FUEL-07, Fuel Pressure Regulator - General Information and Replacement


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General Information

For years, 944 owners and even experienced Porsche mechanics, have on a regular basis replaced perfectly good DMEs, fuel pumps, and various other components because of faulty fuel pressure regulators (FPR). However, it's quite understandable as faulty FPRs can display a wide range of symptoms depending on how the regulator fails. Also, the function and location of the FPR is quite often confused with the fuel damper. The fuel damper is on the supply to the fuel rail and functions to "dampen" the pulsations caused by the fuel injectors. The fuel pressure regulator is located on the return to the fuel tank and functions to control the pressure on the fuel rail. The photos below shown typical 944 fuel rail arrangements and the location of the fuel pressure regulator.


Early 944 (Pre-1985.5)


Late 944


944 Turbo


16V 944S / 944 S2 / 968 (Plastic Cover Removed From Rail)

Fuel Pressure Regulator Failure Symptoms:

Tools

Parts

Fuel Pressure Regulator Part Numbers
Part No.
Model
Year
Engine Code
944 110 198 01
944
1982 - 1985
M44.02
M44.04
944 110 198 03
944
1985.5 - 1988
M44.5-10
944 110 198 04
944S / 944 (2.7L)
1987-1989
M44.40
M44.11 Thru 46K 02979
M44.12 Thru 46K 61255
944 110 198 06
944 (2.7L) / 944 S2 / 968
1989 - 1995
M44.11 46K 02980 Forward
M44.12 46K 61256 Forward
M44.41
M44.43/44
944 110 198 03
944 110 198 05
944 Turbo
1986 - 1989
M44.51 / M44.52 Thru 47K 02563
944 110 198 05
944 Turbo
1989 - 1991
M44.52 47K 02564 Forward

Other Procedures Needed

Testing

Without question, one of the best checks for a faulty FPR is to check the fuel pressure at the rail. If you have access to a 0-100 psi fuel pressure gauge , check the fuel pressure at the rail using FUEL-01. Normally a faulty fuel pressure regulator will result in a very high fuel pressure. So, if your fuel pressure is well above the specs provided in FUEL-01, you probably have a bad FPR.

One of the most common failure modes for the FPR is to fail closed to the point that fuel rail pressure is extremely high. The high differential pressure across the injectors causes them to draw excessive current. The excessive current is seen by the injector drivers which subsequently shutdown. If you have a condition where the car will not start or starts and almost immediately dies, try disconnecting the wire for one (1) injector. Attempt to start the engine. If it starts and continues to run, the fuel pressure regulator is likely bad. Bear in mind that running on only three cylinders, the car will run very rough. By disconnecting one injector, it reduces the current enough to keep the injector drivers from shutting down.

Replacement

  1. Disconnect the fuel pressure regulator vacuum line.
  2. Place a catch rag under the regulator fuel line connection.
  3. Disconnect the fuel line from the fuel pressure regulator. Normally this will be a hose clamp that can be removed by either a flat tip or Phillips head screwdriver.

    CAUTION

    Use caution when removing the fuel pressure regulator from the fuel rail as the rail may be under pressure and can spray into your face and eyes. It's a good idea to wear safety glasses while removing the regulator as well as covering the regulator with a rag.

  4. Remove the fuel pressure regulator retaining bolts. (normally 10 mm socket)
  5. Rock the regulator back and forth gently until it is free from the fuel rail.
  6. Install the new regulator in the fuel rail, install and tighten the retaining bolts.
  7. Connect the fuel line to the regulator.
  8. Connect the vacuum line to the regulator.

Clark's Garage 1998