IDLER & BEARING AS 7T4399 - Caterpillar

Control of Pilot Fuel Pressure and Main Fuel PressureRefer to Illustration 5. There is one electrical circuit for both of the fuel control valves. The valves are connected in series. The ECM creates one PWM command in order to control both of the valves. The maximum current flow through the circuit is approximately 2.5 A.Each control valve contains a spring. The spring in the pilot fuel control valve is weaker than the spring in the main fuel control valve. Refer to Illustration 6. The lower spring pressure in the pilot fuel control valve causes the pilot fuel control valve to open when the flow of current is low. A current flow of approximately 1.2 A is required in order to open the pilot fuel control valve. However, the higher spring pressure in the main fuel control valve caused the main fuel control valve to remain closed at 1.2 A. A current flow of approximately 1.3 A is required in order for the main fuel control valve to start to open. A current flow of approximately 2.5 A is required in order to open the main fuel control valve.
Illustration 6 g01384347
Current flow versus total fuel flow for the ARDAn electrical problem with the circuit affects both of the control valves. Therefore, both of the control valves are disabled if there is a short circuit or an open circuit.Test Step 1. Determine the Diagnostic CodeEstablish communication between Cat ET and the engine ECM. Look for the following codes:
3480-16
3480-18
4077-16
4077-17
4077-18Expected Result:One of the above codes is present.Results:
A 3480-16 code and a 4077-16 code are both present. - The fuel enable valve is stuck open. This causes both fuel pressures to be high.Repair: Replace fuel enable valve (18) . Proceed to Test Step 4.
Only a 3480-16 code or a 3480-18 code is present. - The main fuel control valve is not working correctly.Repair: Replace main fuel control valve (20) . Proceed to Test Step 4.
Only a 4077-16 code is present. - The pilot fuel control valve is not working correctly.Repair: Replace pilot fuel control valve (19) . Proceed to Test Step 4.
A 4077-17 code or a 4077-18 code is present. The fuel system pressure is low. - Proceed to Test Step 2.Test Step 2. Check the Pressure at the Outlet of the Fuel Transfer PumpThis test step checks the pressure at the outlet of the fuel transfer pump when the ARD is off.
Insert a tee in line (39) between the outlet of the fuel transfer pump and the forward fuel manifold. Connect a pressure gauge to the tee.
Disable the ARD by setting the value of the "Data Link Disable ARD Status" parameter to "Disabled". The parameter is in "Emissions Parameters".
Start the engine. Observe the fuel pressure on the gauge. Stop the engine.Expected Result:The outlet pressure for the fuel transfer pump is above 450 kPa (65 psi).Results:
The outlet pressure of the fuel transfer pump is above 450 kPa (65 psi). - The outlet pressure of the fuel transfer pump is OK. Proceed to Test Step