Baffled by this boost leak...

[alias747]

OK this is seriously pissing me off... I have had some sort of boost leak issue going for about 4 months now. I have been so busy lately that I haven't had much of a chance to look at my car at all. But this is kinda what is going down:

I hear a high pitch whistle at about -10 to about 0 when I push the gas a little. By the time it goes over 1 and into the boost range it sounds like a bunch of air is leaking somewhere. My car acts pretty hesitant and boosts really low, if I lay it down it MIGHT see 15 psi but still feels really weak. If I lay down the accelerator while in vac it will go to 0 and build boost VERY slowly and then just sound like crap with air leaking out and be really weak.

Now before you guys start yelling at me to PRESSURE TEST!!!!!!!!, listen---- I HAVE!! 4 times! I just did again tonight and I found 2 VERY small leaks in my intercooler hoses, nothing that would be a big deal compared to the amount of air I seem to be hearing.

I had thought it possibly was my MBC becuase the last time I pressure tested a bunch of air was coming out of it. People told me it was normal, but I wanted to test to be sure, I put the N75 back in and same issue. It's a bit smoother with just the N75 in but still same issue.

So thats pretty much the situation, I have been banging my head against the wall with the issue for a long time. If you need anymore information please ask, I must get to the bottom of this! I have had to drive my car like a grandma for pretty much most of the summer becuase of this and that makes me sad. Of course I haven't driven it a ton this summer anyway but you know what I mean!

PLEASE PLEASE PLEASE HELP ME FIGURE THIS OUT!!!

[MacDaddy]

I would try some sort of repair even if its half-assed, on the two small leaks you've found just to see if it makes a difference, if it does, perhaps they are more of a problem than you think.

[alias747]

I would try some sort of repair even if its half-assed, on the two small leaks you've found just to see if it makes a difference, if it does, perhaps they are more of a problem than you think.

I did fix those leaks, sorry I guess i should have said that but I figured most people would assume I would fix the leaks.

The sound SEEMS like it is coming from the right side of the engine, but sound could be playing tricks on me.

[quickaudi]

go back over every one of those connections

check the o-ring around the hard piping for the inlets of the turbos

check all those IC hoses again, get better hoses and clamps

pull the TBB completely off and inspect it all over

reclamp everything

how new are DVs?

[alias747]

go back over every one of those connections

check the o-ring around the hard piping for the inlets of the turbos

check all those IC hoses again, get better hoses and clamps

pull the TBB completely off and inspect it all over

reclamp everything

how new are DVs?

I checked all the inter cooler hoses about 3 times, no signs of leaks under pressure after i tightened those 2 connections.

My TBB is silicone and is very tight, no leaks, Ive looked.

I mean if there isn't any noise of a leak under a pressure test how the heck is there one when I'm driving?? The only thing on your list that makes me nervous is the o-ring that you are talking about. With my luck it would probably be something way in the engine like that, thats impossible to get to...

[MacDaddy]

I just thought of something, when my friends Jag developed a vacuum leak after the MAF sensor and before the supercharger it took forever to accelerate, a little bit like what sounds is happening with your car.

certainly dosn't hurt to have a look.

[saucys4]

It is probably the DV's. I had mine go out and had similar issues. Also check the crappy braided vacuum lines going into them.

[alias747]

I just thought of something, when my friends Jag developed a vacuum leak after the MAF sensor and before the supercharger it took forever to accelerate, a little bit like what sounds is happening with your car.

certainly dosn't hurt to have a look.

My vac reads at perfect levels, when its warmed up it sits right at 20-21.

It is probably the DV's. I had mine go out and had similar issues. Also check the crappy braided vacuum lines going into them.

I can check them again, I haven't in a while. I guess I haven't heard of many 710n's going bad. I suppose that if the DVs weren't working right it might make sense that they don't leak air during a pressure test but when driving they act up.

Could a faulty n249 valve cause weird issues like this?

IM OPEN TO ANY IDEAS!

[exorcet]

pressure test and spray EVERYTHING down with soapy water and look for bubbles. it might not be a bad idea to take the front bumper off and spray the intercoolers too - just to make sure.

have you scanned for non-cel codes that might be there like EGT related, etc?

[alias747]

pressure test and spray EVERYTHING down with soapy water and look for bubbles. it might not be a bad idea to take the front bumper off and spray the intercoolers too - just to make sure.

have you scanned for non-cel codes that might be there like EGT related, etc?

Yep I have scanned for codes, just last night even. The only thing I get is O2 codes becuase of my piggies and a couple misfires every once and a while.

I understand what you are saying about pressure testing and soapy water, but really from how much boost Im losing don't you think I would be able to hear it when I pressure test? And the fact I can hear it quite audibly when I'm driving? This is leading me to believe that it is some kind of fault somewhere else like the dv's or something. But I know I could be wrong.

[alias747]

Bump...

[highPSI-S4]

My issue is somewhat simliar to yours, i've done everything also to find the leaks, i also hear air somewhere in the rear but couldn't find the leak. I'm thinking it was just the MBC. I'm replacing the frount mount with stockers and getting EBAY ASI hoses. Hoping that will fix the issue.
Could it be DV's. If they leak wouldn't you hear the air coming out of them?

The only difference i see between us is that you see 20-21hg at idle and i only see 15-17 at idle.

hope you find out what it is.

[exorcet]

Yep I have scanned for codes, just last night even. The only thing I get is O2 codes becuase of my piggies and a couple misfires every once and a while.

I understand what you are saying about pressure testing and soapy water, but really from how much boost Im losing don't you think I would be able to hear it when I pressure test? And the fact I can hear it quite audibly when I'm driving? This is leading me to believe that it is some kind of fault somewhere else like the dv's or something. But I know I could be wrong.

if you're running a 'standalone' MBC (i.e. with bleed hole) that will make an audible 'pssssshhhh' bleed sound for sure.

DV's would be another thing to test. Definitely an item that could 'bleed' but you wouldn't hear in a pressure test.

[JDM EJ1 95]

i had a similar issue.. and it was a vac hose near the Fuel pressure regulator.. it sounded liek a ton of air was leaking on the pass side.. but it was echoing or somthing and it was really leaking from the vac line over there.. there are some with like braided cloth shielding over them.. i had to replace a few cause they were in bad shape.

check it out.

same thing tho.. it hought i heard air in the rear.


easiest thing to do tho.

take a can of brake clean.. star the motor up.. and spray it everywhere you can think there could be a possible vac leak... once you find it themotor will die out when you spray the brake clean on the busted hose/valve/etc.

easy diagnosis

[NogaroWonda00]

ive had the same thing happening to me lately and i thought it was the dv's replaced them. then the spark plugs because of a miss fire code, and i pressure tested the shit out of mine didnt hear any hissing or anything yet when i drove it sounds like i have a massive turbo and no power. then i took the f shaped hoses off and found a huge split in it. i too ordered the asi hoses and hopefully it fixes it lol

[alias747]

ive had the same thing happening to me lately and i thought it was the dv's replaced them. then the spark plugs because of a miss fire code, and i pressure tested the shit out of mine didnt hear any hissing or anything yet when i drove it sounds like i have a massive turbo and no power. then i took the f shaped hoses off and found a huge split in it. i too ordered the asi hoses and hopefully it fixes it lol

Did you already have a Samco f-hose and that split or were you still on the stock one? I have a Samco and I thought that it was supposed to be able handle just about anything. I take it that when you pressure test the pressure doesn't reach to where the f-hose is? That's an interesting finding because that sounds exactly like what it might be for me!

[highPSI-S4]

Did you already have a Samco f-hose and that split or were you still on the stock one? I have a Samco and I thought that it was supposed to be able handle just about anything. I take it that when you pressure test the pressure doesn't reach to where the f-hose is? That's an interesting finding because that sounds exactly like what it might be for me!

Also on a second note you should also try to inspect your spider hoses.
I ruled mine out only cause there new but it could cause problems.

And that sound nogarowonda00 id describing is a sound similar to a bad f-hose and/or TBB both of which i replaced.

[MacDaddy]

easiest thing to do tho.

take a can of brake clean.. star the motor up.. and spray it everywhere you can think there could be a possible vac leak... once you find it themotor will die out when you spray the brake clean on the busted hose/valve/etc.

easy diagnosis

good call, but a cleaner method would be to use a can of propane (unlit) and use it to find a possible vacuum leak, if there is a leak present, the propane will be sucked into the intake and increase the engine revs.

[MacDaddy]

My vac reads at perfect levels, when its warmed up it sits right at 20-21.

that only means there are no leaks in the intake manifold, it does not indicate if there are any leaks between the maf sensor and the throttle butterfly.

[alias747]

that only means there are no leaks in the intake manifold, it does not indicate if there are any leaks between the maf sensor and the throttle butterfly.

Would that really affect my boost though? And how much vacuum is really created at the MAF?

[NogaroWonda00]

no i didnt have the samco hoses just stock ones, mine aren't is such good of shape either, they are almost dry rotted in some spots.

for me when i ease into it its fine, but WOT its fine untill full boost then i just loose a shit ton of power. so thats why i think it maybe the same for you.

i dont think it sounds like you have a vac leak and no you wouldnt feel a huge power loss from what i found or at least not from what ive came across.

im not sure if pressure does go to the f hose or not when testing it. even when i had it up to like 35 psi testing it no hissing but i took it off and found a huge split. maybe it has to do with heat or something cause i still dont get why technically im running higher psi and its not splitting, but when i hit full boost it goes psssssssshhh.

ive also talked to a shop in denver and they said they dont usually do upgraded hoses on stage 3's and have only had one case where one did leak. it is very baffling though lol

[lrg8683]

have you physically removed and checked your TBB and Fhose?

[S4-ORCE]

check the o-ring around the hard piping for the inlets of the turbos

This isn't pressurized, it wouldn't make a difference no?

[gointoscott]

Hey bro,
I keep forgetting to mention to try measuring block 115 on vag-com and compare requested boost to actual boost to see the difference for boost leak.

maybe monday youll have time to check it

[MacDaddy]

Would that really affect my boost though? And how much vacuum is really created at the MAF?

if there is a leak, the engine has no idea what the actual amount of air coming into the engine. on the audi i'm not sure specifically how this would affect the car, but on other cars that i've worked on that had a leak between the maf sensor and the throttle, the cars had very slow throttle response. it may very well affect boost levels too.

[quickaudi]

This isn't pressurized, it wouldn't make a difference no?

you'll still have an intake leak, and you'll hear it on pressure test, duh

[S4-ORCE]

you'll still have an intake leak, and you'll hear it on pressure test, duh

I meant, make a difference as in affect boost.

[Caddy7]

Have you fixed the problem? What was wrong?

[noclutch]

Ended up being the N249 or the N75, I bypassed both and it seems fine. I bought this car BTW.