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Test N - Fuel Control

NOTE: Fuel contaminated engine oil may affect 41 and 42 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 ignition off and wait 10 seconds. Install fuel pressure gauge at Schrader valve. Start and run engine. Fuel pressure must be 25-45 psi (1.8-3.2 kg/cm2 ). If within specifications, go to next step. If not within specifications, check fuel pump and fuel pressure regulator. If engine will not run, cycle ignition on and off several times. After final ignition off, fuel pressure should remain at 35-45 psi (2.5-3.2 kg/cm2 ) for 60 seconds.
  2. The following tests check the fuel injection harness resistance. Disconnect 60-pin connector at ECA and inspect. Connect breakout box and leave ECA disconnected. Turn ignition off and place DVOM on 200 ohm scale. Disconnect electrical harness connectors at injectors for cylinders 2, 3 and 4. Measure the resistance of the following circuits and record readings:
    • Injector 1, between box pins 37 and 58.
    • Disconnect injector 1. Reconnect injector 2. Measure between box pins 37 and 58.
    • Disconnect injector 2. Reconnect injector 3. Measure between box pins 37 and 59.
    • Disconnect injector 3. Reconnect injector 4. Measure between box pins 37 and 59.
    All 4 readings should be 2-3.5 ohms. If so, go to next step. If any are not 2-3.5 ohms, service harness/connector on suspect injector for opens or shorts. If okay, replace injector and repeat Quick Test. Reconnect all injectors.
  3. Turn ignition off. With breakout box connected, connect ECA to breakout box. Connect a non-powered 12 volt test lamp between box pins 37 and 58. Crank engine. Repeat test between box pins 37 and 59. If lamp is dim in both tests, go to next step. If lamp does not light on one or both tests, check that battery power exists at pins 37 and 57. If okay, replace ECA and repeat Quick Test. If lamp is bright on one or both tests, check circuits 95 and 96 for shorts to ground. If okay, replace ECA and repeat Quick Test.
  4. Connect tachometer to engine. Run engine at 2000 RPM. It may be necessary to disconnect ISC motor and use throttle body stop screw to set engine RPM. Disconnect and reconnect injectors one at a time. Note RPM drop for each injector. Each should produce at least a 150 RPM drop. If so, fuel delivery system is okay. Problem may be air/vacuum leak, fuel contamination, or EGR system. If speed does not drop 150 RPM, replace faulty injector and repeat Quick Test. Reconnect ISC, and reset curb idle if required.
  5. Code 42. Non-EEC problems can cause a code 42. Check for fuel contaminated engine oil, ignition misfire or canister purge malfunctions. Turn ignition off and wait 10 seconds. Disconnect vehicle harness at oxygen sensor. Using jumper wire, ground oxygen sensor harness oxygen sensor signal circuit to engine block. Repeat Engine Running Self-Test. If code 41 appears, go to step 7). If no code 41, go to next step.
  6. Turn ignition off and wait 10 seconds. Install breakout box. Check continuity of oxygen sensor harness between oxygen sensor ground on engine block and box pin 49. Also check oxygen sensor harness between oxygen sensor signal circuit and box pin 29. If both are less than 5 ohms, disconnect ECA connector and inspect for damage. If okay, replace ECA and repeat Quick Test. If both not less than 5 ohms, correct circuit with improper resistance and repeat Quick Test.
  7. Place DVOM on 20 volt scale. Disconnect harness at oxygen sensor. Connect DVOM from sensor to engine ground. Run engine at 2000 RPM for 2 minutes. While watching DVOM, disconnect manifold vacuum hose to create vacuum leak. If reading is less than .4 volts, sensor is okay, go to step 1). If more than .4 volts, replace oxygen sensor and repeat Quick Test.
  8. Code 41. Vacuum/air leaks in non-EEC areas can cause a code 41. Check for leaks and correct as required. Turn ignition off. Place DVOM on 20 volt scale. Disconnect harness at oxygen sensor. Connect DVOM between sensor and engine ground. Remove air cleaner. Using standard wooden pencil, prop airflow meter inlet door part way open. Start engine and run at 2000 RPM for 2 minutes. If reading is more than .5 volt at end of 2 minutes, go to next step. If less than .5 volt, replace oxygen sensor and repeat Quick Test.
  9. Turn ignition off and wait 10 seconds. Install breakout box and leave ECA disconnected. Repeat procedure in step 6). If both are less than 5 ohms, go to next step. If either is more than 5 ohms, repair circuit and repeat Quick Test.
  10. Turn ignition off. Breakout box installed; ECA disconnected. Place DVOM on 200,000 ohm scale. Disconnect harness at oxygen sensor. Measure resistance between box pins 29 and 40. If less than 10,000 ohms, correct cause of resistance to ground and repeat Quick Test. If 10,000 ohms or more, oxygen sensor input circuit okay. Disconnect ECA 60-pin connector and inspect for damage. If okay, replace ECA and repeat Quick Test.
  11. Continuous Test Codes 41 & 42. 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 oxygen 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 oxygen sensor. Before attempting to correct a code 41 or 42, diagnose all other complaints such as rough idle, missing, etc., first. Areas to check to isolate fuel control problems are as follows:
    • Unmetered Air. Vacuum/air leaks in canister purge system, PCV, engine sealing or air leaks between airflow meter and throttle body.
    • Oxygen Sensor Fuel Fouled. If fuel fouled spark plugs are observed, make thorough check of ignition system. If oxygen sensor is fuel fouled, run vehicle at high sustained speeds. Followed by a few hard accelerations to burn off contamination.
    • Fuel Pressure. Perform Step 1).
    • Ignition System. If always in default spark (10 degrees), perform Timing Check.
    • Improper Fueling. Lead fouled oxygen sensor.
    • Throttle Position Sensor. If not moving, connect DVOM to box pin 47 and to box pin 46. Turn ignition to 'Run'. Observe meter 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 4) only.
    NOTE: The following steps pertain only to 2.3L Turbo Engine.
  12. Turn ignition off and wait 10 seconds. Place DVOM on 200 ohm scale. Measure resistance between 'Run' circuit and ground on heated oxygen sensor at room temperature. If reading is 2.5-5.0 ohms, go to next step. If less than 2.5 ohms or more than 5.0 ohms, replace heated oxygen sensor.
  13. Turn ignition on. With DVOM on 20 volt scale, connect positive lead to 'Run' circuit and negative lead to ground on heated oxygen sensor harness connector. If 10.5 volts or more, heated oxygen sensor system is okay. Perform diagnosis on non-EEC related components. If less than 10.5 volts, go to next step.
  14. Turn ignition off and wait 10 seconds. With DVOM on 200 ohm scale, measure continuity of heated oxygen sensor harness from ground circuit to battery ground. If less than 5 ohms, service open in the "Run" circuit. If 5 ohms or more, service open in ground circuit.
Fig 1: Fuel Injector Circuits
G1295
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