Full Boost then Low Boost?!

[TheCombover]

Recently my cars boost has been acting up. I have an MBC, so I unwound that so it was running actuator pressure and it was boosting to about 6-7 psi which was fine but then I wound in the MBC and it began to make another whistling type noise while under boost and not making anymore than about 7psi. I had hoped the MBC was the issue so I bought another one. The first time I boosted it. It went up to about 13psi totally fine but after that it was struggling to produce anymore than 2 or 3 psi and I can hear it spooling as well as another whistling which sounds like its losing pressure.

At first I thought it could be the actuator jamming open again but I have had a standard downpipe fitted so that shouldn't happen?

Could a boost leak cause this?!

[Peter Gidden]

Check every intake hose and clip for leaks.

[2mad]

No boost and extra whosh/whistling sound is a boost leak .. been there .

[TheCombover]

Awesome! Will have a little fiddle with the plumbing tonight.

[2mad]

Check the blow off valve is still air tight and not leaking too mate

[TheCombover]

What is the best way of doing this? Literally just rev my car and listen to every single bit of plumbing for leaks?

[2mad]

Yes listen for sounds that should not be there first .. Some use soapy water sprayed over the pipes and hoses and reving the engine ... me i would remove the pipes and hoses check for splits/leaks and reinstall . use your best judgement .. for the bov remove it and blow in to it .. it should be air tight

[2mad]

I had a bov fail years ago it was fine on idle but cracked open on boost .. like i said use your best judgement .. if you can cap off the bov for a test its worth doing .

[TheCombover]

I guess the bov is 23 years after all. Do you mean just block off the small vacuum hose coming from the bov?

[2mad]

No far more gross than that .. remove the bov from the hot pipe and blow with your lip forming a tight seal in to the valve .. if it leaks under lung pressure its screwed under boost .

[2mad]

No far more gross than that .. remove the bov from the hot pipe and blow with your lip forming a tight seal in to the valve .. if it leaks under lung pressure its screwed under boost .

I did this test on my badly running car and it failed miserably ... fitted a hks valve and sweet

[TheCombover]

I will give that a go!
Will be nice if the cause is somthing simple like the bov!

[TheCombover]

Or I could run the car without the bov connected? If it boosts normally then the problem is the bov itself?

[2mad]

Or I could run the car without the bov connected? If it boosts normally then the problem is the bov itself?

Yep as long as its capped off that will work bud

[TheCombover]

Do i need to cap off the bov itself as well?

[androo007]

Can a leaky bov cause irratic boost spikes / levels then? I Always wondered. It assumed you would just have lower boost levels.

[2mad]

Do i need to cap off the bov itself as well?

If you have a stock bov fitted to the hot pipe im not sure how you would remove it and cap off the hot-pipe .. you could try removing the vacuum line from the valve and capping it off then and capping off the hose leading back from the bov to the intake hose , that should give an air tight seal stopping the valve from leaking (if it leaks) for a test run.. out side the box thinking but could work. i would try the blow test first

[2mad]

Can a leaky bov cause irratic boost spikes / levels then? I Always wondered. It assumed you would just have lower boost levels.

A leaky bov will ether course your turbo to have to work harder to make boost or course it to fail to make boost .

[2mad]

How you getting on mate .

[TheCombover]

I found a boost leak. One of the intercooler pipes had a broken jubilee clip. Causing a massssssssive boost leak! I sorted that. Still has a boost leak. Which i can hear. When it doesnt boost it makes a tsssshhhhh type noise and makes about 5 psi. Sometimes it reaches full boost.
Going to take the bov off tonight and try the blowy trick.

Getting frustrating