After diagnosis computer indicates faulty fuel pump. Sympton: Engine light comes on intermitently (light with wrench symbal) and the fuel gauge goes crazy at same timegoing from full to empty and back

Remove the gauge cluster and check for a bad ground. If it is bad you can resolder the trace on the back of the cluster back to the groung pin for the connector.

There is no module under the dash on your vehicle .
P0463 - Fuel Level Sensor A Circuit High Description: The powertrain control module (PCM) monitors the fuel level input (FLI) circuit for electrical failure. The test fails when the signal moves above the maximum allowable calibrated parameter for a specified fuel fill percentage in the fuel tank. Possible Causes:

• Fuel pump (FP) module concern
• Incorrectly installed fuel gauge
• Damaged instrument cluster
• FLI shorted to VPWR
• CASE GND circuit open
• Overfilled fuel tank
• Damaged fuel gauge

Diagnostic Aids: See the diagnostic aids for DTC P0460. Application Key On Engine Off Key On Engine Running Continuous Memory Ranger GO to Pinpoint Test HX . All others Refer to the Workshop Manual Section 413-01, Instrument Cluster for fuel level indicator diagnosis.
You start by taking to Dealer or someother qualified repair shop .
Instrument Cluster Diagnostic Trouble Code (DTC) Index DTC Description Source Action B1202 Fuel Sender Circuit Open Instrument Cluster Go To Pinpoint Test B . B1204 Fuel Sender Circuit Short to Ground Instrument Cluster Go To Pinpoint Test B .

Hook up a fuel pressure gauge to the schraeder valve, and then operate the vehicle. I'll bet you will see a corolation between the performance and the fuel pressure. This would indicate a failing fuel pump.

First thing you need to do is have the actual pressure verified by attaching a mechanical oil pressure gauge in place of the sending unit on your engine. If the gauge verifies your dash readings then you have an oil pressure loss inside the engine that needs further diagnosis (worn bearings, obstructed pump pickup etc). If pressure drops enough to turn the light on I would not drive it 'till you know exactly what's happening inside or you can and will have an engine failure.
One warning...if after you remove the pan, you find that the pump screen is not obstructed, Don't blame the pump for the low pressure.....check the bearings. However, regardless of what you find (obstruction or worn bearings) it is advisable to replace the pump. Pumps generally don't fail but ingesting debris (carbon or metal from bearings) will either score or wear the pump housing and vanes enough so that the pump will never reach full pressure.
If the external gauge shows normal pressure, contrary to what the dash gauge tells you, blow out the sender passageway and replace the sender, then add marvel oil at each oil change as it will help dissolve any crud accumulated inside the oil system.

1 Listen for unusual sounds when you try to start the car. No sounds indicates a problem with the ignition. If you hear a clicking sound, the starter is faulty. If the car starts for a moment then shuts off, you may hear a knocking noise. This can be from a faulty fuel injector or the individual components of the system, such as the fuel filter, fuel pump or hoses.
2 Check the fluid levels in your BMW. Little or no fluid can cause your engine to seize up and not be able to start. It can also cause more severe engine damage if it goes on for too long. Checking your fluids can also alert you to any leaks within the engine. Some drivers have reported leaks in the cooling system that can cause overheating problems. There have also been reports of power steering hoses failing and leaking. By checking your coolant and power steering fluid, you can diagnose if they are the problem.
4 Add gas to your tank. Although the BMW 540i has a gas gauge that indicates the fuel level, in some cases the gauge may be faulty. After adding fuel, attempt to start the car again.
5 Note any smells that may be coming from the engine. When your engine was still running, you may have noticed odors, such as a burning or oil smell. This would indicate that the engine is leaking, and fluid is burning off in the engine. Some owners on Repair Pal have reported complaints with the 540i that the valve cover, intake manifold and PCV plate leak oil after 60,000 miles.

You have an engine control unit, but that is rarely the problem. Is your engine light on? If yes, let me know and I'll send procedures for extracting the trouble codes that may identify the problem.
If no engine light, the first thing I would check is the fuel pressure regulator. Pull the vacuum hose off the regulator and plug it with a golf tee. Start the engine and see if gas comes out the vacuum port on the regulator. Is indicates a busted diaphram. Even if the diaphram is good, I would then borrow a fuel pressure gage and run the tests below to make sure the regulator is working to keep the pressure at 39psi. Let me know if this isn't it or you have more questions.

1. Relieve fuel system pressure.
2. Turn ignition switch OFF and disconnect the negative battery cable.

When disconnecting any fuel system hoses, always place a shop towel to prevent residual fuel from spaying.

1. Disconnect the high pressure hose at the delivery side. Using a fuel pressure gauge and adapter (09353-24000 or equivalent), install the adapter to the delivery pipe.
2. Connect the negative battery cable.
3. Activate the fuel pump, by applying battery voltage to the fuel pump drive terminal. Check that there is no leakage from pressure gauge or connections.
   

Fig. Fig. 12: Fuel pump drive terminal location-Excel

1. Disconnect the vacuum hose from the pressure regulator and plug.

Fig. Fig. 13: Fuel pump drive terminal location-Sonata

1. Operate the engine at idle and check the fuel pressure. Fuel pressure should be 47-50 psi (330-350 kPa).
2. Reconnect the vacuum hose to the pressure regulator. With the engine idling, fuel pressure should be 39 psi (270 kPa).
3. If the specified values are not met, make the necessary repairs, as indicated in the diagnosis chart.
4. Shut the engine OFF. Check that the fuel pressure is maintained at the value indicated in Step 8, for approximately 5 minutes.
5. Relieve the fuel pressure.
6. Remove the fuel pressure gauge and reconnect the high pressure hose, using a new O-ring.
7. Start the engine and check for leaks.

Replace the oil pressure switch on the engine. They do go bad. also the switch is used to run current to the fuel pump upon starting everytime. When the oil pressure reaches normal pressure the computer shuts it off and the sends a signal to the fuel pump relay to take over running the fuel pump
This oil switch has three wires attached to it

What sensors did you replace? It sounds like a problem that could be caused by something in the evaporative emission system, like a faulty purge solenoid or evap cannister problem. Does the tank take fuel slowly when filling up? You could also have a faulty gas cap. That is the first thing I would look at. It is an integral part of the evap system. Hope this helps and best wishes.

Try mass air flow sensor, or idle control system/ sensor. Could also be faulty coils or loose or damaged wires in the ignition circuit. Cheapest way to find out is an auto wrecker. You can probably get all those and more for a hundred bucks. Don't be afraid of used parts. You drive on them every day.

1st check the #4 fuse (10A) and #10 fuse (7.5A) on the 'under-dash' fuse block.
then #9 fuse (10A) on the 'engine bay' fuse block.

if the fuses are good, the gauge assembly has has "self-diagnostic" feature.

Self-diagnostic Procedure

The gauge assembly has a self-diagnosis function.
. The beeper drive circuit check
. The indicator drive circuit check
. The LCD segments check
. The gauges drive circuit check (speedometer, tachometer, fuel gauge, coolant temperature gauge)
. The communication line check (the coolant temperature signal line between the gauge and ECM/PCM)


Entering the Self-diagnosis Function:
1. Push and hold the trip/reset button.
2. Turn the lighting switch ON.
3. Turn the ignition switch ON (ll).
4. Within 5 sec., turn the lighting switch OFF, then ON and OFF again.
5. Within 5 sec., release the trip/reset button, then push and release the button four times repeatedly.

NOTE:
. While in the self-diagnosis mode, the dash lights brightness controller operates normally.
. While in the self-diagnosis mode, the trip/reset button is used to start the beeper drive circuit test and the gauge drive circuit check.
. lf the vehicle speed exceeds 1.2 mph (2 km/h) or the ignition switch is turned OFF, the self-diagnosis mode ends.

The Beeper Drive Circuit Check:
When entering the self-diagnosis mode, the beeper sounds five times.

The Indicator Drive Circuit Check:
When entering the self-diagnosis mode. the indicators lights (such as: Seat belt indicator light, Door/hatch indicator light, Brake system light. Charging system light, Low fuel indicator light, maintenance required light) blink.

The LCD Segment Check:
When entering the self-diagnosis mode, the odo/trip segment blinks five times.

The Gauge Drive Circuit Check:
When entering the self-diagnosis mode, the speedometer, the tachometer, the fuel gauge, and the coolant
temperature gauge needles go from the minimum position to maximum position, then return to the minimum position.
NOTE:
After the beeper stops sounding and the gauge needles return to the minimum position, pushing the trip/reset button, starts the beeper drive circuit check {one beep), and the gauge drive circuit check again.
The check cannot be started until the gauge needles return to the minimum position.

The Communication Line Gheck:
In the seif-diagnosis mode, after the odo/trip LCD segments check, the self-diagnosis starts the communication line check.
lf all segments comes on, the communication line is OK.
lf the word" Error" is indicated, there is a malfunction in the communication line between the gauge assembly, the multiplex control unit, and the ECM/PCM,

Ending the Self-diagnosis Function:
Turn the ignition switch OFF.

Note: lf the vehicle speed exceeds 1 .2 mph (2 km/h), the self-diagnosis function ends.
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If everything works correctly during the check, check your VSS (vehicle speed sensor)