Info required from anyone with an intercooler, HPFP, and boost gauge fitted

[xxx_mojo_xxx]

What's the vacuum pressure being shown during idle?

Thanks,

Mo

[bacillus]

iirc should be around -20 but don't quote me on it... 

[john_o]

yep around 20mmHg vacuum at idle 

[xxx_mojo_xxx]

Is it a good or bad thing if it's below 20?  Should I be expecting imminent failure?

What intercoolers do you have?

[bacillus]

Is it a good or bad thing if it's below 20?  Should I be expecting imminent failure?

If it deviates much from -20 then I would look for a vacuum leak.

[GTIjames]

I'm running the defi boost gauge with apr hpfp and forge fmic

When I first turn on the engine I have noticed boost sits a little higher than 22hg around 15hg the revs also sit a liitle higher c1100rpm rather than usual 8krpm 

It soon settles down once warmed up and boost will then sit at 22hg

I have suspected a vacuum leak but holds boost well, so just put up with it   

[john_o]

agree not seen a gti yet thats below 20mmHg when warm ...
first place to check are the boost guage connections, which guage and how have you fitted it (t piece etc?)

if the revs are above idle then itll naturally be less of a vaccuum, mines the same during the warm up phase its normal

[xxx_mojo_xxx]

Is it a good or bad thing if it's below 20?  Should I be expecting imminent failure?

If it deviates much from -20 then I would look for a vacuum leak.

Where would I start checking for a vacuum leak?

Am I correct to think the turbo boost pipe and intercooler pipes only carry positive boost?

[bacillus]

I think most find that the issue lies where you tap off the vacuum for the boost gauge so I would check that first.

[xxx_mojo_xxx]

I think most find that the issue lies where you tap off the vacuum for the boost gauge so I would check that first.

Sorry to be really ignorant...but does anyone have a pic?

[john_o]

the way in which a boost/vacuum signal has been taken depends on the make/type and parts you have fitted to your car.


normally there will be a T piece fitted under the engine cover RHS as looking from front and a small bore pipe running into the cabin then into boost gauge.
(or if its a DEFI electrical gauge then the small bore pipe runs to a sensor usually in the engine bay then an electrical cable to the cabin/gauge)

if you have a forge DV fitted then theres also a 'takeoff' point there which can be used negating the need for a t piece.

Id look for

1. broken plastic  t piece with a hariline crack , put a metal one in there ...
2. check all fittings that have been touched during install, inc the one on the back of the boost guage

another thing you can try is spraying some fairy liquid water around connections and listening/checking gauge.
you may get a momentary inc in vacuum  or change in sounds if it temporarily stops the leak.
or with some throttle get bubbles .....

[NEWEY]

once warm mine sits at 22hg

[ukdub]

once warm mine sits at 22hg

Same as mine when warm.  Read using a Defi boost gauge. 

[NEWEY]

once warm mine sits at 22hg

Same as mine when warm.  Read using a Defi boost gauge. 

sorry forgot to add mine is a newsouth boost gauge :)

[xxx_mojo_xxx]

Thanks for the tips guys especially around isolating a potential vacuum leak.

I was using a Forge DV and running the 'vacuum' pipe directly from it.  I figure if everyone has a reading of 22 then there might not be a problem after all!!!

I guess the intercooler and HPFP must have increased the vacuum pressure.  As a test I removed my Forge DV and went back to the OEM one (rev. D)  and the read outs are the same.

I must say I'm missing the "whoosh" noise from the Forge DV.... not sure if I should fit that one back again.  Open to opinions?