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Test U - CFI 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.
  1. Install breakout box and connect ECA to box. Turn key on. Set DVOM on 20-volt scale and measure resistance between test pin 5 and 60. If reading is less than 10.5-volts, service open in key power circuit. Repeat QUICK TEST. If reading is 10.5 volts or greater, go to next step.
  2. Install fuel pressure gauge. Start and run engine. Fuel pressure must be 35-45 psi (2.5-3.2 kg/cm2 ). Pressure must remain at 35-45 psi (2.5-3.2 kg/cm2 ) for 60 seconds after key is turned off. If engine has a "no start" problem, cycling the key from off to on a few times will build up fuel pressure. If fuel pressure is outside range, check electric fuel pump and fuel pressure regulator. If fuel pressure does not remain at 35-45 psi (2.5-3.2 kg/cm2 ) for 60 seconds, go to step 6). If fuel pressure is correct, go to next step.
  3. With pressure gauge installed, cycle key from off to on a few times to pressurize system. Locate and 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 system is not at fault for no start condition. If problem is rough running, missing, fuel code, or if fuel pressure is incorrect, 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 is 200°F (93°C), pressure should drop approximately 10 psi (.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. Set DVOM on 200-ohm range. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Measure resistance between test pin 57 and 58, and between test pins 57 and 59. If either reading is less than 1.5 ohms, repair harness and/or connectors on suspect injector for shorts. If okay, replace injector. If either reading is greater than 3.5 ohms, repair harness and/or connectors on suspect injector for opens. If okay, replace injector. If both readings are 1.5 to 3.5 ohms, go to next step.
  5. With key off, breakout box installed, and ECA connected, connect a non-powered 12-volt test lamp between test pin 37 and 58. Crank or start engine. Repeat procedure with test lamp between test pin 37 and 59. If test lamp does not light on one or both tests, check for 12-volts test pins 37 and 57. If test pins 37 and 57 have 12-volts, replace ECA and repeat QUICK TEST. If test lamp is bright on one or both tests, check circuits to injector banks 1 and 2 for short to ground. If no short is found, replace ECA and repeat QUICK TEST. If test lamp glows dimly on both tests, go to next step.
    NOTE: After completing step 6), reset curb idle speed and verify ISC hookup using vehicle emissions label as a guide.
  6. Connect tachometer to engine and run engine at idle. Disconnect and connect one injector at a time and note RPM drop for each injector. If each injector does not produce at least 100 RPM drop when disconnected, replace faulty injector(s) and repeat QUICK TEST. If RPM drop is correct for all injectors, fuel delivery is okay, problem is in area common to all cylinders such as a vacuum leak, fuel contamination, EGR, etc.
  7. Code 41 & 91 Displayed. Verify that both codes are displayed during QUICK TEST. If code 41 and 91 are not displayed, go to step 8). If both code 41 and 91 are displayed, go to step 9).
  8. Turn key off. Swap injector connections. Start engine and perform ENGINE RUNNING SELF-TEST. If original code(s) do not repeat, connect harness to original injectors, then go to step 4). If original code(s) repeat, connect harness to original injectors, then go to next step.
  9. Always Lean: Code 41 & 91 Displayed. Code 41 is for right EGO, code 91 is for left EGO. Turn key off. Set DVOM on 20-volt scale. Disconnect appropriate EGO sensor from vehicle harness. Connect DVOM to EGO sensor and engine block ground. Disconnect ACT sensor. Start and run engine at 2000 RPM. If reading is higher than 0.5-volt within one minute, go to next step. If reading is not higher than 0.5-volts within one minute, replace EGO sensor and repeat QUICK TEST.
  10. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Measure resistance between test pin 49 and engine block and between test pin 29 and left EGO sensor connector. Measure resistance between test pin 44 and engine block and between test pin 43 and right EGO sensor connector. If both circuits are less than 5 ohms, go to next step. If both circuits are not less than 5 ohms, repair open circuits as necessary and repeat QUICK TEST.
  11. With key off, breakout box installed, and ECA disconnected, set DVOM on 200,000 ohm scale. Disconnect appropriate EGO sensor at harness. Measure resistance between test pin 29 (left EGO) and 40, and between test pin 43 (right EGO) and 40. If reading is less than 10,000 ohms, correct cause of resistance to ground and repeat QUICK TEST. If reading is 10,000 ohms or higher, go to next step.
  12. Turn key off. Connect EGO sensor. Make certain that ACT sensor is still disconnected. Start and run engine at 2000 RPM for one minute. Allow engine to return to idle. Perform ENGINE RUNNING SELF- TEST. If code 41 or 91 are still displayed, inspect ECA connector for corrosion or damaged pins. If okay, replace ECA and repeat QUICK TEST. If code 41 or 91 are not displayed, EGO sensor input circuit is okay. Go to step 13).
  13. Reconnect ACT sensor. Repeat QUICK TEST. If code 41 or 91 are displayed, replace ECA and repeat QUICK TEST. If code 41 or 91 are not displayed, go to next step.
  14. Always Rich: Code 42 & 92 Displayed. Turn key off and wait 10 seconds. Disconnect appropriate EGO sensor. Using a jumper wire, ground EGO sensor vehicle harness EGO circuit to engine block. Perform ENGINE RUNNING SELF-TEST. If code 41 or 91 are displayed, go to step 16). If code 41 or 91 are not displayed, go to next step.
  15. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box and set DVOM on 200-ohm scale. Measure resistance between test pin 49 and left EGO engine block ground, and between test pin 44 and right EGO engine block ground. Also measure resistance between test pin 29 and left EGO harness connector, and between test pin 43 and right EGO harness connector. If both circuits are less than 5 ohms, disconnect ECA connector and inspect for damage or corrosion. If okay, replace ECA and repeat QUICK TEST. If both circuits are not less than 5 ohms, repair circuit having a resistance greater than 5 ohms. Repeat QUICK TEST.
  16. Turn key off and wait 10 seconds. Disconnect vacuum hose from MAP sensor. Apply 18 in. Hg vacuum to MAP sensor. If MAP sensor holds vacuum, release vacuum and go to next step. If MAP sensor does not hold vacuum, replace MAP sensor. Connect vacuum hose and repeat QUICK TEST.
  17. 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 I 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.
  18. Set DVOM on 20-volt scale. With appropriate EGO sensor disconnected, connect DVOM to EGO sensor and engine ground. Disconnect PCV hose. Start and run engine at 2000 RPM. If reading is less than 0.4-volts within one minute, EGO sensor is okay, go to step 2). If reading is not less than 0.4-volts within one minute, replace EGO sensor. Repeat QUICK TEST.
  19. Continuous Codes 41 & 42 Displayed. If code 41 is displayed, it indicates that system was lean for more than 15 seconds. If code 42 is displayed, it indicates that fuel system was rich for more than 15 seconds. Before attempting to correct a code 41 or 42, diagnose all other complaints such as rough idle, missing, etc. Areas to check to isolate fuel control problems are as follows:
    • Vacuum/Air Leaks. Vacuum or intake air leaks in canister purge system, PVC system, or engine sealing.
    • EGO Sensor Fuel Fouled. If fuel fouled spark plugs are observed, make complete check of ignition system. If EGO 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 EGO sensor to correct operation.
    • Fuel Pressure. Perform step 2).
    • Ignition System. If always in default spark (10 degrees), perform TIMING CHECK.
    • Improper Fueling. Lead fouled EGO sensor.
    • TPS. If not moving, check for mechanical damage. Connect DVOM to test pins 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.
      Fig 1: 3.8L CFI Fuel Control Circuits
      G2561
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