ok guys im not sure if this is normal but from working on cars for many years , i dont think it is


ok so our evo came with a dealer installed boost gauge. the line is t'd from the intake manifold to the regulator on the rail.


heres the problem from time to time my gauge stops reading vacum at idle happens maybe once or twice a day. today i got pissed of and just to double check i unplugged the hose from the regulator, needless to say it had no vacum plugged it back in and within 2 seconds the gauge started reading vacum again so i went back under the hood unplugged the regulator vacum hose and it had vacum. is this normal? i have already preassurized the system and it shows no leaks what so ever.

 

You might have a slightly kinked boost line for the gauge.
When the motor rocks back and forth, it could be pinching the line.
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i think hes trying to say he isnt gettin vacum from the source line correct?

 

thats correct, the source is loosing vacum

 

When you loose vacuum what is the idle doing? When is the car doing this? Can you see a trend (temp changes, lift throttle @ high RPM, etc.)

 

the car feels the same no changes, no temp changes

 

Mine does this too. But I have an autometer gauge T'd off the fpr line. Sometimes at idle occasionally it wont read any vacuum but when I boost it will still show positive PSI. Eventually it shows vacuum after a while of driving, just gets stuck sometimes i guess

 

same issue

 

sounds like a faulty gauge to me? did you switch out gauges?

 

if it was a faulty gauge when i unplug the regulator vacum line i should feel vacum in the line that connects to the regulator. There is no vacum there at all. then after a minute vacum comes back

 

Looking at the vacuum lines for the FPR. It passes through a vacuum switching solenoid (VSS) then goes directly into the manifold.

If your t-eed at the FPR, then it makes sense to loose vacuum if the solenoid is closed. Then comes back because the solenoid opens back up.
I suggest teeing directly to a manifold source.
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