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Test T - Fuel Control

NOTE: See HOW TO USE CIRCUIT TESTS  before performing this test. Fuel contaminated engine oil may affect service codes 41, 42, 91 and 92. If this is suspected, remove PCV valve from valve cover and repeat QUICK TEST  . If problem is corrected, change engine oil and filter. Enter CYLINDER BALANCE TEST  as specified in step 1). For additional information see QUICK  TEST DIAGNOSTIC AIDS, CYLINDER BALANCE TEST  in front of this article.
  1. Perform KEY ON/ENGINE RUNNING (KOER) SELF-TEST  . After last code is displayed, wait 5-10 seconds. Enter CYLINDER BALANCE TEST  by briefly opening throttle for one second. If balance test does not display code 90, go to step 6). If balance test displays code 90 (Pass), go to next step.
  2. Turn key off and wait 10 seconds. Install fuel pressure gauge. Start and run engine. Fuel pressure must be 27-37 psi (1.9-2.6 kg/cm2 ). If engine will not run, cycle key from off to on several times to increase fuel pressure. Pressure must be 35-45 psi (2.5-3.2 kg/cm2 ) with engine off. If fuel pressure is incorrect, check electric fuel pump and fuel pressure regulator. If fuel pressure is correct, go to next step.
  3. Turn key on. If fuel pump does not hold pressure for 60 seconds, go to step 5). If fuel pump holds pressure for at least 60 seconds, go to next step.
  4. With key off and pressure gauge installed, cycle key from off to on several times to pressurize system. Locate and disconnect inertia switch. Crank engine for 5 seconds and take pressure reading immediately after cranking engine. If pressure reading drops 5 psi (0.4 kg/cm2 ) or more after cranking, EEC system is NOT at fault for no start. If problem is rough running, missing, or fuel code, go to next step. If pressure did not drop as indicated, go to step 6).
    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).
  5. Turn key off. Perform KOER SELF-TEST and enter CYLINDER BALANCE TEST  by briefly opening throttle for one second immediately after last service code is displayed. If balance test displays code 90 (Pass), go to DIAGNOSIS BY SYMPTOM TEST  . If balance test does not display code 90, go to next step.
    CYLINDER BALANCE TEST SERVICE CODES

    Service Code Cylinder/Injector No. Breakout Box Test Pin No.
    90 Pass Pass
    10 1 58
    20 2 59
    30 3 12
    40 4 13
    50 5 14
    60 6 15
    70 7 42
    80 8 52
    77 Retest Retest
  6. 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 suspect injector circuit test pin and test pins No. 37 and 57. If reading is not between 15-19 ohms, repair open in harness/connectors on suspect injector circuit. If circuit is okay, replace injector and repeat QUICK TEST  . If reading is between 15-19 ohms, go to next step.
  7. With key off, breakout box installed and ECA disconnected, set DVOM on 200,000-ohm scale. Measure resistance between suspect injector circuit test pin and test pins No. 40 and 60. If reading is less than 10,000 ohms, repair short to ground and repeat QUICK TEST  . If resistance is 10,000 ohms or more, go to next step.
  8. With key off and breakout box installed, connect ECA to breakout box. Connect a non-powered 12-volt test light between test pin No. 37 and suspect injector circuit test pin(s). Crank or start engine. If test light glows dimly, replace injector and repeat QUICK TEST  and CYLINDER BALANCE TEST  . If test light is bright or does not light, replace ECA. Repeat QUICK TEST  and CYLINDER BALANCE TEST  .
  9. Run engine at 2000 RPM for 2 minutes. Turn key off. Wait 10 seconds. Perform KOER SELF-TEST. If code 41 or 91 displays, go to next step. If code 41 or 91 is not present, go to step 21).
  10. Code 41 or 91 Displayed. Turn key off and set DVOM on 20 volt scale. Disconnect appropriate HEGO sensor from vehicle harness. Connect DVOM to HEGO sensor and engine ground. Apply 14 in. Hg vacuum to Manifold Absolute Pressure (MAP) sensor and start engine. If reading is less than 0.5 volts, replace HEGO sensor(s) and then repeat QUICK TEST  . If reading is more than 0.5 volts, go to next step.
    NOTE: Vacuum/air leaks in the following non-EEC related areas may cause code 41 or 91 to be displayed. Check for leaking A/C vacuum actuator and engine vacuum leaks. Check EGR and PCV systems. Check for air leak between airflow meter and throttle body. Check for contaminated HEGO sensor(s). Code 41 is for right HEGO sensor. Code 91 is for left HEGO sensor. Both codes indicate an always lean condition.
  11. Turn key off. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale and measure resistance between test pin No. 49 and engine block ground. Measure resistance between test pin No. 29 and HEGO signal at vehicle harness connector and/or measure resistance between test pin No. 43 and HEGO signal at vehicle harness connector. If all readings are higher than 5 ohms, repair open in appropriate circuit and repeat QUICK TEST  . If all readings are less than 5 ohms, go to next step.
  12. Turn key off. Leave breakout box installed and ECA disconnected. Disconnect appropriate HEGO sensor and set DVOM on 200,000-ohm scale. Measure resistance between test pin No. 29 (right HEGO) and test pin No. 40 and/or between test pin No. 43 (left HEGO) and test pin No. 40. If any reading is less than 10,000 ohms, correct cause of resistance to ground. Repeat QUICK TEST  . If reading is 10,000 ohms or higher, go to next step.
  13. Turn key off. Disconnect appropriate HEGO sensor and set DVOM on 200,000-ohm scale. Measure resistance between HEGO signal and HEGO power ground circuit at HEGO sensor. See HEGO Sensor Circuit Checks. If reading is 10,000 ohms or higher, go to next step. If reading is 10,000 ohms or less, replace appropriate HEGO sensor. Connect MAP sensor vacuum hose and repeat QUICK TEST  .
    Fig 1: HEGO Sensor Circuit Checks
    G6039
  14. Turn key off. Connect ECA and HEGO sensor. Ensure MAP sensor vacuum hose is disconnected and plugged. Apply 10 in. Hg to MAP sensor. Start and run engine at 2000 RPM for one minute. Allow engine to idle. Perform KOER SELF-TEST. If code 41 is still present, check ECA connector for corroded or damaged pins. If connector is okay, replace ECA. Connect MAP sensor vacuum hose and repeat QUICK TEST  . If code 41 is not present, connect MAP sensor vacuum hose. HEGO input circuit is okay. Go back to step 2).
  15. Turn key off and wait 10 seconds. Disconnect appropriate HEGO sensor. Code 42 is for right HEGO sensor. Code 92 is for left HEGO sensor. Set DVOM on 20-volt scale. Turn key on. Measure voltage between HEGO signal and HEGO power ground at HEGO harness connector. If reading is more than 0.5 volts, repair short to power in HEGO circuit. Repeat QUICK TEST  . If reading is less than 0.5 volts, go to next step.
  16. Turn key off and leave HEGO disconnected. Set DVOM on 200,000-ohm scale. Measure resistance from key power input to HEGO circuit at HEGO sensor. If reading is 10,000 ohms or less, replace HEGO sensor and repeat QUICK TEST  . If reading is greater than 10,000 ohms, go to next step.
  17. Turn key off and wait 10 seconds. Disconnect appropriate HEGO sensor. Using jumper wire, connect HEGO circuit at HEGO harness connector to engine block. Repeat KOER SELF-TEST. If codes 41 or 91 are present, remove jumper wire and go to next step. If codes 41 or 91 are not present, remove jumper wire. Disconnect ECA connector and inspect for damage. If connector is okay, replace ECA. Repeat QUICK TEST  .
  18. Turn key off and wait 10 seconds. Disconnect vacuum hose from MAP sensor and connect vacuum pump to sensor. Apply 18 in. Hg of vacuum to MAP sensor. If sensor does not hold vacuum, replace MAP sensor. Connect vacuum hose and repeat QUICK TEST  . If MAP holds vacuum, release vacuum and go to next step.
  19. Using vacuum "T", connect vacuum gauge in intake manifold vacuum hose at MAP sensor. Start engine and note vacuum reading. Turn key off and wait 10 seconds. Remove "T" and vacuum gauge. Reconnect hose to MAP sensor. Connect vacuum gauge at a different intake manifold location. Start engine and note vacuum reading. If readings differ by more than 1 in. Hg, inspect vacuum hoses for leaks, kinks, or blockage. Repair as required. If readings are within 1 in. Hg of each other, go to next step.
  20. Set DVOM on 20-volt scale. With HEGO sensor disconnected from harness, connect DVOM between HEGO sensor and engine ground. Disconnect PCV hose. Start and run engine at 2000 RPM. If reading is less than 0.4 volts within 30 seconds, HEGO sensor if okay. Go back to step 2). If reading is more than 0.4 volts within 30 seconds, replace HEGO sensor and repeat QUICK TEST  .
  21. Turn key on, leaving engine off. Set DVOM on 200-ohm scale. With HEGO disconnected, measure resistance between run circuit and ground at HEGO harness connector. 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.
  22. Turn key on, leaving engine off. Set DVOM on 20-volt scale. Connect positive lead to run circuit and negative lead to ground at HEGO harness connector. If reading is 10.5 volts or greater, HEGO sensor system is okay. Connect HEGO sensor and go back to step 2). If reading is less than 10.5 volts, go to next step.
  23. Turn key off and wait 10 seconds. Set DVOM on 200-ohm scale. Measure resistance of ground circuit from HEGO harness connector to battery ground. If reading is less than 5 ohms, repair open in run circuit. If reading is more than 5 ohms, repair open in ground circuit.
Fig 2: 5.0L SEFI Fuel Control Circuits
G6040
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