Troubleshooting Fuel Systems on 3126B Marine Engines{1000} Caterpillar

Engine:

3126B (S/N: 9ZF1-UP; 3GS1-UP)

Introduction

This publication provides some basic troubleshooting procedures for the fuel system on 3126B Marine Engines. Use the procedures that are found within this special instruction in order to troubleshoot low power complaints before submitting warranty claims. The procedures will help to properly diagnose problems with the injectors and problems with the Hydraulic Electronic Unit Injector (HEUI) pump. Before submitting warranty claims for sets of injectors, data from a sea trial must be entered into the "Sea Trial Database". Data from the "Cylinder Cut Out Test" is required before replacing the set of injectors. If the HEUI pump is being replaced, Special Instruction, REHS1281, "Procedure for Diagnosing the HEUI Fuel System" is required.

Troubleshooting with Caterpillar Electronic Technician (ET)

1. Verify that the low power complaint is not due to a programmed parameter. If a 268-02 Check Programmable Parameters is present in the fault codes, verify that all of the system and customer parameters have been correctly programmed. Refer to Special Instruction, REHS1187, "Electronic Installation Guide" as a reference guide.

2. Monitor the Cat ET status screen in order to verify that the engine exits cold mode (1). If the engine is in cold mode (1), allow the engine to warm up and exit cold mode (1). Verify that the "troll mode" function is not enabled. Refer to Illustration 1.

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Illustration 1	g01076180
(1) Cold mode

3. With the Cat ET service tool, check for active derates (2) and fault codes. Refer to Illustration 2. Derates (2) and fault codes can be generated because of low pressures or high temperatures. Also, verify that the "Customer Specified Monitoring Parameters" have not been programmed out of the normal operating range.

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Illustration 2	g01076181
(2) Engine derate

4. With the Cat ET service tool, check the throttle input signal to the Electronic Control Module (ECM). Verify that the throttle duty cycle is within the range of 5 percent (low idle) to 95 percent (high idle).

5. Verify that the air inlet heater is not energized after the engine has left cold mode.

6. Verify that the engine oil level is correct. Start the engine. Allow the engine to reach operating temperature. Perform a "Cylinder Cut Out Test" three times. Review the results. If failure of an injector is not identified, perform three "Cylinder Cut Out Tests" under moderate load at 1600 RPM. Compare the results.

Checking the Fuel Supply

1. Verify that the engine has the correct size of fuel supply and fuel return lines. Refer to Marine Application and Installation Guide, LEKM7147.

2. Check for restricted fuel lines, collapsed fuel lines, or pinched fuel lines.

3. Check the fuel filter for plugging. If the condition of the fuel filter is questionable, replace the fuel filter.

4. Remove the hand priming pump and inspect the check valves for proper operation. Reinstall the hand priming pump after verifying that the pump is operating correctly. If the condition of the hand priming pump is questionable, the hand priming pump can be replaced with the 6N-4414 Filter Base Cover .

5. Install sight glasses in the fuel supply and fuel return lines. Monitor the fuel lines for air in the fuel.

6. Verify that the temperature of the fuel supply does not exceed a maximum of 38 °C (100 °F). Fuel supply temperatures that are above 38 °C (100 °F) will result in a loss of power. The loss of power will be one percent for each 6 °C (10 °F) above 38 °C (100 °F). The life of the injectors will also decrease if the fuel temperature exceeds 66 °C (150 °F).

7. Check the specific gravity of the fuel in order to determine the density of the fuel. The minimum specific gravity is 33 API. The maximum specific gravity is 37 API. The optimum specific gravity is 35 API. The values of specific gravity are corrected to 60 °F.

Checking the Lubrication System

1. Check the oil level in the crankcase of the engine.

2. Verify that the correct viscosity of oil is being used in the engine.

3. Collect an oil sample in a clear bottle. Ensure that there are no air bubbles or entrapped air in the sample.

Checking the Inlet and Exhaust System

1. Measure the air inlet restriction at the air cleaner. Compare the measurement to the specification that is provided in the Technical Marketing Information (TMI).

2. Check the inlet air temperature at the air cleaner. The maximum inlet air temperature for Caterpillar engines is 49 °C (120 °F).

3. Verify that the exhaust restriction is within the specifications that are provided in the TMI.

4. Check the aftercooler core for plugging.

5. Verify that the boost pressure sensor is functioning properly. Check for active sensor faults. Verify that the pressure that is read by the ECM is correct. Verify the pressure with a manual gauge that has been calibrated. Ensure that the boost pressure sensor reads zero when the engine is off and the key is in the on position.

Troubleshooting the Injectors

1. Check for active fault codes or logged fault codes for the injectors.

2. Verify that the engine is properly filled with the correct viscosity of oil.

3. Perform a "Cylinder Cut Out Test" with the engine at operating temperature and at low idle. Also run the test with a moderate load. A significant deviation in the fuel position indicates a cylinder that has a problem.

4. Check the injector wiring harness and perform the "Injector Solenoid Test". Check for an open circuit between the injector harness and the ECM.

5. If a faulty injector can not be identified, perform a sea trial. Refer to General Service Information, LEBV4830, "Marine Analyst Service Handbook". The sea trial will aid in determining if the engine is burning the correct amount of fuel. The sea trial will also aid in determining if the engine is producing the correct amount of boost and the correct exhaust temperatures.

6. When a set of injectors is removed, use a borescope in order to verify that a distinct crosshatch pattern exists in the cylinder liner. Verify that no rust exists. Also, inspect the valve seats and valve faces.

HEUI Pump Troubleshooting

If the engine will not start, the following items are possible causes. Also, refer to Special Instruction, REHS1281, "Procedure for Diagnosing the HEUI Fuel System".

1. The drive gear is inadequately torqued in order to engage the gear and the shaft.

2. The Injection Actuation Pressure Control Valve (IAPCV) has malfunctioned and the IAPCV will not allow the pump to build pressure.

3. The HEUI pump has an internal malfunction.

Instability of engine speed can be caused by erratic rail pressure.

1. Check the diagnostic codes on the engine in order to verify that a 164-11 Injector Actuation Pressure system fault has not occurred. A 164-11 diagnostic code indicates that the desired injection pressure and the actual injection pressure are not equal.

2. In order to verify the 164-11 code, complete a data log in Cat ET and record the following items: "Engine Speed", "Desired Injection Actuation Pressure", "Actual Injection Actuation Pressure" and "Injection Actuation Current". Review the data and verify that the actual injection actuation pressure is within 3 MPa (435 psi) of the desired injection actuation pressure while the engine is running.

3. If a 164-11 Injector Actuation Pressure system fault occurs, or if the actual injection actuation pressure varies by more than 3 MPa (435 psi), replace the IAPCV.

Performing a Sea Trial

It is important to connect calibrated gauges in order to measure fuel flow when a sea trial is performed in order to diagnose low power. The "Fuel Flow" parameter in Cat ET is a calculation of fuel flow. The parameter in Cat ET is not an actual measurement. The ECM will signal the injector to deliver fuel. If the injector malfunctions, the injector may not deliver the fuel that is required. Exhaust temperatures are also very important in determining a low power complaint. An outline of a procedure for a sea trial can be found below. Also, refer to Sea Trial Guide for Marine Engines, LEBM5081.

There are three steps that must be completed on the vessel in order to conduct a thorough sea trial. The "General Information", the "Sea Trial Transient", and the "Sea Trial Steady State test" must be completed. All three functions are completed with Cat ET. These functions must be done while Cat ET is connected to the engine and while the ECM is powered. The "General Information" file contains the following information:

• "Vessel name"

• "Port"

• "Customer name"

• "Builder"

• "Dealer information"

• "Hull Type"

• "Lengths"

• "Weights"

• "Capacities"

• "Vessel type"

• "Engine model" and "transmission model"

• "Engine serial number" and "transmission serial number"

• "Arrangement numbers"

• "Gear ratio's"

• "Engine personality module indentification"

• Data that is taken before the sea trial, including "Fuel API", "sea water temperature", "ambient temperature", and "sea water conditions"

• "Comments" field

Note: In order to complete the "General Information" file, the laptop computer must be connected to the ECM and the ECM must be powered.

1. After completing the "General Information" file, the vessel should be operated until all of the engine related systems are at normal operating conditions.

2. Once the vessel is at sea, the engines should be warmed up to operating temperature and the door to the engine room should be closed.

3. Ensure that the throttles are synchronized. Also, fully raise the trim tabs.

4. Initialize the "Sea Trial Transient" recorder and construct channel groups with the following channels.
   • "Engine speed"

   • "Desired engine speed"

   • "Rated fuel limit"

   • "Fuel position"

   • "Fuel ratio control (FRC) limit"

   • "Fuel rate"

   • "Injection actuation pressure"

   • "Desired injection actuation pressure"

   • "Boost pressure"

   • Manual channels: "Fuel consumption" recorded with the calibrated gauges, "Fuel pressure" recorded with the calibrated gauge and "Exhaust temperature" before the turbocharger

5. Once these groups have been added, make sure that the "recorder acquisition time" is set for a sufficient amount of time. A "recorder acquisition time" of thirty minutes is recommended.

6. Set the recorder of data to the fastest rate of acquisition that is possible. Present capabilities for rates of acquisition are 120 samples per minute.

7. Start the recorder. Allow the vessel to idle in gear until a constant vessel speed is achieved.

8. Verify that the throttles are synchronized and that the trim tabs are fully raised.

9. Perform a rapid acceleration. Leave the engines at full throttle until the vessel has reached full speed. After the vessel has reached full speed, leave the engines at full throttle for an additional 5 seconds.

10. Bring the throttles back to low idle. Allow time for the vessel to slow down. Allow the vessel to reach a constant speed.

11. While the transient recorder is still recording, repeat Step 7 through Step 10.

12. The "Sea Trial Transient" test has been completed.

Next, the steady state data must be recorded. The setup of Cat ET requires a group of default channels to be selected prior to performing the "Sea Trial Steady State test". An example for a 3126B engine with 335 kW (450 hp) can be found in the "3126B Marine Performance.set" file. The file already exists in version 2001A of Cat ET. The file also exists in newer versions of Cat ET. The file has predefined ECM and manual data channels. The file can be selected and a new name for the file can be assigned. The data can then be recorded. The default group of channels can be modified, if necessary. The manual channels that must be recorded are the measured fuel rate and the exhaust temperature before the turbocharger. These manual channels must be entered into the keyboard after being prompted by Cat ET.

The frequency of data points that must be acquired is dependent upon the rated engine speed. For engines that have a rated speed of 1801 RPM or higher, obtain data points at low idle and at 1000 RPM. Next, obtain data points at every 200 RPM increment up to 300 RPM of the rated speed. Finally, obtain data points in 100 RPM increments up to full throttle.

Note: In order to achieve the best results, try to acquire all of the data while the vessel is traveling in one direction. Currents and wind are definite factors in the performance of the boat and in the loading of the engine.

Once the sea trial has been completed, the data should be analyzed. Transfer all three data files to the "Sea Trial Database". The following data files should be uploaded to the database:

• "General Information" (file extension ".txt")

• "Steady State" (file extension ".ssd")

• "Transient" (file extension ".ssd")

This data is stored for future reference. The data can be compared to more recent data in order to help diagnose a complaint. In order to access the database, go to "http://engines.cat.com/infocast/frames/marine/products/general/seatrial/".