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Is It Possible To Have Boost/vacuum Leak And Good Vacuum Reading?

denisonnd

By denisonnd,
in Engines & Forced Induction

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denisonnd Apprentice

denisonnd

Posted
Posted

I was searching internet for information on boost leaks . When people talk about how to tell if you have vacuum/boost leak

they always mention rich or lean AFR's, boost leak tests.

I always thought the easiest way to telll that you might have a boost leak from lower then usual vacuum reading on a boost gauge.

Can you have a boost leak and normal (-20 /-0.67) vacuum reading at idle? It doesn't make sense to me

89CAL Grand Master

89CAL

Posted
Posted

Its not that simple. If the timing fluctuates it can create a little bit more vacuum. Going off the boost gauge might work but I dont believe its definetive.

Do you know what it sits at with 100% positively no leaks?

XKLABA Grand Master

XKLABA

Posted
Posted

depends how bad the leak is and how good the idle control is, the idle control valve will close to get the vacuum right for idle ( which is what causes hunting on most cars as it tries to figure out why it has to go outside its operating range to get idle, basicly ) hunting at idle or unusually high idle are the best tells of a vac leak

GTSBoy Grand Master

GTSBoy

Posted
Posted

It all depends on where the boost leak is. If it is after the throttle, then it could/would cause low vacuum. If it is before the throttle then it simply cannot cause low manifold vacuum. It can still leak outwards like a bitch under boost though.

AngryRB Grand Master

AngryRB

Posted
Posted

I had leaks in the manifold and the intercooler piping and the gauge didn't show any different, off boost it will stall easily, on boost it will feel laggy and black smoke .

Ben C34 Grand Master

Ben C34

Posted
Posted

I was searching internet for information on boost leaks . When people talk about how to tell if you have vacuum/boost leak

they always mention rich or lean AFR's, boost leak tests.

I always thought the easiest way to telll that you might have a boost leak from lower then usual vacuum reading on a boost gauge.

Can you have a boost leak and normal (-20 /-0.67) vacuum reading at idle? It doesn't make sense to me

Of course its possible. There is more chance of popping an intercooler pipe or a dodgy joiner or clamp leaking under boost than something leaking in the inlet manifold. 99 percent of time, every time, a boost leak won't be in the manifold.

scotty nm35 Grand Master

scotty nm35

Posted
Posted

Quite often the leak only occurs when there is pressure in the pipe, such as a split in some rubber that closes when there is no boost. The best way to find it is a pressure test I have found, it's cheap and easy to do at home if you have a compressor.

denisonnd Apprentice

denisonnd

Posted
  • Author
Posted

Ok thanks.

I know sometimes turbo will work extra hard to reach its set boost when there is a small leak.

Can you have a situation where a car can reach its max boost and still have richer then normal afr at WOT(more black smoke)

In other words would you benefit from a wideband gauge in this case or it will simply show up as lower max boost on a boost gauge?

I have MAP sensor and take boost reading straight from the intake manifold if that helps.

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