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4.6 V8 GEMS vacuum circuit

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Good morning folks,

as shown in pics, i found 4 vacuum takeoffs, 2 in trumpet base and 2 in plenum.

Take off nr. 1, left hand side of the plenum: unknown, maybe is part of idle circuit?
Take off nr. 2, left hand side of the plenum: connection of the PCV system, left hand bank
Take off nr. 3, left hand side of the trumpet base: connection to fuel pressure regulator
Take off nr. 4, right hand side of the trumpet base: probably is the other connection to the PCV system, right hand bank where oil separator is fitted.

I can't find the connection for vacuum brake booster...



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There is no brake booster take off on these, all the P3 V8 Range Rovers had 'hydroboost' brakes, as opposed to vacuum assist.

Looks to me, that #4 would likely do the job for you nicely, you can unscrew them and move them to other ports drilled in the plenum base, if it makes things easier.

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Suspect #1 is the charcoal canister for the fuel tank vapours, #2 is crank vent.

#3 is for fuel pressure regulator, #4 would be brake servo on cars that had it, although they had a valve there to prevent a backfire from popping the servo diaphragm so its worth checking.


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Many thanks.

Yes, nr. 1 is part of EVAP system for gasoline vapours, i dounbt i can use it as vacuum source because it's connected BEFORE throttle, so i can just plug it.


Nr. 2 and 4 are both for crank vent, as P38 has a closed venting system: nr. 2 works at full throttle conditions and nr. 4 at idle/cruising condition.


So for my brake booster vacuum i can drill a new opening in trumpet base or just put a T on nr. 4 opening and use this vacuum point both for brake booster and crank venting.

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