FUEL-07, Fuel Pressure Regulator - General Information and Replacement
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.
Fuel Pressure Regulator Failure Symptoms:
|944 110 198 01||M44.02
|944 110 198 03||M44.5-10|
|944 110 198 04||M44.40
M44.11 Thru 46K 02979
M44.12 Thru 46K 61255
|944 110 198 06||M44.11 46K 02980 Forward
M44.12 46K 61256 Forward
|944 110 198 03
944 110 198 05
|M44.51 / M44.52 Thru 47K 02563|
|944 110 198 05||M44.52 47K 02564 Forward|
Other Procedures Needed
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.
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.
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