor from harness and connect DVOM between HEGO sensor and engine ground. Start and run engine at 2000 RPM for one minute. Observe DVOM while disconnecting intake manifold vacuum hose. See Fig 1 . If reading is 0.4 volts or higher, replace HEGO sensor and repeat QUICK TEST  . If reading is less than 0.4 volts, HEGO sensor is okay. Repeat QUICK TEST  .
    Fig 1: Intake Manifold Hose Removal
    G4271
  13. Code 41 Displayed. This code indicates an always lean condition. Start and run engine at 2000 RPM for 2 minutes. Turn key off and wait 10 seconds. Perform KOER SELF-TEST. If code 41 is present, go to next step. If code 41 is not present, go to step 19).
  14. With key off and DVOM set on 20-volt scale, disconnect HEGO sensor from harness. Connect DVOM between HEGO sensor and engine ground. Remove air cleaner in order to reach airflow meter inlet. Use a pencil to prop air meter door in partially open position. Start and run engine at 2000 RPM for 2 minutes. If reading is not greater than 0.5 volts after one minute, replace HEGO sensor and repeat QUICK TEST  . If reading is greater than 0.5 volts after one minute, go to next step.
  15. Turn key off. Install breakout box, leaving ECA disconnected. Measure resistance of HEGO circuit between test pin No. 49 and engine block ground. Measure resistance of HEGO circuit between test pin No. 29 and HEGO sensor connector. If both readings are 5 ohms or higher, repair circuit with high resistance and repeat QUICK TEST  . If both readings are less than 5 ohms, go to next step.
  16. With key off, breakout box installed and ECA disconnected, set DVOM on 200,000-ohm scale. Measure resistance between test pins No. 29 and 40. If reading is less than 10,000 ohms, correct resistance to ground and repeat QUICK TEST  . If resistance is greater than 10,000 ohms, go to next step.
  17. Turn key off and disconnect HEGO sensor. Set DVOM to 200,000-ohm scale. Measure resistance between ground and HEGO signal at HEGO sensor. If reading is greater than 10,000 ohms, go to next step. If reading is less than 10,000 ohms, replace HEGO sensor and repeat QUICK TEST  .
  18. Turn key off and reconnect HEGO sensor. Remove air cleaner in order to reach airflow meter inlet. Use a pencil to prop air meter door in partially open position. Start and run engine at 2000 RPM for 2 minutes. Perform KOER SELF-TEST. If code 41 is present, inspect ECA connector for corrosion or damage. If connector is okay, replace ECA and repeat QUICK TEST  . If code 41 is not present, HEGO input circuit is okay. Go back to step 1).
  19. Turn key off. Set DVOM on 200-ohm scale. With HEGO disconnected, measure resistance between ignition run circuit and power ground at HEGO sensor. With HEGO sensor hot or warm, resistance should be 5-20 ohms. If HEGO is at room temperature, resistance should be 2-5 ohms. If readings are within specifications, go to next step. If not, replace HEGO sensor.
  20. Turn key on, leaving engine off. Set DVOM on 20-volt scale. Measure voltage between ignition run power and power ground at HEGO vehicle harness. If reading is greater than 10.5 volts, HEGO sensor system is okay. Connect HEGO sensor and go to step 14). If reading is less than 10.5 volts, go to next step.
  21. Turn key off and wait 10 seconds. Set DVOM on 200-ohm scale. Measure resistance between battery ground and HEGO ground at harness connector. If reading is less than 5 ohms, repair open in ignition run power circuit. If reading is 5 ohms or more, repair open in ground circuit.
  22. Continuous Codes 41, 42 or 43 Displayed. If code 41 appears it indicates that fuel system was lean for more than 15 seconds. If code 42 appears, it indicates that fuel system was rich for more than 15 seconds. If code 43 appears, it indicates that fuel system was lean at wide open throttle for more than 3 seconds. Before attempting to correct a code 41, 42 or 43, first diagnose all other complaints such as rough idle, missing, etc. Areas to check to isolate fuel control problems are as follows:
    • Unmetered Air. Vacuum or intake air leaks in canister purge system, PCV, engine sealing, or air leaks between airflow meter and throttle body.
    • Lack of Fuel. Check for crimped fuel line, plugged fuel filter, or fouled injectors.
    • HEGO Sensor Fuel Fouled. If fuel fouled spark plugs are observed, make complete check of ignition system. If HEGO sensor is fuel fouled (low output and/or slow response), run vehicle at high (but legal) sustained speeds. Follow speed run with a few hard accelerations to burn off contamination and restore HEGO sensor to correct operation.
    • Fuel Pressure. Perform step 1) of this test.
    • Ignition System. If always in default spark (10 degrees), perform TIMING CHECK  .
    • Improper Fueling. Lead fouled HEGO sensor.
    • TPS. If not moving, check for mechanical damage. Connect DVOM on test pins No. 47 and 46. Turn key on, leaving engine off. Observe DVOM while moving throttle. Reading must increase with throttle opening. If not, replace TPS as necessary. If, at this point, drive problem is still present, perform steps 3) through 6) only.
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