My oil pressure gauge is at 400 kpa. what caould cause this?

NO , there is not a fuse just for those two thing's ! There are two power supply's for the whole insturment cluster . You could need a new cluster or the ECM isn't sending this info. to the cluster . Could have DTC'S - diagnostic trouble codes stored in the PCM or the insturment cluster . Without knowing how this works (insturment cluster gets it's info.) Your best bet , take it to a qualified repair shop that has the knowledge and test equipment to diagnose this problem.
Engine Oil Pressure Gage
The instrument panel cluster (IPC) displays the engine oil pressure as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the engine oil pressure. The engine oil pressure gage defaults to 0 psi (0 kPa) or below if:
• The ECM detects a malfunction in the engine oil pressure sensor circuit.
• The IPC detects a loss of serial data communications with the ECM.
For the 4.2L LL8, the ECM uses an engine oil switch that is open when the oil pressure is normal and closed when the oil pressure is low. At normal pressure, the engine oil pressure gage will display 275 kPa (40 psi). At low pressure, the gage will go to 0 kPa and the low pressure warning will be displayed in the driver information center (DIC). At high pressure, the gage will display 551 kPa (80 psi). Any values between these three values are calculated values determined by the ECM.

Voltmeter
The instrument panel cluster (IPC) displays the vehicle voltage based on the information from the body control module (BCM). The IPC uses the serial data information from the BCM to provide a voltage level indication on the voltmeter.

DTC P0521: Engine Oil Pressure (EOP) Sensor Performance

DTC P0522 Engine Oil Pressure (EOP) Sensor Circuit Low Voltage
DTC P0523 Engine Oil Pressure (EOP) Sensor Circuit High Voltage

Volt Gage Inaccurate or Inoperative
2
Install a scan tool.
Turn the ignition ON, with the engine OFF.
With the scan tool, perform the instrument panel cluster (IPC) gauges output control.
Does the volt gauge move up and down when commanded?

There is no fuse for the oil sending unit ! Oil lite on , gauge not working ? Do you know what PCM five volt reference voltage is ? The PCM - engine computer supply's a stable 5 volt voltage to engine sensors . The oil pressure sensor is one of these sensors .
Engine Oil Pressure Sensor
The engine oil pressure sensor is a solid state transducer. The engine oil pressure sensor sends oil pressure information to the PCM. The PCM then transmits the oil pressure information to the IPC via serial data.
Engine oil pressure is displayed on the scan tool in volts. A low voltage reading indicates low oil pressure. As the oil pressure increases, the voltage level also increases. The normal range of the engine oil level sensor signal voltage is 0.5 volts at 0 kPa (0 psi) to 4.5 volts at 883 kPa (128 psi).

Knowing how these gauges work , I'd say you have an instrument cluster problem not oil sender unit. 2003 - 2006 GM had bad stepper motors in the instrument cluster . If there was a problem with the oil sender the gauge would default to zero .
Engine Oil Pressure Gage
The instrument panel cluster (IPC) displays the engine oil pressure as determined by the powertrain control module (PCM). The IPC receives a class 2 message from the PCM indicating the engine oil pressure. The engine oil pressure gage defaults to 0 kPa (0 psi) or below if:
?€¢
The PCM detects a malfunction in the engine oil pressure sensor circuit.

?€¢
The IPC detects a loss of class 2 communications with the PCM.

If you don't know what class 2 serial data communications are ,google it. How to repair GM Instrument Cluster Speedometer Gauge Stepper

The computing system on your vehicle has no safe mode for running low on oil . The only thing that will happen is the check gauges light will come on.
The oil pressure gauge is an analog device that is located in the IPC. The oil pressure gauge is operated directly by the oil pressure sensor circuit. As the engine oil pressure changes, the resistance of the sensor and the current flow in the oil pressure gauge changes. The current flow in the oil pressure gauge causes the needle to move in order to appropriately display the engine oil pressure. A sensor resistance of 1ohms will display as 0 kPa (0 PSI) and a resistance of 88 ohms will display as 80 kPa (80 PSI ). The IPC also monitors the oil pressure sensor circuit and interprets the current flow in this circuit in order to determine when the engine oil pressure is too low. If the oil pressure is too low, the check gauges tell tale will turn on. The oil pressure sender is located on the left side of the 2.2L. The 4.3L engine, oil pressure sender is located at the top left side, near the distributor/high voltage switch.
Try disconnecting the battery cables an hold them together for ten minutes , reset ECM !

You have a oil pressure switch which is located by the oil filter,it is screwed into block,just removed electrical connector,get wrench and remove.

• When the oil pressure is either high or low it will either turn the oil light "on" in the dash or move the gauge to the extremes
• Undetected high or low oil pressure can result in internal engine damage and/or gasket leakage. Here's a picture of what it look's like.

http://www.autozone.com/external-engine/oil-pressure-switch/duralast-oil-pressure-switch/chevrolet/s10-p-u-2wd/2002/6-cylinders-w-4-3l-sfi/31135_652060_8450

You should have a test port on the Fuel Supply rail, use a tool from a local auto parts "Tool Loaner program" where you can borrow tools for free,w/a deposit of course,then follow the steps provided;

MPI Fuel System Pressure Test

The MPI fuel system used in vehicles equipped with a 4.OL engine employs a vacuum balanced pressure regulator. Fuel pressure should be approximately 55-69 kPa (8-10 psi) lower with the vacuum line attached to the regulator than with the vacuum line disconnected. System fuel should be 214 kPa (31 psi) with the vacuum line connected to the regulator and 269 kPa (39 psi) with the vacuum line disconnected. CAUTION: Some fuel may be discharged when connecting fuel gauge to fuel rail.

1. Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to test port pressure fitting on fuel rail (Fig. 7).
2. Remove vacuum line from pressure regulator.
3. Start the vehicle.
4. Note gauge reading. With vacuum line disconnected, fuel pressure should be approximately 269 kPa (39 psi).
5. Connect vacuum line to pressure regulator. Note gauge reading. Fuel pressure should be approximately 214 kPa (31 psi).
6. If fuel pressure is not approximately 55-69 kPa (8-10 psi) higher with vacuum line removed from regulator, inspect pressure regulator vacuum line for leaks, kinks or blockage. CAUTION: Fuel pressure will rise to as much as 655 kPa (95 psi) when the fuel return tine is pinched shut, shut engine down immediately after pinching oft fuel return line.
7. If fuel pressure is low, momentarily pinch shut the hose section of the fuel return line. If fuel pressure remains low, inspect the fuel supply line, fuel filter, and fuel rail inlet for blockage. If fuel pressure rises replace fuel pressure regulator.
8. If fuel pressure is above specifications, inspect the fuel return line for kinks and blockage.

Capacity Test

1. Remove the cap from the pressure test port in the fuel rail.
2. Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to the pressure fitting on the fuel rail (Fig. 7).
3. Start the vehicle. Pressure should be approxi- mately 214 kPa (31 psi) with the vacuum hose connected to the pressure regulator and 269 kPa (39 psi) with the vacuum hose removed from the pressure regulator.
4. If the pressure is not to specification, check the following before replacing the fuel pressure regulator:

• 4a - Inspect the fuel supply and return lines/hoses for kinks or restricting bends
• 4b - Check the fuel pump flow rate. A good fuel pump will deliver at least 1 liter of fuel per minute with the fuel return line pinched off. If the fuel pump does not pump adequately, then inspect the fuel system for a plugged fuel filter or fuel pump inlet filter (sock). Fuel pump flow rate can be done by connecting one end of an old A/C gauge hose to the fuel test port on the fuel rail and inserting the other end of the hose into a container of at least 1 liter capacity. Run the fuel pump by installing a jumper wire into diagnostic connector terminals D1-5 and D1-6. Be sure to pinch off the fuel return line or most of the fuel will be returned to the fuel tank.

The ford spec listed in the ford engine control manual is:

General Specifications Item Specification Fuel tank capacity 71.9L (19 gal) Fuel Pressure Hot restart 448-482 kPa (65-70 psi) Key ON Engine OFF (KOEO) 140-415 kPa (20-60 psi) Key ON Engine Running (KOER) 170-280 kPa (25-40 psi)

Are you measuring the fuel pressure with a mechanical gauge or are you using a scan tool . If with a mechanical gauge, does the gauge have an air purge? What symptoms does the vehicle present. If running rough you could have a fuel injector leaking. Are you measuring the fuel pressure with the key on engine off? If so, did you cycle the key a few times? Good luck

go to auto zone to get a free obd check... just tell the worker your check light is on caould you help me. or simply just look at your gauges and make sure everything is ok. full fuel tank, coolant and oil pressure too

gauge or sender may be faulty

hi! there,well actually oil pressure that you get in your gauge seems to be that you need to change oil it was below to the standard oil pressure of engine,approximately 275 kpa is 39 psig
w/c is below to 90 psig,the important here is you to avoid/prevent knocking your engine and besides this very significant of sensoring
engine activities to prevent mor costly maintenace in your car.so sent your car to service car center to change oil specially also to change your oil filter.thank/s