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We do fuel injector ultrasonic cleaning, flow testing, and service for all makes and models of Jaguar fuel injectors,  Porsche, BMW, Mustangs, Buick Grand National, Camaro,  Firebird, and other MPI injectors.


This page deals with information regarding the Jaguar vacuum thermal valve.  EAC5086   EAC 5086


There is very little information available in any Jaguar service manual (or elsewhere) on the operation of this valve.   As a result, I developed this page, to give you some first hand information on how this valve operates, and the correct plumbing of the vacuum hoses for this valve.


This particular vacuum valve is threaded into a boss on some (but not all) of the Jaguar fuel rails.  Located on  a boss on the B bank side of the fuel rail,  between injectors 2B and 3B.  


The specific purpose of this thermal valve is to eliminate fuel vapor lock, resulting in a  non starting of the engine, which may occur at elevated engine temperatures.


A sketch of this valve is shown below for reference.....




Port A connects via a vacuum hose to the vacuum port on the B bank FPR (fuel pressure regulator).  Port B connects via a vacuum hose to a stub on the front of the B bank intake manifold.  


Thermal valve operation....


This valve is "activated" when fuel rail temperatures meet or exceed 70 degrees C (156 degrees F).  


Below a fuel rail temperature of 70 degrees C (156 degrees F),  the air port within the valve is open.  With the air port open, the B bank fuel pressure regulator receives B bank (engine) vacuum.  This is normal engine operation.


If fuel rail temperature meets or exceeds 70 degrees C (156 degrees F), then the thermal vacuum switch is activated.  Activation of the thermal vacuum switch, closes the air port within the thermal valve, shutting off vacuum to the FPR (fuel pressure regulator).   An additional +/- 2 psi is imposed on the FPR, which creates aditional fuel pressure and additional fuel flow thru the FPR, and into the fuel rail.  The added fuel pressure forces fuel vapor out of the fuel rail, and the fuel pump now supplies liquid fuel to the rail.


When fuel rail temperature falls below the 70 degree C (156 degree F), the port within the vacuum switch opens,  and intake manifold vacuum is restored to the FPR,  and fuel vapor has been purged from the fuel rail.


There is also a square cap that fits over the plastic body portion of thermal switch.  Removable with a very thin blade screwdriver.  Gently pry the cover (cap) up from the bottom side of the cap, with your thin blade, releasing the locking tabs located on both sides of the cap.  Inside is a small square cavity, wherein was once a tiny piece of foam rubber. ..most likely long ago deteriorated.  Remove the old foam, and leave the square cavity vacant...if you don't perform annual service.  If you are one who keeps a maintenance list, install a piece of cotton, and check/replace the cotton annually.  Be sure the vacuum ports, as well as the vacuum hose, are not clogged with deteriorated foam bits.  Blow the ports out with compressed air, or perhaps a paper clip.


Testing the vacuum thermal valve....


The thermal valve can be easily tested for proper operation.  It only takes about 30 minutes, and a minimum of tools.

1)  To will need the following items...
      a) a pair of pliers
      b) two short sections of vacuum hose, about 1 foot long each...3/16" ID.
      c)  a thermometer
      d)  a pan of water
2)  Remove both vacuum hoses from the valve.  Be careful not to break off the plastic hose nipples.  Use a razor knife if necessary to cut the hoses.
3)  Unscrew the valve from the rail
4)  Fill a small pan about 1/2 full with water, and place on a stove burner
5)  Place the thermometer in the pan
6)  Fix one test section of vacuum hose onto each port on the valve
7)  Blow thru one hose (it doesn't matter which one).  You should be able to hear/feel air escaping from the open end of the other hose.
8)  Using the pliers,  grasp the valve, and lower the threaded end of the switch in the water.  Do not immerse the plastic.
9)  Turn on the stove burner, and slowly raise the water temperature in the pan
10)   Below a water temp of 156 degrees F, you should still be able to blow air thru the hoses
11)  When the water temp reaches appx 156 degrees F, you should hear a slight click from the valve, as the air port in the valve closes, and you should now NOT be able to blow air thru the hoses.
12)  If the valve doe not operate as per above..the valve is bad and needs replacing.

If the valve is can leave the valve off the rail, and route a section of vacuum hose from the fuel pressure regulator to the stub on the intake manifold.  But you need to doing will not have the vapor purging effect that the valve provides.

If the valve tests good, reinstall with new vacuum hoses (routed as previously described).  There is no need to use any sealant.  Maybe a bit of anti-seize on the threads of the valve...after you clean up the threads on the valve, and the threads on the boss on the rail.      


Other electric switches have subsequently replaced the vacuum switch, on later models.  However, the end result is the same.


This particular thermal vacuum  switch (EAC5086) is very difficult to locate, and expensive to purchase.  Vendors often ship the incorrect part, creating added down time for your vehicle, and added frustration.


I have a very limited availability of these vacuum switches.  Removed from fuel rails that I have.  They have been cleaned, and tested, and guaranteed to be operational.  Cost is subject to current availability.


NOTE ABOUT  FUEL LEAKING FROM VACUUM VALVE : This is not usually a malfunction of the valve.  As mentioned above, Port A of the valve connects to the B bank fuel pressure regulator.  If the fuel pressure regulator has a split or rupture of the rubber diaphram within the regulator, the fuel within the regulator will seep into the hose connected to the vacuum valve. If you remove that hose, and fuel is present, 99.9% chance you need to replace that fuel pressure regulator.


Above info is provided free for Jaguar owners, by to assist you in maintaining your engine.


If you need one...send me an E-MAIL


To go to my web site home page...please click  HERE


For pricing on injector flow testing, and ultrasonic cleaning, please click HERE


                                                                Jaguar Fuel Injector Service 
                                                                        Owner    SD Faircloth
                                                                      14869 Yellow Water Lane
                                                                      Jacksonville, Florida   32234