BMW Cars 1999-06

Fuel Pressure Regulator

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The fuel pressure regulator is used to keep the fuel pressure in the fuel rail consistent and change the fuel pressure depending on the throttle position. The fuel rail is in a fuel loop between the fuel pump feed and return lines. Because the fuel delivery requirements change depending on the engine's throttle position and engine loads, the fuel injection system must be able to adapt to meet the fuel requirements of the engine's operating conditions during idle, acceleration and steady cruising.

The fuel pressure regulator has a small vacuum line attached to it that allows the pressure regulator to change the fuel pressure in the fuel loop depending upon the intake manifold pressure which changes as the throttle position changes. When the throttle is opened, the manifold vacuum pressure drops off, causing the pressure regulator to increase the fuel pressure in the fuel loop, which increases the amount of fuel delivery at the injectors to provide for the additional fuel needed for the engine to operate properly.

At idle, the manifold vacuum increases and the demands for the rate of fuel delivery are decreased so the pressure regulator decreases the fuel pressure in the fuel loop.



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Fig. The pressure regulator mounts onto the fuel rail-M44 engine shown

Removal & Installation



M42 Engine
Mounted In E30 Chassis
  1. Relieve the residual fuel system pressure.
  2.  
  3. Remove the front intake manifold support brace.
  4.  
  5. Disconnect the vacuum hose from the regulator. Loosen the mounting clamp bolt and remove the clamp.
  6.  
  7. Be ready to catch the fuel that will leak out of the fuel rail. Pull the regulator down and out of the fuel rail.
  8.  

To install:

  1. Inspect the O-ring on the fuel rail inlet of the regulator. Apply a light coating of fresh oil or petroleum jelly to the O-rings. Install the regulator on the fuel rail and mount the clamp. Tighten the bolts.
  2.  
  3. Connect the fuel hose and vacuum hose. Install the front manifold brace.
  4.  

Mounted In E36 Chassis
  1. Relieve the residual fuel system pressure.
  2.  
  3. Remove the front intake manifold support brace.
  4.  
  5. Disconnect the vacuum hose from the regulator. Loosen the mounting bracket bolt and remove the bracket.
  6.  
  7. Be ready to catch the fuel that will leak out of the fuel rail. Pull the regulator out of the fuel rail.
  8.  



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Fig. Remove the front brace to access the fuel pressure regulator-E36 model M42 engine



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Fig. Remove the bolt to remove the fuel pressure regulator-E36 model M42 engine

To install:

  1. Inspect the O-ring on the fuel rail inlet of the regulator. Apply a light coating of fresh oil or petroleum jelly to the O-rings. Install the regulator on the fuel rail and mount the bracket. Tighten the bolt.
  2.  
  3. Connect the fuel hose and vacuum hose. Install the front manifold brace.
  4.  

M44 Engine
  1. Relieve the residual fuel system pressure.
  2.  
  3. Remove the front intake manifold support brace.
  4.  
  5. Disconnect the vacuum hose from the regulator.
  6.  
  7. Remove the large retaining clip and rotate the regulator side to side and carefully pry away using a suitable prytool.
  8.  
  9. Be ready to catch the fuel that will leak out of the fuel rail. Pull the regulator out of the fuel rail.
  10.  



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Fig. The fuel pressure regulator is mounted to the fuel rail-M44 engine shown



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Fig. This fuel pressure regulator is held in place with a large circlip-M44 engine shown

To install:

  1. Replace the O-rings on the fuel rail inlet of the regulator. Apply a light coating of fresh oil or petroleum jelly to the O-rings. Install the regulator into its holder on the fuel rail and install the retaining clip.
  2.  
  3. Connect the fuel hose and vacuum hose. Install the front manifold brace.
  4.  

M50, S50, M52 And S52 Engines
  1. Relieve the residual fuel system pressure.
  2.  
  3. Remove the ECM/DME control module housing cover screws on the right side of the firewall.
  4.  
  5. Remove the rubber strips along the wire duct by carefully pulling them up, then remove the screws from the wire duct and pull it out to allow enough movement in the injector wires to remove the injector electrical plug plate.
  6.  
  7. Remove the oil filler cap and the valve cover trim. Cover the oil fill opening with a clean shop towel, then remove the injector area trim cover.
  8.  
  9. Disconnect the fuel feed at the front of the fuel rail. Remove the two screws holding the injector electrical plug plate. Pull up and remove from the injectors.
  10.  
  11. Disconnect the fuel return line. Remove the two bolts holding the fuel rail and remove the fuel rail by pulling it off with the injectors. Remove the clamp holding the pressure regulator and remove it from the fuel rail.
  12.  



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Fig. Remove the clamp to release the fuel pressure regulator-M50 engine



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Fig. Check the condition of the fuel pressure regulator O-rings before installation

To install:

  1. Check the O-rings on the regulator and replace if necessary. Apply a light coating of fresh oil or petroleum jelly to the O-rings. Install on the fuel rail.
  2.  
  3. Install the fuel rail and tighten the bolts to 6.5-8.0 ft. lbs. (9-11 Nm). Connect the fuel lines. Install the electrical plug plate. Connect the vacuum hose to the regulator.
  4.  
  5. Install the fuel rail cover and the valve cover cladding with the oil filler cap. Install the wire duct and the rubber stripping.
  6.  

S14 And M20 Engines
  1. The fuel pressure regulator is mounted on the end of the fuel rail and has a vacuum line and a fuel line attached to it.
  2.  
  3. Relieve the residual fuel system pressure.
  4.  
  5. Disconnect the fuel hose and the vacuum hose.
  6.  
  7. Remove the two bolts holding the regulator to the fuel rail. Pull the regulator off the fuel rail.
  8.  

To install:

  1. Inspect the O-ring on the fuel rail inlet of the regulator. Apply a light coating of fresh oil or petroleum jelly to the O-rings. Install the regulator on the fuel rail and tighten the bolts.
  2.  
  3. Connect the fuel hose and vacuum hose.
  4.  

Testing



  1. Connect a suitable fuel pressure gauge as outlined in the fuel pressure checking procedures in this section, so the engine can be started and allowed to idle. On some models, if the fuel rail does not have a fitting or the fuel inlet line is metal or inaccessible, the gauge must be installed using a T-fitting where the fuel feed line exits the fuel tank on models equipped, except the E30 M3 models with an in-tank fuel pump.
  2.  
  3. Start the engine, allow the engine to idle and check and note the fuel pressure reading.
  4.  
  5. Disconnect the vacuum hose on the fuel pressure regulator. The fuel pressure should increase between 5.8-10.1 psi (0.4-0.7 bar).
  6.  
  7. Reinstall the vacuum line and the pressure should drop. If the pressure does not change when the vacuum line is removed and reinstalled, replace the pressure regulator.
  8.  


NOTE
The operating pressure of the fuel pressure regulator is stamped on the regulator housing.

 
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