Test H - Fuel Control: Notes

NOTE: For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article.

NOTE: Perform this test when Code 41, 91, 42, 92, 43, 65, 85, 86 or 93 is displayed during QUICK TESTS or when directed here by other test procedures.

NOTE: See HOW TO USE CIRCUIT TESTS, at beginning of circuit tests before performing this test. Fuel contaminated engine oil may affect Codes 41, 91, 42, or 92. If this is suspected, remove PCV valve from valve cover and repeat QUICK TEST. If problem is corrected, change engine oil and filter.

NOTE: Use this test to diagnose only the following components:

HEGO sensor
HEGO signal and ground circuit
HEGO sensor connection
Vacuum systems
Fuel injector
ECA
Electrical circuits (HEGO GND, HEGO, INJ 1-8, VPWR and SIG RTN)
NOTE: To prevent replacement of good components, be aware of the following non-EEC areas which may be the cause of driveability concerns:
Ignition coil, distributor cap or rotor
Faulty or fouled spark plugs or wires
Faulty CANP system
Distributorless Ignition System (DIS)
EGR valve and gasket
Air filter
Fuel or engine oil contamination
Poor electrical ground
Faulty fuel pressure
Intake or exhaust system leaks
Engine below normal operating temperature

CAR - INDIVIDUAL INJECTOR RESISTANCE ⁽¹⁾

Engine

Ohms

2.5L CFI

1.0-2.0

⁽¹⁾	Resistance values are for a single injector.

Fig 1: 2.5L CFI Test Schematic

TEST PIN WIRE COLOR IDENTIFICATION

Application	Wire Color
Pin 29 (Right HEGO): 2.5L CFI	Tan/Orange
Pin 43 (Left HEGO): 2.5L CFI	Tan/Red
Pin 58: 2.5L CFI	Tan/Orange
Test Pin No. 59: 2.5L CFI	Tan/Red

NOTE: KOER Codes 41 and 91 are HEGO codes that indicate the system is always lean. KOER Codes 42 and 92 indicate the system is always rich.

1) Check Fuel Pressure Turn ignition key off and 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. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If vehicle is a no start, cycle key on and off several times. 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) Check Fuel Pressure Check Valve With KOEO, ensure that fuel pressure remains within specification for approximately 60 seconds. If system holds pressure, but vehicle runs rough or misses, or Codes 41, 42, 91 or 92 are present, go to step 4). If vehicle is a no start, 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 no start tests in TESTS W/O CODES article. If fuel pressure drop is less than 5 psi, remove fuel pressure gauge, reconnect inertia switch, and go to next step.

4) Check Injector & Harness Resistance Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect pins for damage. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance of injector circuit between test pins No. 37 and 58 at the breakout box. Record resistance. Compare resistance with appropriate specification in appropriate INJECTOR BANK RESISTANCE table. If injector is within specification, go to step 6). If injector is not within specification, remove breakout box and reconnect ECA. Repair open/short in harness/connector. If okay, replace injector. Rerun QUICK TEST.

5) Isolate Faulty Injector Circuit Turn key off. Install breakout box and disconnect ECA. 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 appropriate INDIVIDUAL INJECTOR RESISTANCE for specifications. If all injectors are within specifications, go to step 6). If injectors are not to specification, remove breakout box, reconnect ECA and injectors. Repair open or short in injector harness. If circuit is okay, replace injector. Rerun QUICK TEST.

6) Check Injector Drive Signal With key off and breakout box installed, connect ECA to breakout box. Use a non-powered 12-volt test light and the following connection procedure. Connect test light between test pins No. 37 and 58 at the breakout box.

Crank or start engine. A properly operating system is indicated by a test light that glows dimly. If light glows dimly, go to next step. If test light does not glow dimly, perform the following procedure:

No Light - Check for 12 volts at test pins No. 37 and 57.
Bright Light - Check injector circuit for shorts to ground. If system is okay, remove breakout box and replace ECA. Remove breakout box, reconnect all components and repeat QUICK TEST.

7) Fuel Pressure Problems: External Sources Pressurize fuel system as per procedure in step 1) of this test. Examine fuel system using the following procedure. Remove air inlet duct at fuel charging assembly injection inlet. Visually inspect, fuel injector "O" rings, fuel pressure regulator and fuel line connections.

If there is a visible leak, remove pressure gauge. Repair leak as necessary. Rerun QUICK TEST. If there is no leak, remove pressure gauge. Fuel delivery system is okay. Problem is in common area for all cylinders, such as, vacuum leak, fuel contamination, or EGR leak.

NOTE: There is a break in the step numbering sequence at this point, skipping from step 7) to step 11). Break is due to previous chart references to these testing procedures. No test procedures have been omitted.

11) Code 41 or 91: Fuel Control Always Lean 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 20). If Code 41 or 91 is displayed, go to appropriate step number as listed below.

Engines equipped with MAP sensors: Go to next step.
Engines equipped with VAF meters: Go to step 13).

12) 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. Apply 10-14 in Hg to Manifold Absolute Pressure (MAP) sensor and start engine. Run engine at 2000 RPM for 2 minutes. If reading is greater than 0.5 volt, go to step 15). If reading is less than 0.5 volt, replace HEGO sensor, reconnect MAP, and rerun QUICK TEST.

NOTE: Vacuum or air leaks in non-EEC-IV related areas may cause Code 41 or 91. Check the following areas: leaking vacuum actuator (A/C control motor, etc.) engine seals, EGR system, PCV system and lead contamination of HEGO sensor.

Fig 2: Checking HEGO Sensor

13) Check HEGO Sensor on Engines With VAF Meters With key off and DVOM set on 20-volt scale, disconnect HEGO sensor from vehicle harness. Connect DVOM between HEGO SIGNAL at sensor connector 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, remove pencil from VAF meter and repeat QUICK TEST. If reading is greater than 0.5 volt within 2 minutes, go to step 15).

Fig 3: Checking HEGO Sensor & Circuit

NOTE: There is a break in the step numbering sequence at this point, skipping from step 13) to step 15). Break is due to previous chart references to these testing procedures. No test procedures have been omitted.

Connect DVOM to HEGO SIGNAL at the sensor and battery negative post. Rerun KOER Self-Test and monitor HEGO sensor voltage. If voltage is greater than 0.5 volt, go to next step. If voltage is less than 0.5 volt, replace HEGO sensor and rerun QUICK TEST.

Fig 4: Checking HEGO Sensor

15) Check Continuity of HEGO SIGNAL & POWER GROUND Circuits Turn key off. Install breakout box, leaving ECA and HEGO disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pin No. 49 at the breakout box and battery negative terminal. Measure resistance between test pin No. 29 at the breakout box and HEGO SIGNAL at the vehicle harness connector.

Fig 5: HEGO Sensor Connector

16) Check HEGO Circuit For Short to Ground Turn key off. Leave breakout box installed and ECA disconnected. Disconnect HEGO sensor and set DVOM on 200-k/ohm scale. Measure resistance between test pin No. 29 and test pins No. 40 and 49 at the breakout box. If any reading is less than 10 k/ohms, repair short to ground. Remove breakout box, reconnect all components and repeat QUICK TEST. If reading is 10 k/ohms or more, go to next step.

17) Check HEGO Sensor For Short to Ground With key off, breakout box installed, and ECA disconnected, set DVOM to 200-k/ohm scale. Disconnect HEGO sensor. Measure resistance between PWR GND and HEGO SIGNAL at the HEGO sensor connector. If resistance is less than 10 k/ohms, replace HEGO sensor, remove breakout box, reconnect all components and repeat QUICK TEST. If resistance is greater than 10 k/ohms, go to the appropriate following procedure.

Engines equipped with MAP sensor: Go to next step.
Engines equipped with VAF meter: Go to step 19).

Fig 6: Checking HEGO Sensor

18) Attempt to Eliminate Code 41: Engines With MAP Sensor Turn key off. Install breakout box and reconnect ECA and HEGO sensor. Ensure MAP sensor vacuum hose is disconnected and plugged. Start and run engine at 2000 RPM for 2 minutes. Allow engine to return to idle. Apply 10-14 in. Hg to MAP sensor. Perform KOER Self-Test. If Code 41 is still present, remove breakout box. Reconnect ECA and MAP sensor vacuum line. If engine still runs rough, go to TEST S, step 2). If not, replace ECA and repeat QUICK TEST.

If Code 41 is not present, remove breakout box and reconnect ECA and MAP sensor vacuum hose. HEGO input circuit is okay. Return to step 1) of this test.

19) Attempt to Eliminate Code 41 on 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 to hold air door open. Start engine and run at 2000 RPM for approximately 2 minutes. Rerun KOER 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, remove breakout box, reconnect components and repeat QUICK TEST.

20) Check Resistance of HEGO Heating Element Turn key off, disconnect HEGO sensor, and set DVOM on 200-ohm scale. Measure resistance between KPWR circuit and PWR GND circuit at HEGO sensor connector. Hot to warm resistance should be 5.0-25.0 ohms. Room temperature resistance is 2.0-5.0 ohms. If resistance is within specification, go to next step. If not, replace HEGO sensor, and repeat QUICK TEST.

Fig 7: Checking HEGO Sensor

21) Check For Power at HEGO Harness Connector With KOEO, and HEGO disconnected, set DVOM on 20-volt scale. Measure voltage between KEY POWER circuit and PWR GND circuit at HEGO vehicle harness connector. If voltage is greater than 10.5 volts, HEGO system is okay, go to step 1) of this test. If a driveability symptom persists, fault is in an area common to all cylinders such as air or vacuum leaks, fuel contamination, EGR, MAP, etc. For all vehicles, if voltage is less than 10.5 volts, go to next step.

Fig 8: HEGO Sensor Connector

22) Check 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 PWR GND circuit at HEGO vehicle harness connector and battery negative post. If resistance is less than 5 ohms, repair open in KEY POWER circuit. Reconnect HEGO and rerun QUICK TEST. If resistance is more than 5 ohms, reconnect HEGO sensor and repair open in PWR GND circuit. Reconnect HEGO sensor and rerun QUICK TEST.

23) Code 42 or 92: Fuel Control Always Rich, Check HEGO SIGNAL For Short To Power Disconnect appropriate HEGO sensor. Set DVOM on 20-volt scale. With KOEO, measure voltage between HEGO SIG and PWR GND at HEGO vehicle harness connector. If reading is more than .5 volt, repair short to power in HEGO circuit. Reconnect HEGO sensor and repeat QUICK TEST. If reading is less than 0.5 volt, go to next step.

Fig 9: HEGO Sensor Connector

24) Check HEGO Sensor For Short to KPWR Circuit Turn key off. Disconnect HEGO sensor. Set DVOM on 200-k/ohm scale. Measure resistance from KPWR circuit to HEGO SIG circuit at HEGO sensor connector. If reading is 10 k/ohms or less, replace HEGO sensor and repeat QUICK TEST. If reading is greater than 10 k/ohms, go to next step.

25) Attempt to Generate Code 41 or 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 SIG circuit at HEGO vehicle harness connector to battery negative terminal. Repeat KOER Self-Test. If Code 41 or 91 is present, remove jumper wire and go to next step for engines with MAP. For all other engines, go to step 28). If Codes 41 and 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 MAP sensor has a large influence on fuel control, a Code 42 or 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.

26) Check 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 to MAP sensor. If sensor does not hold vacuum, replace MAP sensor. Remove vacuum pump. Connect vacuum hose and reconnect HEGO. Repeat QUICK TEST. If MAP holds vacuum, release vacuum and go to next step.

27) Check 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 at a stable idle. 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 1 in. Hg, inspect vacuum hoses for leaks, kinks, or blockage. Repair as necessary. If readings are within 1 in. Hg of each other, go to next step.

28) 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 battery negative post. Remove a vacuum hose to create a vacuum leak, which will cause the HEGO sensor to go lean. Disconnect the PCV valve hose from the PCV valve. Start engine and run at approximately 2000 RPM. DVOM should indicate less than 0.4 volt within 30 seconds. If not, replace HEGO sensor. Reconnect vacuum hoses and repeat QUICK TEST. If voltage is to specification, HEGO sensor is okay. Go to step 1) of this test.

29) Continuous Memory Code 41 or 91 (With Exhaust Odor or Smoke) Codes 41 or 91 indicate 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 (see SYMPTOMS in TESTS W/O CODES article) before attempting to service a Continuous Memory Code 41 or 91. Check the following areas: