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We provide fuel injector flow testing and ultrasonic cleaning of fuel injectors for all makes and models of the Jaguar engine.  In addition to Jaguars, we can also provide injector flow testing and ultrasonic cleaning for almost every vehicle out there.  We can service top-feed injectors only.  No side feed, and no service for direct gas or direct diesel injection.


We have provided this web page as a courtesy to Jaguar V12 owners in an attempt to explain operation of the fuel pressure regulators (FPRs) on the 5.3 liter HE V12 engine, as well as the 6.0 liter engine.  In the near future, we hope to add operation of the FPRs on the earlier pre-HE engine.


All 5.3 liter V12 HE Jaguar engines from stock contain two fuel pressure regulators.  To get you oriented correctly,  while you sit in the driver seat, whether the steering wheel is on the left (US spec), or on the right (Euro spec) , the engine banks are referred to as follows.  A bank is on your right.   B bank is on your left.


Now with the above said...let us discuss the A bank FPR.   This is Bosch part number 0280160234.  It is rated at 3 Bar pressure...(43.5 psi).  The FPR is stamped on the side body with these numbers.  While it is called everywhere as a FPR, its' function is more of a pressure damper...used to keep a constant fuel pressure between the fuel pump and the fuel rail.  The straight line distance between the fuel tank and the A bank FPR is more or less 10 feet.  Add maybe 2 feet for the twisting, curving fuel pipe perhaps 12 feet.   The fuel pump delivers appx 90-100 psi of dead head pressure to the FPR.  Under the various engine operational scenarios, that fuel delivery pressure to the fuel rail has a tendancy to fluctuate.  The A bank FPR eliminates those pressure fluctuaions.  There have been some reports that removing the A bank FPR has not caused any difference in engine performance.  It's up to you to evaluate on your engine, whether this is so.


On now to the B bank FPR.   THIS is the item that actually controls fuel pressure delivered thru the fuel injectors to the engine.  Fuel pressure ( via this FPR) keeps a constant pressure between the injector pintle and the intake manifold vacuum  (which varies under different  engine operational conditions)  at a constant 2.5 Bar...(36.25 psi).  The ECU is programmed (mapped) to vary injector pulse width ( open/close time) expecting that the differential pressure is 2.5 Bar.


With age, either A bank, or B bank FPR may fail.  The typical fault is the FPR rubber diaphram cracks, and will cause eratic fuel pressures.  More so, a cracked FPR diaphram will cause fuel to leak thru the damaged daiphram and into the engine intake manifold...causing a hard or no start engine.


The simple test to determine if you have a cracked/ruptured FPR diaphram is to remove the rubber vacuum hose from the FPR and check for leaking fuel from the hose or the FPR.  If you see such, the FPR needs replacing.  And while there, you should replace the rubber vauum hose.


We do not sell FPRs.  We do injector flow testing/cleaning.  Google the above FPR numbers if you have a faulty FPR.  You will find numerous sources.


If you are a DYI Jag owner, or a shop that landed on our site, and you found the above info corrected your engine problems, and saved you $$$...we would appreciate your donation for the cause.  See this link if you feel so inclined...  TIPPING 


Thank you,


SD Faircloth
Jacksonville, Fl