AIR/FUEL RATIO CONTROL AND IGNITION SYSTEM Caterpillar

Air/Fuel Ratio Control System

Usage:

Influences On Engine Power

* Gas quality

* Engine settings

* Ignition advance

* Spark plugs

* Ambient temperature

* Gas supply

* Turbo boost pressure/waste gate control

Gas Pressure Leaks

1: Verify that the gas pressure at the regulator is 0.13 kPa (.5 inches of water) to 0.25 kPa (1.0 inch of water).

(1) Carburetor. (2) Deceleration fuel cutoff valve (DFCV). (3) Balance line. (4) Elbow. (5) Gas regulators or vaporizers.

a. Install the 8T0452 Water Manometer from the 1U5470 Engine Pressure Group in the balance line. Install 1/8 inch NPT fitting in the elbow (4) in the gas line before the DFCV (2).

b. Remove the balance line (3) from the carburetor (1) and install tee.

c. Connect the balance line to the tee.

d. Connect 8T0452 Water Manometer to the installed fittings.

e. Check gauge pressure reading.

Expected Result: Gas pressure at the regulator should be 0.13 kPa (.5 inches of water) to 0.25 kPa (1.0 inch of water).

Result:

* Gas Pressure Greater Than 0.25 kPa (1.0 inch of water).

Gas pressure regulator needs to be checked and adjusted if necessary. STOP.

* Gas Pressure Less Than 0.13 kPa (.5 inches of water).

Gas pressure regulator needs to be checked and adjusted if necessary. Proceed to next step.

2. Check for gas pressure leaks after the regulator.

a. Install a pressure gauge to the idle enrichment hose.

b. Check gauge pressure reading.

Expected Result: The gas pressure should be between 30 to 140 kPa (4 to 20 psi)

Result:

* Gas pressure is within the desired range.

Proceed to Continuity And Voltage Checks For Gas Shutoff Solenoid Valve (GSOV). STOP.

* Gas pressure is not within the range.

Proceed to next step.

3. Check voltage on the high pressure valve (OEM suppled).

a. Measure voltage on the high pressure valve coil to check if energizing when pressurizing.

Expected Result: The high pressure valve is energizing.

Result:

* The high pressure valve is energizing.

Proceed to next step.

* The high pressure valve is not energizing.

Repair or replace the high pressure valve if necessary. STOP.

4. Check restriction in the high pressure valve (OEM supplied).

a. Check for restrictions in the high pressure valve.

Expected Result: The high pressure valve has a restriction.

Result:

The high pressure valve has a restriction.

Remove restrictions. STOP.

The high pressure valve does not have a restriction.

Replace high pressure valve. STOP.

Continuity And Voltage Checks For The Gas Shutoff Solenoid Valve (GSOV).

1: Verify that the GSOV (OEM supplied) is receiving ground from the ECM.

NOTE: Refer to the OEM wiring diagram for checking power to the GSOV. The minimum voltage value may vary depending on the manufacturer.

a. Connect voltmeter to the GSOV.

b. Measure voltage on GSOV.

Expected Result: The GSOV is receiving a minimum of 10 volts.

Result:

* The GSOV is receiving 10 volts.

Proceed to next step.

* The GSOV is not receiving the 10 volts.

Continue troubleshooting, refer to OEM wiring diagram.

2: Check for restrictions in the filter.

a. Check for restrictions in the GSOV filter.

Expected Result: The GSOV filter has restriction.

Result:

* The GSOV filter has a restriction.

Remove restrictions. STOP.

* The GSOV filter does not have a restriction.

Proceed to next step.

3: Check for gas pressure towards pressure regulator.

a. Install a pressure gauge to the regulator side of the GSOV.

b. Check gauge pressure reading.

Expected Result: There is gas pressure towards the pressure regulator.

Result:

* There is gas pressure towards the pressure regulator.

Proceed to Stepper Motor (Engine Will Not Start).

* There is not gas pressure towards the pressure regulator.

Replace GSOV. STOP.

4: Check ECM for ground wire to the GSOV.

a. Remove the 37 pin connector from the ECM.

b. Verify that there is a pin in number 12.

Expected Result: The ECM provides the ground wire for the GSOV.

Result:

* The ECM provides the ground wire.

Proceed to next step.

* The frame provides the ground wire.

Inspect connections. Repair or replace wiring. STOP.

5: Check for continuity between ECM and GSOV.

a. Check wiring for loose connections, etc.

Expected Result: There is not continuity between ECM and GSOV.

Result:

* No continuity between ECM and GSOV.

Inspect connections. Repair or replace wiring. STOP.

* There is continuity between ECM and GSOV.

Replace ECM. Stop.

Stepper Motor (Engine Will Not Start)

1: Check for gas pressure up to the stepper motor valve.

a. Install 1/8 inch NPT fitting in the elbow in the gas line before the DFCV.

b. Remove the balance line from the carburetor and install tee.

c. Connect the 8T0452 Water Manometer from the 1U5470 Engine Pressure Group to the installed fittings.

d. Check gauge pressure reading.

Expected Result: The stepper motor valve has gas pressure.

Result:

* The stepper motor valve has gas pressure.

Proceed to next step.

* The stepper motor does not have gas pressure.

Check and adjust the gas pressure regulator. STOP.

2: Check wiring between the stepper motor and the ECM connector for continuity.

a. Check between air/fuel ratio control pins and ECM connector pins respectively for loose connections, etc.

Expected Result: There is continuity between ECM connector and stepper motor.

Result:

* Continuity between ECM connector and the stepper motor.

Proceed to next step.

* No continuity between ECM connector and the stepper motor.

Inspect connections. Repair or replace wiring. Stop.

3: Check for voltage from ECM.

a. Turn key to ON, engine OFF.

b. Check voltage between stepper motor pins A and B, C and D.

Expected Result: The voltage should be between 10 and 12 volts.

Result:

* Voltage is between 10 and 12 volts.

Proceed to next step.

* Voltage is not between 10 and 12 volts.

Replace ECM. STOP.

4: Check stepper motor for correct travel from bottom of stroke to top of stroke.

a. Remove stepper motor.

b. Hold the piston in place.

c. Turn ignition key to ON, engine OFF. The stepper motor goes through a self calibration by traveling to the bottom of the stroke and then to the top.

Expected Result: Stepper motor travels from top of stoke to the bottom.

Result(s):

* Stepper motor travels from top of stroke to the bottom.

Re-install stepper motor. Check and/or adjust gas pressure regulator. STOP.

* Stepper motor does not travel from top of stroke to bottom.

Replace stepper motor. STOP.

5: Check continuity between stepper motor valve and ECM

a. Check wiring for loose connections, etc.

Expected Result: Loss of continuity between stepper motor valve and ECM.

Result(s):

* No continuity between stepper motor valve and ECM.

Inspect connections. Repair or replace wiring. STOP.

* Continuity between stepper motor valve and ECM.

Replace stepper motor valve. STOP.

Starting The Engine

1: Check for a minimum of 9.5 volts while cranking.

a. Start the engine. Starting rpm is 125 to 250 rpm.

b. Check battery voltage while cranking.

Expected Result: Battery voltage is greater than 9.5 volts while cranking.

Result:

* Voltage is greater than 9.5 volts while cranking.

Proceed to next step.

* Voltage is less than 9.5 volts while cranking.

Charge and/or replace the batteries. STOP.

2: Check ECM for rpm signal from the monitoring software.

a. Hook up the monitoring software.

b. Check display for speed, stepper motor steps, flags and fault codes.

Expected Result: Values displayed.

Result:

* Values not displayed.

Proceed to next step.

* Values displayed.

Proceed to Deceleration Fuel Cutoff Valve.

3: Check for voltage from the ignition system

a. Check for voltage (160 VDC) between pin G of the ignition system and pin 22 of the ECM.

Expected Result: There is 160 VDC between ECM and the ignition system.

Result:

* Voltage is 160 VDC.

Proceed to next step.

* Voltage is not 160 VDC.

Proceed to Ignition Systems.

4: Check continuity between ECM and ignition system.

a. Check wiring for loose connections, etc.

Expected Result: Loss of continuity from ECM and ignition system.

Result:

* No continuity between ECM and ignition system.

Inspect connections. Repair or replace wiring. STOP.

* Continuity between ECM and ignition system.

Replace ECM. STOP.

Fault Code 43 - Main Fuel DFCV Valve Not Operating

During DFCV operation, the fuel is shut off. If the mixture becomes excessively lean, a fault code will be activated. If the mixture does not become lean during deceleration check if air pressure is applied to the DFCV.

With the vehicle being driven, the following conditions need to occur for the DFCV to shut off fuel to the engine:

* Accelerator is released and

* Engine rpm remains at a high level and

* Manifold pressure remains at a low level.

Hook up the monitoring software to access the control flags. The control flags tell if the DFCS and the DFCV are being activated. Under control flag 1 = 1000000, the control breaks the ground wire C211 to the DFCS. This de-activates the DFCS applying air pressure to the DFCV cutting off the fuel to the engine.

NOTE: This control flag is for confirmation that the DFCS is to be activated. This control flag does not mean the DFCS or the DFCV is working properly.

NOTE: The DFCV will not operate properly if there is not a signal from the ignition system. Refer to Starting The Engine, STEP 3, for more information.

1: Check for air pressure cutoff to the DFCV.

a. Check for air pressure to the DFCV.

Expected Result: There is air pressure to the DFCV.

Result:

* Air pressure to the DFCV.

Proceed to next step.

* No air pressure to the DFCV.

Check Tank for low air pressure and DFCS wiring. Repeat steps 1. If there still is not any air pressure then replace the DFCS. STOP.

2: Check for air pressure to the DFCV.

a. Key on. Engine stopped.

b. Check air pressure to the DFCV.

Expected Result: Air pressure to the DFCV.

Result:

* Air pressure to the DFCV.

Proceed to next step.

* No air pressure to DFCV.

Replace the DFCS. STOP.

3: Check voltage of Deceleration Fuel Cutoff Solenoid (DFCS).

a. Check the voltage from C212 to chassis ground and from C211 to chassis ground.

Expected Result: Voltage is less than 10 volts.

Result:

* Voltage is less than 10 volts for C211.

Proceed to next step.

* Voltage is not less than 10 volts for C212.

Proceed to next STEP 5.

4: Check wire C211 for continuity with the ECM.

a. Check for loose connections, etc. between C211 and pin 13 of the ECM.

Expected Result: No continuity between C211 and pin 13 of the ECM.

Result:

* No continuity between C211 and pin 13 of the ECM.

Check connections. Repair or replace wiring. STOP.

* Continuity between C211 and pin 13 of the ECM.

Replace ECM. STOP.

5: Check wire 212 for continuity with the ECM.

a. Check for loose connections, etc. between C212 and pin 6 of the ECM.

Expected Result: No continuity between C212 and pin 6 of the ECM.

Result:

* No continuity between C212 and pin 6 of the ECM.

Repair and/or replace wiring. STOP.

* Continuity between C212 and pin 6 of the ECM.

Replace 7.5 amp fuse (PC2). STOP.

Oxygen Sensor

1: Check if "Closed Loop".

a. Hook up monitoring software.

b. Check display screen.

Expected Result: Is "Closed Loop" displayed?

Result(s):

* Not a closed loop system.

Proceed to next step.

* Closed loop system.

Proceed to Adjusting Fuel for Proper AFRC.

2: Check if "Pre-heated".

a. Hook up monitoring software.

b. Check display screen.

Expected Result: "Pre-heated" is not displayed.

Result:

* "Pre-heat" is not displayed.

Proceed to next step.

* "Pre-heat" is displayed.

Proceed to STEP 5.

3: Check gas mixture.

a. Start Engine.

b. Check voltage between S582(gray) and S583(black).

NOTE: A lean mixture is 100 to 300 mV, a normal mixture is 400 to 600 mV, and a rich mixture is 800 to 1000 mV.

Expected Result: Mixture is not rich or lean.

Result:

* Mixture is not rich or lean.

Proceed to next step.

* Mixture is rich or lean.

Proceed to MAPS, IMTS, Sensors.

4: Check wiring.

a. Check for Fault Code 13 - Oxygen Sensor No Signal.

b. check for loose connections, etc.

Expected Result: No continuity.

Result:

* No continuity.

Check connections. Repair or replace wiring if necessary. STOP.

* Continuity.

Replace Oxygen Sensor. STOP.

5: Check continuity between oxygen sensor and ECM.

a. Check between oxygen sensor control pins and ECM connector pins respectively for loose connections, etc.

Expected Result: No continuity.

Result:

* No continuity.

Repair or replace wiring if necessary.

* Continuity.

Proceed to next step.

6: Check heater voltage.

a. Turn key On, engine off.

b. Check voltage between S580(white) and S581(white).

Expected result: No voltage.

Result:

* No voltage.

Replace ECM. STOP.

* Voltage.

Go back to STEP 3.

7: Check oxygen sensor voltage.

a. Check voltage of sensor between S582(gray) and S583(black).

Expected Result: 450 mV constant voltage.

Result(s):

* 450 mV constant voltage.:

Replace the oxygen sensor. STOP.

* Voltage varies.

Proceed to next step.

Maps, IMTS And Sensors

Fault Code 33 - Map High Fault Code 34 - Map Low Fault Code 23 - Mat Sensor Low Fault Code 13 - Oxygen Sensor No Signal.

1: Check if "Closed Loop".

a. Hook up monitoring software.

b. Check display screen.

Expected Result: "Closed loop" displayed.

Result:

* "Closed loop" displayed.

Proceed to Adjusting Fuel For Proper AFRC.

* "Closed loop" not displayed.

Proceed to next step.

2: Check for faults.

a. Hook up monitoring software.

b. Check display screen.

Expected Result: No faults.

Result:

* No faults.

Proceed to next step.

* Faults.

Proceed to Fault Codes.

3: Check continuity between ECM, Sensors, and Caterpillar Module Interface (CMI)

a. Check CMI control pins with MAP and IMTS pins.

b. Check ECM pins with MAP and IMTS pins.

Expected Result: Continuity.

Result:

* Continuity.

Proceed to next step.

* No continuity.

Check connections. Repair or replace wiring if necessary. STOP.

4: Check output voltage of MAP, IMT sensors.

a. Check voltage of MAP sensor pin C to pin B.

b. Check voltage of IMT sensor pin C to pin B.

Expected Result: No output voltage.

Result:

* No output voltage.

Replace the appropriate sensor. STOP.

* Output voltage.

Replace the ECM.

Adjusting Fuel For Proper Air/Fuel Mixture

Check stepper motor for correct movement.

a. Hook up the software monitoring system to the ECM.

b. Engage the parking brake.

c. Key ON, engine ON with the engine in park/neutral, idle the engine.

d. Record the motor position.

e. Record the C/L readings.

f. Press and hold the accelerator down several times.

g. Allow the engine to return to idle.

h. Record the motor position.

i. Record the C/L readings.

Expected Result: Not the same motor position.

Result:

* Not the same motor position.

Proceed to next step.

* The same motor position.

No adjustment needed. STOP.

2: Check Mixture.

a. Record C/L readings with the engine at 750 rpm.

NOTE: A positive correction number means the mixture is lean. A negative correction number means the mixture is rich.

Expected Result: The C/L reading is greater than ± 20.

Result:

* The C/L reading is greater than ± 20.

Proceed to next step.

* The C/L reading is within ± 20.

Proceed to Run Stall Speed Check.

3: Adjust Pressure Regulator.

a. If the C/L reading is greater than 20 then turn the adjusting tower screw counterclockwise until the C/L reading is less than 20.

b. If the C/L reading is less than -20 then turn the adjusting tower screw clockwise until the C/L reading is greater than 20.

STOP.

Run Stall Speed Check (Automatic Only)

1: Check Engine RPM.

a. Engage the parking brake.

b. Press on the service brake pedal.

c. Start engine.

d. Place transmission in drive.

e. Accelerate the throttle to the floor.

f. Record the rpm reading.

Expected Result: RPM is not within 1450 to 1600 rpm.

Result:

* RPM is not within 1450 to 1600 rpm.

Proceed to next step.

* RPM is within 1450 to 1600 rpm.

Proceed to Deceleration Fuel Cutoff Valve (DFCV).

2: Check mixture.

a. Hook up monitoring software.

b. Check display for C/L readings.

NOTE: An air leak in the regulator adjustment screw tower, fittings, hoses will cause the stepper motor and mV readings to vary from very rich 900 to 1000 mV, to very lean 0 to 100 mV. There will also be a 100 to 150 rpm surge.

Expected Result: The C/L reading is within ± 20.

Result:

* The C/L reading is within ± 20.

Proceed to next step.

* The C/L reading is not within ± 20.

Turn the stepper motor valve's main adjusting screw until the C/L reading is within ± 20. STOP.

3. Check minimum values.

a. Check gas flow.

b. Check gas quality.

c. Check gas pressure.

Expected Result: Values are within minimum limits.

Result:

* Values are within minimum limits.

Proceed to next step.

* Values are not within limits.

Proceed to troubleshooting Fault Codes.

4: Check stepper motor valve.

a. Check C/L readings to see if mixture remains constantly rich or lean.

b. Check Stepper motor valve to see if it is moving far open or far closed.

Expected Result: Mixture is constantly rich/lean.

Result:

* Mixture is constantly rich/lean.

Replace the stepper motor. STOP.

* Mixture is not constantly rich/lean.

Check oxygen sensor and air/fuel ratio control. STOP.

Fault Codes.

A fault code can effect the control but will not shut down the system completely. The diagnostic codes are called malflags on the software monitoring software. These fault codes are helpful in troubleshooting which system or component has failed. ANY FAULT CODE MUST BE SOLVED BEFORE CONTINUING.

1: Display fault codes.

a. Hook up software monitoring system.

b. Turn ignition ON, start engine.

c. Select "Diagnost" from the menu. This will display the fault code(s).

NOTE: A fault code can be reset by disconnecting the power supply. Remove the 37 pin connector on the ECM or disconnect the battery.