Test H - Fuel Control

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 (TESTS A TO X) 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 PROCEDURES . 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

INDIVIDUAL INJECTOR RESISTANCE

Engine

⁽¹⁾ Ohms

PFI & MA PFI

2.0-2.7

TBI

1.0-2.0

⁽¹⁾	Resistance values are for a single injector.

INJECTOR BANK RESISTANCE

Engine	Ohms
PFI & MA PFI	1.2-1.8

Fig 1: TBI Test Schematic

Fig 2: MA PFI Test Schematic

TEST PIN WIRE COLOR IDENTIFICATION

Application		Wire Color
Pin 29 (Right HEGO)		Tan/Orange
Pin 43 (Left HEGO)		Tan/Red
Pin 58
PFI		Tan/Red
All Others		Tan/Orange
Test Pin No. 59
PFI		Tan/Orange
All Others		Tan/Red

Fig 3: Test Schematic For All Other PFI Engines

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. For vehicles equipped with dual HEGO's Codes 41 and 42 refer to Right (rear) HEGO sensors. Codes 91 and 92 refer to Left (front) HEGO sensors.

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 9 for sequential PFI engines, or step 4 for all others. If vehicle is a no start, go to next step. If system does not hold pressure, go to step 6 for all engine applications except sequential PFI. For sequential PFI engines, go to step 9.
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 - EEC-IV 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. Do the following:
1. PFI ENGINES
  
  Measure resistance of injector banks between test pins No. 37 and 58 (Right or rear) or 59 (Left or front) at breakout box. Record resistance. Refer to INJECTOR BANK RESISTANCE table.
2. TBI ENGINES
  
  Measure resistance of injector circuit between test pins No. 37 and 58 at the breakout box. Record resistance.
Compare resistance with appropriate specification in INJECTOR BANK RESISTANCE table. If injector is within specification, go to step 6. If injector is not within specification, do the following:
1. PFI ENGINES
  
  Go to next step.
2. TBI ENGINES
  
  Remove breakout box and reconnect ECA. Repair open/short in harness/connector. If okay, replace injector. Rerun QUICK TEST PROCEDURES .
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 INDIVIDUAL INJECTOR RESISTANCE table 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 PROCEDURES .
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:
1. PFI ENGINES
  
  Connect test light between test pins No. 37 and 58 at the breakout box. Connect light between test pins No. 37 and 59 at breakout box.
2. TBI ENGINES
  
  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; except on sequential PFI engines. On sequential PFI engine, remove breakout box and reconnect ECA. Clean and test injectors. Rerun QUICK TEST PROCEDURES . If test light does not glow dimly, perform the following procedure:
1. No Light
  
  Check for 12 volts at test pins No. 37 and 57.
2. 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 procedures as applicable:
1. PFI ENGINES
  
  Visually inspect, fuel injector "O" rings, fuel pressure regulator, and fuel rails.
2. TBI ENGINES
  
  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 PROCEDURES . If there is no leak, go to next step for PFI engines. For TBI engines, 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.
8) Injector Balance Test (PFI only) 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. 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 PROCEDURES . 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, or HEGO ground. Check MAP frequency, etc.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 8) to step 11. No test procedures have been omitted.
11) Code 41 or 91: Fuel Control Always Lean If vehicle is equipped with dual HEGOs, Code 41 refers to the Right (rear) HEGO and Code 91 refers to the Left (front) 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 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.
- Engines equipped with MA meters: Go to step 14.
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 PROCEDURES .
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 4: 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 PROCEDURES . If reading is greater than 0.5 volt within 2 minutes, go to step 15.
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 5: Checking HEGO Sensor & Circuit
14) Check 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 and disconnect HEGO sensor from harness.
1. 4-WIRE HEGO SENSORS
  
  Connect DVOM between HEGO SIGNAL and HEGO GND at the HEGO sensor connector.
2. ALL OTHER HEGO SENSORS
  
  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 PROCEDURES .

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 6: 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 and use the following test:
1. TRUCKS WITH 4-WIRE HEGO
  
  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.
2. VEHICLES WITH DUAL HEGO SENSORS
  
  Measure resistance between test pin No. 43 at the breakout box and HEGO SIGNAL at the vehicle harness connector.
If all resistances are less than 5 ohms, go to next step. If not, repair open circuit. Remove breakout box, reconnect all components and repeat QUICK TEST PROCEDURES .

Fig 7: 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. For vehicles with dual sensors, measure resistance between test pin No. 43 and test pin No. 40. If any reading is less than 10 k/ohms, repair short to ground. Remove breakout box, reconnect all components and repeat QUICK TEST PROCEDURES . 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 PROCEDURES . 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.
- Engines equipped with MA (Mass Air Sensor): Remove breakout box, reconnect HEGO sensor, replace ECA and rerun QUICK TEST PROCEDURES .
Fig 8: 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 PROCEDURES .
If Code 41 is not present, remove breakout box and reconnect ECA and MAP sensor vacuum hose. HEGO input circuit is okay. On sequential PFI engines, fuel delivery is okay, fault is in an area common to all areas. Service as necessary. On all other engines 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 PROCEDURES .
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 PROCEDURES .

Fig 9: 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 (except sequential PFI engines). On vehicles equipped with sequential PFI engines, fuel delivery is okay, HEGO sensor may have cooled prior to KOER SELF-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 10: 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 PROCEDURES . 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 On dual HEGO systems, Code 42 refers to right (or rear) side HEGO, Code 92 refers to left (or front) 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 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 PROCEDURES . If reading is less than 0.5 volt, go to next step.

Fig 11: 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 PROCEDURES . 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 PROCEDURES .
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 PROCEDURES . 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.
1. PFI ENGINES
  
  Disconnect manifold vacuum hose as shown in this test step.
2. ALL MA PFI ENGINES
  
  Disconnect any vacuum hose from manifold vacuum tree fitting.
3. ALL OTHER ENGINES
  
  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 PROCEDURES . If voltage is to specification, HEGO sensor is okay. If engine has sequential PFI, fuel delivery is okay, problem is in an area common to all cylinders, such as a vacuum leak, fuel contamination, EGR system, MAP frequency, etc. Service as necessary. For all other engines, go to step 1 of this test.

Fig 12: Checking HEGO & Creating Vacuum Leaks on PFI
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 - EEC-IV article) before attempting to service a Continuous Memory Code 41 or 91. Check the following areas:
1. Circuits
  - HEGO SIG and GND circuits
  - HEGO harness insulation (near exhaust manifold)
2. Unmetered Air/Vacuum Leaks
  - Canister Purge (CANP) system
  - PCV system
  - Engine sealing
  - Crimped fuel lines
  - Plugged fuel filter
  - Fouled injectors
  - Air leaks between MAF and air outlet tube
3. 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.
4. Ignition System
  - Check for DEFAULT base timing in QUICK TEST PROCEDURES .
5. Improper Fuel Used
  - Lead fouled HEGO sensor.
6. Fuel Pressure
  - Check pressure using steps 1 and 2 of this test.
7. 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.
30) Continuous Memory Codes 41, 42, 43, 65, 85 or 86 Diagnose all other driveability complaints such as rough idle, missing, etc. before servicing these codes:
1. 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.
2. 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.
3. Code 43
  
  HEGO indicated that the fuel system was lean during WOT for more than 3 seconds.
4. Code 65
  
  Closed loop not activated on HEGO switching.
5. Code 85
  
  Excessive rich mixture condition corrected (made leaner) by adaptive fuel strategy.
6. Code 86
  
  Excessive lean fuel mixture condition corrected (made richer) 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:
1. Code 41:
  - Intermittent HEGO circuit (SIG or GND circuit).
  - If Code 65 also present, repair faulty HEGO circuit (SIG or GND 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.
2. Code 42:
  - Intermittent HEGO signal (SIG or GND circuit).
  - Vane Airflow (VAF) 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).
3. Codes 41 and 42:
  - Intermittent HEGO circuit (SIG or GND circuit).
  - Sticking VAF meter air vane (flapper door), due to contamination.
  - Contaminated HEGO sensor, lead or silicone fouled.
4. 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).
5. Code 65:
  - Check for faulty HEGO signal (Signal or Ground circuit).
6. 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.
7. 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.