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Test Q - Fuel Control

NOTE: See HOW TO USE CIRCUIT TEST  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. With pressure gauge installed, cycle key from off to on several times to pressurize system. Pressure must remain at 35-45 psi (2.5-3.2 kg/cm2 ) for 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 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 for and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pins 37 and 58 for injector bank 1. Measure resistance between test pins 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 37 and 58 for bank 1 or between test pins 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 lamp between test pins 37 and 58. Crank or start engine. Repeat procedure with test lamp between test pins 37 and 59. If test lamp does not light on one or both tests, check for 12-volts at 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 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 7), reset curb idle speed and verify ISC hookup 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 EGO sensor. Using a jumper wire, ground EGO circuit at EGO sensor to engine block. Repeat ENGINE RUNNING SELF-TEST. If service code 41 is displayed, go to step 10). If service code 41 is not displayed, go to next step.
  9. Turn key off and wait 10 seconds. Install breakout box. Measure resistance of EGO sensor ground circuit between test pin 49 and EGO ground at engine block. Measure resistance of EGO sensor circuit between test pin 29 and EGO 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 and repeat QUICK TEST .
  10. Set DVOM on 20-volt scale. Disconnect EGO sensor from harness and connect DVOM between EGO sensor and engine ground. Start and run engine at 2000 RPM for 1 minute. Observe DVOM while disconnecting intake manifold vacuum hose. See Figure. If reading is 0.4-volts or higher, replace EGO sensor and repeat QUICK TEST . If reading is less than 0.4-volts, go to step 1).
    Fig 1: Intake Manifold Hose Removal For Test
    G4271
  11. Code 41 Displayed. This code indicates an always lean condition. With key off and DVOM set on 20-volt scale, disconnect EGO sensor from harness. Connect DVOM between EGO sensor and engine ground. Remove air cleaner in order to reach airflow meter inlet. Use wood 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 1 minute, replace EGO sensor and repeat QUICK TEST . If reading is greater than 0.5-volts after 1 minute, go to next step.
  12. Turn key off. Install breakout box, leaving ECA disconnected. Measure resistance of EGO circuit between test pin 49 and engine block ground. Measure resistance of EGO circuit between test pin 29 and EGO 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.
  13. With key off, breakout box installed and ECA disconnected, set DVOM on 200,000-ohm scale. Measure resistance between test pin 29 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.
  14. With key off, connect EGO sensor. Remove air cleaner and prop airflow meter door partially open with wood pencil. Start and run engine at 2000 RPM for 2 minutes. Perform ENGINE RUNNING SELF-TEST. If code 41 is displayed, check for corrosion or damaged pins at ECA connector. If connector is okay, replace ECA and repeat QUICK TEST . If code 41 is not displayed, EGO sensor input circuit is okay, go to step 1).
  15. Continuous Codes 41 & 42 Displayed. If code 41 appears it indicates that the fuel system was lean for more than 15 seconds. If code 42 appears, it indicates that the fuel system was rich for more than 15 seconds. Before attempting to correct a code 41 or 42, 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.
    • 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).
    • 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 on 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 2: 1.9L & 2.3L EFI Fuel Control Circuits
G4272
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