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Test T - CFI Fuel Control

NOTE: Fuel contaminated engine oil may affect 41, 42, 43, 91, 92 and 93 service codes. If this is suspected, remove PCV from valve cover and repeat QUICK TEST. If problem 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 ). 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 is correct, go to next step.
  2. With pressure gauge installed, cycle key from OFF to ON a few times to pressurize system. Disconnect fuel pump relay. Crank engine for 5 seconds and take pressure reading immediately after finishing cranking. If pressure reading is 10-20 psi (.7-1.4 kg/cm2 ) after 5 seconds of cranking, EEC system is not at fault for no start. If problem is rough running, missing, fuel code, or pressure is incorrect after 5 second crank, 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).
  3. Turn key OFF. Set DVOM to 200 ohm range. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leave ECA disconnected. Measure resistance between test pins 57 and 58 and between tests pins 57 and 59. If resistance is less than 1.5 ohms or greater than 3.5 ohms, service the harness/connectors on the suspect injector for opens or shorts. If okay, replace injector. If resistance is 1.5 to 3.5 ohms, go to next step.
  4. With key OFF, reconnect ECA through breakout box. Reconnect all injectors. Connect non-powered 12 volt test light between test pins 37 and 58. Crank or start engine. Repeat procedure with test light between test pins 37 and 59. If test light does not come on during either or both tests, check for 12 volt battery power at test pins 37 and 57. If test pins 37 and 57 have 12 volt power, replace ECA and repeat QUICK TEST. If test light is very bright on either or both tests, check circuits to banks 1 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.
  5. Connect tachometer and run engine at steady 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. Reset curb idle and verify ISC hookup (using VECI decal) at end of test procedure. 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, running or driving problem is in area common to all cylinders such as a vacuum leak or fuel contamination.
  6. Code 48 Displayed. Turn OFF and wait 10 seconds. Swap injector connections. Perform KEY ON/ENGINE RUNNING SELF-TEST . If code 48 is still present, return injector connections to their original position and to to next step. If not, return to QUICK TEST and address any other code and/or conditions.
  7. Turn key OFF and wait 10 seconds. Disconnect left EGO sensor at sensor. Repeat KEY ON/ENGINE RUNNING SELF-TEST . If code 48, go to next step. If not, go to step 12).
    NOTE: Areas other than EEC may cause service codes 41 and 42 to be displayed. Check for ignition caused misfires, CANP problems, or engine oil that is contaminated by fuel if service code 42 is displayed. If fuel contamination is suspected, repeat QUICK TEST after removing PCV from valve cover. If this resolves problem, replace engine oil and oil filter. Check for leaking vacuum motor, engine sealing problem, faulty EGR or PCV systems, unmetered air leak between air meter and throttle body, or a lead contaminated EGO sensor if service code 41 is displayed.
  8. Always Lean: Left EGO Sensor. Turn key OFF. Set DVOM to 20 volt scale. Disconnect left EGO sensor from vehicle harness. Connect DVOM to EGO sensor and ground. Disconnect ACT sensor. Start engine and run at about 2000 RPM. If DVOM reading is greater than .5 volt within 1 minute, go to next step. If not, replace EGO sensor and repeat QUICK TEST.
  9. Harness Check: Left EGO Sensor. 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 left EGO sensor connector and test pin 29. If both circuits are less than 5 ohms, go to next step. If not, service as necessary and repeat QUICK TEST.
  10. Short to Ground Check: Left EGO Sensor. With key OFF, ECA disconnected and breakout box installed, set DVOM to 200,000 ohm scale. Measure resistance between test pins 29 (left EGO) and 40. If reading is less than 10,000 ohms, correct cause of resistance to ground and repeat QUICK TEST. If resistance is 10,000 ohms or higher, go to next step.
  11. Left EGO Sensor Lean Code Elimination. Turn key OFF. Reconnect EGO sensor. Make certain that the ACT sensor is still disconnected. Start engine and run at about 2000 RPM for 1 minute. Return to idle. Perform KOER Self-Test. If code 41, inspect for corrosion or damaged pins. If okay, replace ECA and repeat QUICK TEST. If code 41 is not present, EGO sensor is okay. Reconnect ATC and go to step 1).
    NOTE: Areas other than EEC may cause service codes 41 and 42 to be displayed. Check for ignition caused misfires, CANP problems, or engine oil that is contaminated by fuel if service code 42 is displayed. If fuel contamination is suspected, repeat QUICK TEST after removing PCV from valve cover. If this resolves problem, replace engine oil and oil filter. Check for leaking vacuum motor, engine sealing problem, faulty EGR or PCV systems, unmetered air leak between air meter and throttle body, or a lead contaminated EGO sensor if service code 41 is displayed.
  12. Always Lean: Right EGO Sensor. Turn key OFF. Set DVOM to 20 volt scale. Disconnect right EGO sensor from vehicle harness. Connect DVOM to EGO sensor. and engine ground. Disconnect ACT sensor. If DVOM reading is greater than .5 volt within 1 minute, go to next step. If not, replace EGO sensor and repeat QUICK TEST.
  13. Harness Check: Right EGO Sensor. 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 44 and engine block and between left EGO sensor connector and test pin 43. If both circuits are less than 5 ohms, go to next step. If not, service as necessary and repeat QUICK TEST.
  14. Short to Ground Check: Right EGO Sensor. Turn key OFF. Breakout box installed and ECA disconnected. Set DVOM to 200,000 ohms range. Measure resistance between test pins 43 and 40. If reading is 10,000 ohms or greater, go to next step. If less than 10,000, correct cause of resistance to ground and repeat QUICK TEST.
  15. Right EGO Sensor Lean Code Elimination. Turn key OFF. Reconnect EGO sensor. Make certain that the ACT sensor is still disconnected. Start engine and run at about 2000 RPM for 1 minute. Return to idle. Perform KOER Self-Test. If code 91, inspect for corrosion or damaged pins. If okay, replace ECA and repeat QUICK TEST. If code 91 is not present, EGO sensor is okay. Reconnect ATC and go to step 1).
  16. Always Rich: Left EGO Sensor. Turn key OFF and wait 10 seconds. Check for fuel contaminated engine oil, ignition caused misfire and CANP problems. Disconnect vehicle harness at the left EGO sensor. Using a jumper wire, ground vehicle harness EGO circuit at the EGO sensor to the engine block. Repeat KEY ON/ENGINE RUNNING SELF-TEST . If codes 41/48, go to step 18). If not, go to step 17).
  17. Harness Check: Left EGO Sensor. Turn key OFF and wait 10 seconds. Disconnect ECA 60-pin connecter. Inspect for and repair any damaged wiring. Install breakout box. Measure resistance between test pin 49 and left EGO ground at engine block and between left EGO harness connector and test pin 29. If both circuits are less than 5 ohms, disconnect ECA and inspect. If okay, replace ECA and repeat QUICK TEST. If both circuit are greater than 5 ohms, correct harness circuit with resistance greater than 5 ohms and repeat QUICK TEST.
  18. EGO Check: Left EGO Sensor. Set DVOM to 20 volt scale. With EGO sensor disconnected from the harness, connect the DVOM from EGO sensor to engine ground. Disconnect PCV hose. Start engine and run at 2000 RPM. If the DVOM reading is less than .4 volt within 1 minute the EGO sensor is okay. Go to next step. If reading is greater, replace EGO sensor and repeat QUICK TEST.
  19. Always Rich: Right EGO Sensor. Turn key OFF and wait 10 seconds. Check for fuel contaminated engine oil, ignition caused misfire and CANP problems. Disconnect vehicle harness at the right EGO sensor. Using a jumper wire, ground vehicle harness EGO circuit at the EGO sensor to the engine block. Repeat Engine Running Self-Test. If code 91, go to step 21). If not, go to step 20).
  20. Harness Check: Right EGO Sensor. Turn key OFF and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box. Measure resistance between test pin 49 and left EGO ground at engine block and between left EGO harness connector and test pin 29. If both circuits are less than 5 ohms, disconnect ECA and inspect. If okay, replace ECA and repeat QUICK TEST. If both circuits are greater than 5 ohms, correct harness circuit with resistance greater than 5 ohms and repeat QUICK TEST.
  21. EGO Check: Right EGO Sensor. Set DVOM to 20 volt scale. With EGO sensor disconnected from the harness, connect the DVOM from EGO sensor to engine ground. Disconnect PCV hose. Start engine and run at 2000 RPM. If the DVOM reading is less than .4 volt within 1 minute the EGO sensor is okay. Go to next step. If reading is higher, replace EGO sensor and repeat QUICK TEST.
  22. Continuous Codes 41 & 42 Displayed. If code 41 appears it indicates that the fuel system was lean for more than 15 seconds, when it should have been under control of EGO sensor. If code 42 appears, it indicates that the fuel system was rich for more than 15 seconds, when it should have been under control of EGO sensor. Before attempting to correct a code 41 or 42, first diagnose all other complaints such as rough idle or missing. 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.
    • 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 1) in this test.
    • Ignition System. If always in default spark (10 degrees), perform Computed Ignition 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 required. If, at this point, drive problem is still present, perform steps 2) through 5) only.
  23. Codes 43 & 93 Displayed. Run engine at 2000 RPM for 2 minutes. Turn key OFF and wait 10 seconds. Perform KEY ON/ENGINE RUNNING SELF-TEST . If code 43, go to next step. If not, service other codes as necessary.
  24. Codes 43 & 93 Displayed. Check exhaust leaks at manifold or inlet pipe. If there are leaks, service and repeat QUICK TEST. If no leaks, go to next step.
  25. Codes 43 & 93 Displayed. Start engine and let idle. If engine idle quality is poor during and after Quick Test, adjust idle speeds. If not, replace EGO sensor and repeat QUICK TEST.
Fig 1: 3.8L CFI Fuel Control Circuits
G2561
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