Boost Hiss

[John Sims]

I thinking of throwing out my Boost guage as I no longer need it. I now seem have an audible boost monitoring system. When going to +VE manifold pressure I get a hiss which increases with boost.

The guage still reads and maintains boost pressure but I obviously have a leak somewhere.

Daft as it may be the noise seems to be comming from the air vents and is more pronounced when directed at the windscreen. I think this is just coincidental though as my new dump valve noises come from the same place and that obviously isn't located behind the dash - unless what I think is dump valve noise is actualy the effect on the air flow from the leak. I have a new non-recirc dump valve (Bailey DV24), which isn't quiet, so I am assuming it is the dump valve I can hear.

Does anyone know of an effective way of leak testing vacuum lines? I was wondering if there is a system of pressurising the pipes and passing smoke down them to demonstrate the leak.

I guess another way could be to remove the pipes from the inlet manifold and connect them to a foot pump to see where the air comes out. Is this likely to damage anything (valves, diaphragms etc)?

 

[Mark_Bennett]

ORIGINAL: John Sims

I now seem have an audible boost monitoring system.

I thought that you were going to say "the wife"[]



Sorry for the non-helpful reply[&o]

 

[John Sims]

I thought that you were going to say "the wife"

No, but she was very anoying when I took her out in the car this morning. While I wanted the enjoy the "gwooosssssh" sound of my new dump valve, she kept immitating it and spoiling the moment. It's going to be even worse with Peter in the car as well. []

 

[Diver944]

I saw a post on Rennlist recently where a bloke (sorry, a guy) had pics of an adaptor he'd made to connect to the hard pipe coming from Turbo to the intercoolerto do this exact same test.

I'm thinking you could take off the elbow pipe that goes from the dump valve to the intercooler pipeand put a rubber bung in there with a hole in the middle attached to a foot pump with a gauge. Then pump to 15psi and listen. As long as you don't go over 15psi I think you'd be fine as thats what the Turbo does anyway.

This does sound very suspicious with your new dump valve though [&:] Have you tried the old one back in and just rely on Belinda and Peter for the 'gawooooooshing'

 

[John Sims]

This does sound very suspicious with your new dump valve though

It was doing it with the old one. I was hoping that the new one would cure it. []

I did wonder about pressurising the inlet manifold via one of the pipes - a spare T and an alternative piece of Pursil on one of the lines should do it. I could get realy clever and use a valve from an old bicycle tyre to retain the pressure [8|]

 

[944Turbo]

Go on then! [] or the banjo bolt might be a good place to connect I think the vacuum lines are all on the other side of the throttle valve so might be worth checking both.
Tony

 

[John Sims]

Go on then!

I did. It doesn't work.

For a start the air filter needs to be blocked as otherwise all the air escapes the wrong way. [] Then there is the brake servo?

I picked a few individual lines, or obvious closed loops and tested them:-

The line to my boost gauge seems OK - this also links to that little plastic valve on the brake servo line. - [FONT=Times New Roman"]I checked it again - it doesn't go to that little plastic valve it goes to the fuel vapour purge.

I also checked the T'd line from the banjo bolt to the manual boost controller and waste gate - this seems to blow to atmoshere, is that right? Could this be the culprit? - [FONT=Times New Roman"]This was playing on my mind so I checked it again. I lied. It doesn't blow

There are three vacuum elbows and pipes on the bulkhead behind the engine, obviously to do with the heating - why does Porsche have to make everything so complicated. As these are linking onto a bulkhead connection they must go somewhere under the dash - However, I pulled the pipe off the pressure reservior, that also links into the heating pipes, and this was holding a charge so, again, I'm assuming it must be sealed.

 

[944Turbo]

talking of audible boost click here
Tony

 

[John Sims]

talking of audible boost click here

That's just silly.

I've got to admit to being a little disapointed, having just fitted my Bailey DV24 to find they now do a DV34 with a trumpet - now available in the new Demon Tweeks catalogue and good Chavs'r'us outlets.

 

[Chris Goodman]

'Hissing' on my Turbo turned out to be perished cap on the vertical pipe at the rear of the engine (left hand side when viewed from the front) that I believe a diagnostic sensor can be attached to.

 

[John Sims]

Mr Cannell and I spent a happy hour or so bunking off work and cruising round in Beaky this afternoon looking for hisses, amoung other things.

Mr Cannell's prognosis - It isn't a hiss it is the noise from the induction kit. So I feel silly then.
I did cure the hiss yesterday while on the way to Stan's Shed airport at 5:00 in the morning. I had just decimated a Peugeot that cut me up at a roundabout. Beaky left him as a tiny speck in my rear view mirror, following two massive exhaust flames on the upshifts []. Several miles down the road I blew off an intercooler pipe. The hiss stopped but I was left driving a low compression Lux. It still took Peugeot ages to catch me though []

Note: For Turbots without MAP, MAP lets you carry on driving smoothly, though somewhat down on power, if you blow an inlet pipe. This isn't the best thing to do in the long term as, obviously, you are sucking in unfilltered air. You don't have to pull over in the dark after passing Peugeots though.

 

[John Sims]

I've found my leak. By employing the 2TA (patt applied for) leak finding kit I now know where the leak is.

For those that don't want to pay for development, the kit includes 2 laytex gloves (one with the end of finger cut off) a length of hose, some rubber bands, and a cigar (or two in this case).

1. Push a hose through the finger hole in cut laytex glove.
2. Put the complete laytex glove over the exhaust. (use a rubber band to seal if you have a limp small bore exhaust)
3. Put the hose and glove combination over the inlet pipe again use rubber bands to seal as necessary.
4. Light cigar and blow smoke down the tube pinching the glove finger to hold pressure as necessary.
5. Look where smoke comes out.

Difficult to believe but it works! However....

Good News - I now know where the leak is.

Bad News - It took two cigars to do it and I am now swinging back an forth from feeling as high as a kite to as sick as dog. [8D][:'(][8D][:'(][8D][:'(][8D][:'(]

Bad News - I bought £100 of pipes to solve the leak problem and it wasn't any of them.

Good News - I haven't paid Rick for any of the pipes yet.

Bad News - The leak is under the inlet manifold on one of the idle stabilizer pipes (that might account for our odd idle levels Rick).

In summary ......buttocks! []

 

[Diver944]

John that's just about the worst place to get to [], you need to find a friend with really small hands.

(though I doubt you have many friends when they see that picture)

 

[John Sims]

John that's just about the worst place to get to , you need to find a friend with really small hands.

I'm training mice as we speak. []

 

[eastendr]

ORIGINAL: John Sims

Good News - I haven't paid Rick for any of the pipes yet.

Good News - I know where you live [>:][>:]

Bad News - you might fend me off by throwing my G-Tech RR at me [][]

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