[s-cars] Hose leak and boost gauge 'tap' location

[Kirby Smith]

Normally, engine vacuum is measured on the engine side of the throttle
as you are.  At this location a leak in the pre-throttle plumbing won't
be noticed as less vacuum.  All you will get is wrong mixture.

kirby

"Mock, Bruce J (Bruce)" wrote:
>
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> Hey all
>
> need to tap into the collective knowledge database...
>
> hopefully this is an easy one..
>
> I've been noticing lackluster acceleration coupled with a loud Whooooshing sound under heavy boost coming from the right front area of the engine bay on my '93 S4 lately...  Upon further investigation - sure enough - I found a hole about the size of my little finger in the turbo to crossover pipe hose.
>
> Even with this gaping hole, my boost gauge behaves absolutely normally: - it reads ~13 in. vacuum at idle and reads ~ 19 -20psi boost under max accel.  (This is with an MTM 270 chip)  So what gives here?  The main reason I installed a boost gauge was so that I would know if (when) I ever had a leak in the system.
>
> My boost gauge is 'T-ed' in on the line that runs down to the ECU - right near the moisture trap along the firewall  - this is the line that is notorious for popping off all the time on our cars.
>
> Here is the question:  Am I measuring the vac/boost in the wrong place?  It would seem that this is so.  After all, why is the gauge telling me there is ~19psi boost when this is obviously NOT the case?  DUH - Must be BC I am not measuring the boost in the correct place.
>
> Where are you guys tapping in to measure vac/boost?  It seems that we would want to measure vac/boost that is present IN the intake Manifold.
>
> Am I missing something here?
>
> Thanks
>
> Bruce
>
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