Test C1 - Fuel Control

To prevent replacement of good components, be aware of the following non-EEC areas which may be cause of driveability concerns:

• Ignition coil, distributor cap or rotor
• Faulty spark plugs or wires
• Faulty CANP system
• DIS ignition system
• EGR valve and gasket
• Air filter
• Fuel or engine oil contamination
• Poor electrical ground
• Faulty fuel pressure
• Intake or exhaust manifold leaks
• Engine below normal operating temperature

This test is intended to diagnose only the following components:

• HEGO sensor
• HEGO signal and ground circuit
• HEGO sensor connection
• Vacuum systems
• Fuel injector
• ECA
• Electrical circuits HEGO GRD, HEGO, INJ 1-8, and VPWR

Fig 1: MPFI Test Schematic

1. Checking Fuel Pressure. Turn ignition key off, wait 10 seconds. Install fuel pressure gauge. Verify that manifold vacuum supply is connected to fuel pressure regulator (if equipped). Run engine at idle and check fuel pressure. If vehicle will not start, cycle key on and off several times. See FUEL PRESSURE SPECIFICATIONS  table. If fuel pressure is within specification, go to next step. If pressure is not to specification, remove fuel pressure gauge. Repair electric fuel pump or fuel pressure regulator.
2. Checking Fuel Pressure Check Valve. With KOEO, check that fuel pressure remains to specification for approximately 60 seconds. If system holds pressure, go to next step. If system does not hold pressure, go to step 6).
3. Fuel Delivery Test. Ensure fuel is of good quality. With key off, install fuel pressure gauge and pressurize fuel system as in step 1). Disconnect inertia switch. Crank engine for 5 seconds. If fuel pressure drop is greater than 5 psi after 5 seconds of cranking, the EEC-IV system is not the cause of the no start condition. Check additional DIAGNOSIS BY SYMPTOM tests. Reconnect inertia switch and remove fuel pressure gauge. If problem is rough running, missing, or a fuel service code, go to next step. If fuel pressure drop is less than 5 psi, remove fuel pressure gauge, reconnect inertia switch, and go to next step.
4. Checking Injector and Harness Resistance. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect pins for damage. Install breakout box, leave ECA disconnected, and set DVOM on 200-ohm scale. Measure resistance of injector banks between test pins No. 37 and 58 (bank No. 1) or 59 (bank No. 2) at breakout box. Record resistance. Refer to INJECTOR BANK RESISTANCE  table. If injector is within specification, go to step 6). If injector is not within specification, go to next step.
5. Isolating Faulty Injector Circuit. Turn key off. Install breakout box leaving ECA disconnected. Disconnect all injectors on suspect bank. With DVOM set on 200-ohm scale, connect one injector and measure resistance between test pins No. 37 and 58 or 59. Disconnect injector and repeat process for all other injectors. See INDIVIDUAL INJECTOR RESISTANCE  table for specifications. If injectors are within specifications, go to step 6). If injectors are not to specification, remove breakout box, reconnect ECA and injectors. Repair open/short in injector harness. If okay, replace injector. Rerun QUICK TEST.
6. Checking Injector Drive Signal. With key off and breakout box installed, connect ECA to breakout box. Using a non-powered 12 volt test light, connect test light between test pins No. 37 and 58 at the breakout box. Connect light between test pins No. 37 and 59 at the breakout box. Crank or start engine. A properly operating system will show a dim glow on test light. If light glows dim, go to next step. If test light does not come on, verify 12 volts at test pins No. 37 and 57. If test light glows bright, check injector circuit for shorts to ground. If okay, remove breakout box and replace ECA. Rerun QUICK TEST.
7. Fuel Pressure Problems: External Sources. Pressurize fuel system as per step 1). Visually inspect, fuel injector "O" rings, fuel pressure regulator, and fuel rails. If there is a visible leak, remove pressure gauge. Repair leak as necessary. Rerun QUICK TEST. If there is no leak, go to next step
8. Injector Balance Test. Connect tachometer to engine. Start and run engine at idle. Disconnect and reconnect injectors one at a time. Note RPM drop for each injector. Each injector should produce a momentary RPM drop of about 100 RPM drop. Note that ISC will attempt to re-establish correct RPM. If each injector does not produce at least 100 RPM drop when disconnected, service or 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.
9. This step procedure does not apply to trucks.
10. Service Code 41/91: Fuel Control Always Lean. If vehicle is equipped with dual HEGO's, Code 41 refers to the Right, or No. 1 HEGO and Code 91 refers to the Left, or No. 2 HEGO. Run engine at 2000 RPM for 2 minutes. Turn key off and wait 10 seconds. Rerun KOER SELF-TEST. Check for Code 41 or 91. If Code 41 or 91 is not displayed, go to step 19). If Code 41 and 91 is displayed, go to appropriate step number listed below.
    • Engines equipped with MAP sensors: Go to next step.
    • Engines equipped with VAF meters: Go to step 12).
    • Engines equipped with MA meters: Go to step 13).
11. Checking HEGO Sensor on Engines With MAP Sensors. Turn key off and set DVOM on 20-volt scale. Disconnect appropriate HEGO sensor from vehicle harness. Connect DVOM to HEGO SIGNAL lead at sensor and engine ground. Disconnect and plug vacuum line at MAP sensor. Apply 10-14 in. Hg vacuum to Manifold Absolute Pressure (MAP) sensor. Start engine and run engine at 2000 RPM for 2 minutes. If reading is less than 0.5 volt within 2 minutes, replace HEGO sensor(s) and then repeat QUICK TEST. If reading is greater than 0.5 volt within 2 minutes, go to step 14). If reading is less than 0.5 volt within 2 minutes, replace HEGO sensor, reconnect MAP, and rerun QUICK CHECK.
    NOTE: Vacuum or air leaks in non-EEC-IV related areas may cause Code 41 or 91. Check the following areas: A/C control motor, engine seals, EGR system, PCV system and lead contamination of HEGO sensor.
12. Checking HEGO Sensor on Engines With VAF meters. With key off and DVOM set on 20-volt scale, disconnect HEGO sensor from harness. Connect DVOM between HEGO SIGNAL at sensor and engine ground. Remove air cleaner in order to reach airflow meter inlet. Use a 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 volt within 2 minutes, replace HEGO sensor and repeat QUICK TEST. If reading is greater than 0.5 volt within 2 minutes, go to step 14).
13. Checking HEGO Sensor on Engines With MA Sensor. The purpose of this test is to verify HEGO sensor can generate a voltage signal of greater than 0.5 volt during KOER SELF-TEST. With key off and DVOM set on 20-volt scale, disconnect HEGO sensor from harness. Connect DVOM between HEGO SIGNAL at sensor and battery negative post. Rerun KOER SELF-TEST and monitor HEGO sensor voltage. If voltage is greater than 0.5 volt at end of SELF-TEST, go to next step. If voltage is less than 0.5 volt at end of SELF-TEST, replace HEGO sensor and rerun QUICK TEST.
14. Checking Continuity of HEGO Signal and Ground Circuits. Turn key off. Install breakout box, leaving ECA and HEGO disconnected. Set DVOM on 200-ohm scale and measure resistance between test pin No. 49 and battery negative post. Measure resistance between test pin No. 29 and HEGO SIGNAL at vehicle harness connector. For vehicles with dual HEGO sensors, measure resistance between test pin No. 43 and HEGO SIGNAL at vehicle harness connector. If all readings are greater than 5 ohms, repair open in appropriate circuit, connect HEGO sensor and ECA, and repeat QUICK TEST. If all readings are less than 5 ohms, go to next step.
15. Checking HEGO Circuit For Short to Ground. Turn key off. Leave breakout box installed and ECA disconnected. Disconnect HEGO sensor and set DVOM on 200K-ohm scale. Measure resistance between test pin No. 29 and test pin No. 40 at the breakout box. For vehicles with dual sensors measure resistance between test pin No. 43 and test pin No. 40. If any reading is less than 10K ohms, repair short to ground and repeat QUICK TEST. If reading is 10K ohms or more, go to next step.
16. Checking HEGO Sensor For Short to Ground. With key off, breakout box installed, and ECA disconnected, set DVOM to 200K-ohm scale. Disconnect HEGO sensor. Measure resistance between PWR GND and HEGO SIGNAL at the HEGO sensor connector. If resistance is less than 10K ohms, replace HEGO sensor and rerun QUICK TEST. If resistance is greater than 10K ohms, do the appropriate following procedure:
    • Engines equipped with MAP sensor: Go to next step.
    • Engines equipped with VAF meter: Go to step 18).
    • Engines equipped with MA (Mass Air Sensor): Remove breakout box, reconnect HEGO sensor, replace ECA and rerun QUICK TEST.
17. Eliminating Code 41: Engines With MAP Sensor. Turn key off. Install breakout box and connect ECA and HEGO sensor. Ensure MAP sensor vacuum hose is disconnected and plugged. Apply 10-14 in. Hg to MAP sensor. Start and run engine at 2000 RPM for 2 minutes. Allow engine to return 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. Return to step 1).
18. Eliminating Code 41: Engines With VAF Meter. With key off, install breakout box and connect ECA. Reconnect HEGO sensor. Remove air filter and insert a pencil in VAF meter inlet. Start engine and run at 2000 RPM for approximately 2 minutes. Rerun SELF-TEST. If Code 41 is not present, the HEGO circuit is okay, Remove breakout box, reconnect ECA and go to step 1) of this test. If Code 41 is displayed, remove test set-up, replace ECA, and rerun QUICK TEST.
19. Checking Resistance of HEGO Heating Element. Turn key off, disconnect HEGO sensor, and set DVOM on 200-ohm scale. Measure resistance between KEY POWER circuit and POWER GROUND circuit at HEGO connector. Hot-to-warm resistance should be 5-20 ohms. Room temperature resistance is 2-5 ohms. If resistance is within specification, go to next step. If resistance is not within specifications, replace HEGO sensor and rerun QUICK TEST.
20. Checking Power at HEGO Harness Connector. With KOEO, and HEGO disconnected, set DVOM on 20-volt scale. Measure voltage between KEY POWER circuit and POWER GROUND circuit at HEGO harness connector. If voltage is greater than 10.5 volts, HEGO system is okay, go to step 1) of this test. If voltage is less than 10.5 volts, go to next step.
21. Checking Continuity of Power Ground Circuit. Turn key off and wait 10 seconds. Disconnect HEGO sensor and set DVOM on 200-ohm scale. Measure resistance between POWER GROUND circuit at HEGO vehicle harness connector and battery negative post. If resistance is less than 5 ohms, repair open in KEY POWER circuit and rerun QUICK TEST. If resistance is more than 5 ohms, reconnect HEGO sensor and repair open in POWER GROUND circuit. Rerun QUICK TEST.
22. Service Code 42/92: Fuel Control Rich, Check HEGO SIGNAL For Short To Power. On dual HEGO systems, Code 42 refers to right side HEGO, Code 92 refers to left side HEGO. Turn key off and wait 10 seconds. Disconnect appropriate HEGO sensor. Set DVOM on 20-volt scale. With KOEO, measure voltage between HEGO SIGNAL and POWER GROUND at HEGO harness connector. If reading is more than .5 volt, repair short to power in HEGO circuit. Repeat QUICK TEST. If reading is less than 0.5 volt, go to next step.
23. Checking HEGO Sensor For Short to Key Power Circuit. Turn key off and leave HEGO disconnected. Set DVOM on 200K-ohm scale. Measure resistance from KEY POWER circuit to HEGO SIGNAL circuit at HEGO sensor connector. If reading is 10K ohms or less, replace HEGO sensor and repeat QUICK TEST. If reading is greater than 10K ohms, go to next step.
24. Attempt to Generate Code 41/91. The following non-EEC areas may cause these codes: fuel contaminated engine oil, ignition misfire and faulty CANP system. Turn key off and wait 10 seconds. Disconnect appropriate HEGO sensor. Using jumper wire, connect HEGO SIGNAL circuit at HEGO harness connector to battery negative terminal. Repeat KOER SELF-TEST. If Codes 41/91 are present, remove jumper wire and go to next step for engines with MAP. All others, go to step 27). If codes 41/91 are not present, remove jumper wire. Disconnect ECA connector and inspect for damage. If connector is okay, replace ECA. Repeat QUICK TEST.
    NOTE: Because the MAP sensor has a large influence on fuel control, a Code 42/92 may be the result of a faulty MAP sensor, even though a Code 22 has not been set. The next 2 test steps will verify the MAP vacuum circuit.
25. Checking MAP Sensor For Vacuum Leaks. 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.
26. Checking For Loss of Vacuum to MAP Sensor. 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 one in. Hg, inspect vacuum hoses for leaks, kinks, or blockage. Repair as required. If readings are within one in. Hg of each other, go to next step.
27. HEGO Sensor Check. Turn key off and wait 10 seconds. Disconnect HEGO sensor. Set DVOM on 20-volt scale and connect to HEGO SIGNAL at HEGO sensor connector and negative battery post. disconnect PCV valve hose to create a vacuum leak, which will cause the HEGO sensor to go lean. Start engine and run at 2000 RPM. The DVOM should indicate 0.4 volt within 30 seconds. If voltage is within specification, HEGO is okay, go to step 1) of this test. If voltage is not within specification, replace HEGO sensor and repeat QUICK TEST.
28. Continuous Memory Code 41 or 91. Indicates that a HEGO circuit has not switched during closed loop fuel control. In this situation a Code 41 or 91 may not indicate a lean condition. Diagnose all other driveability complaints in the DIAGNOSIS BY SYMPTOM test before attempting to service a Continuous Memory Code 41 or 91. Check the following areas.

    Unmetered Air/Vacuum Leaks

    • Canister Purge System
    • PVC System
    • Engine Sealing
    • Crimped Fuel Lines
    • Plugged Fuel Filter
    • Fouled Injectors

    HEGO Fuel Fouled

    • If an over-rich condition is suspected of fouling the HEGO sensor, run the vehicle at sustained high (legal) speeds followed by a few hard acceleration runs. This will allow the HEGO contamination to be burned off.

    Ignition System

    • Check for DEFAULT base timing in QUICK TEST procedure.

    Improper Fuel Used

    • Lead Fouled HEGO Sensor.

    Fuel Pressure

    • Check Pressure Using Steps 1) and 2).

    TP Sensor

    • With KOEO, move throttle slowly to WOT. Measure voltage between test pins No. 47 and 46 at breakout box. If voltage does not increase with throttle opening, replace TP sensor or linkage as necessary. If vehicle still has driveability problems, perform test steps 3) through 6).
29. Continuous Memory Codes 41, 42, 43, 65, 85 or 86. Diagnose all other driveability complaints before servicing these codes.
    • Code 41  - HEGO indication that the fuel system was lean for more than 15 seconds when the fuel system should have been in closed loop fuel control.
    • Code 42  - HEGO indication that the fuel system was rich for more than 15 seconds when the fuel system should have been in closed loop fuel control.
    • Code 43  - HEGO indicated that the fuel system was lean during WOT for more than 3 seconds.
    • Code 65  - Closed loop not activated on HEGO switching.
    • Code 85  - Excessive rich mixture condition corrected by adaptive fuel strategy.
    • Code 86  - Excessive lean fuel mixture condition corrected by adaptive fuel strategy.

    If an over-rich fuel condition is suspected or experienced, check ignition system. Burn off fuel deposits on HEGO by operating the vehicle at sustained high (legal) speeds followed by a few hard acceleration runs. This will allow the HEGO contamination to be burned off. Check the following areas:

    Code 41

    • Intermittent HEGO signal (Signal or Ground circuit).
    • If Code 65 also present, repair faulty HEGO circuit (Signal or Ground circuit).
    • If Code 43 also present, service Code 43 first.
    • Check VAF for leaks or sticking (caused by contamination or frost).
    • Low fuel pressure at WOT, check fuel supply.
    • Low fuel flow at WOT (pressure okay), check clogged injectors or low battery voltage.

    Code 42

    • Intermittent HEGO signal (Signal or Ground circuit).
    • Airflow meter indicating incorrect airflow, check for high voltage output due to sticking air vane ("flapper door").
    • Excessive fuel flow, pressure regulator vacuum supply disconnected or blocked fuel return line.
    • Excessive fuel flow, damaged or stuck open injector(s).

    Code 41 and 42

    • Intermittent HEGO signal (Signal or Ground circuit).
    • Sticking air vane ("flapper door"), due to contamination.
    • Contaminated HEGO sensor, lead or silicone fouled.

    Code 43

    • Low fuel pressure at WOT, fuel pump or restricted supply.
    • Low fuel flow at WOT, injectors plugged or low battery voltage (less than 11 volts). Code 65:
    • Check for faulty HEGO signal (Signal or Ground circuit).

    Code 85

    • If Code 42 also displayed, service it first.
    • Excessive fuel pressure, check regulator vacuum line and fuel supply line.
    • Excessive fuel flow, check for damaged injector pintles or injector stuck open.

    Code 86

    • If Code 41 also displayed, service it first.
    • Low fuel pressure, low pressure pump or restricted fuel supply.
    • Low fuel flow, clogged injectors or low battery voltage.