How Do I Find The Leak? - BMW Forum

Ferrahs · 01-09-2005, 11:49 PM

Its a 1996 328 and I know theres a vacuum leak, the symptoms are there...The infamous hissing noise, lack of power, etc. Now my issue is where is it, none of the hoses seem bad. The hissing noise is coming from the vicinity of the manifold which worries me cause that is not an easy job. I was also thinking the throttle body because when you rev the engine slightly the hissing noise goes away, but thats usually normal with all vacuum leaks( its either that or the engine dies) but whats peculiar about this one is that you only have to slightly rev it like only to 1200 rpms nothing high for the hissing to go away...What i wanna know is, am i missing or overlooking anything. Its perpexing because ive never heard a case where it comes from the manifold area but then i could be wrong.. Has anyone had experiance with this that can be of help please.

Rooz · 01-09-2005, 11:57 PM

Quote:

Originally posted by Ferrahs@Jan 10 2005, 12:49 AM
Its a 1996 328 and I know theres a vacuum leak, the symptoms are there...The infamous hissing noise, lack of power, etc. Now my issue is where is it, none of the hoses seem bad. The hissing noise is coming from the vicinity of the manifold which worries me cause that is not an easy job. I was also thinking the throttle body because when you rev the engine slightly the hissing noise goes away, but thats usually normal with all vacuum leaks( its either that or the engine dies) but whats peculiar about this one is that you only have to slightly rev it like only to 1200 rpms nothing high for the hissing to go away...What i wanna know is, am i missing or overlooking anything. Its perpexing because ive never heard a case where it comes from the manifold area but then i could be wrong.. Has anyone had experiance with this that can be of help please.

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This mind sound stupid, but my mom had a somwhat smiliar problem on her 1997 540, and it turned out it was just a dirty (greased up for some reason) air filter.

Ferrahs · 01-10-2005, 12:00 AM

Thanks for the suggestion but i checked that and unfortunatly its not the air filter, you can hear the leak, its just a matter of finding it.

Speedy-325is · 01-10-2005, 02:58 AM

get a can of starter fluid (BEST) or even wd 40 and LIGHTLY MIST (not spray!!!) but mist the areas you suspect and the hoses while the engine is idling. when you mist the area that does have a leak, the rpm's on your car will rise for a second cuz its pulling in the spray and burning it as extra fuel. you wont need to spray alot, but this is the best way to find it if it is there.

Mark

fredo 328 · 01-10-2005, 08:35 AM

vent pipe tight at the connection with valve cover? maybe there is a leak along this system which would be an easy fix, and be the cause of the hiss and bad idle.

thekid · 01-10-2005, 09:44 AM

but you do not have a bad/rough idle correct?

kyle_baker · 03-29-2005, 01:21 PM

i have a problem fairly similar, when i start my car after letting it sit over night i hear a squeeking noise sometimes, when i take the rpms up to alittle about 1000rpms it stops squeeking, but when they fall below again it squeeks, the noise goes away once the car has warmed up to running temps but its really annoying. I'm thinking it may be a loose fan belt or something but haven't looked close yet, any suggestions?

oh yeah, my idle is kinda rough when first started, like bouncing from 500-900 until it warms up. sometimes if you rev it a few times after starting it the idle smooths out alittle.

anyone?

kyle_baker · 03-29-2005, 07:31 PM

anyone?

3serbmdubya · 03-29-2005, 08:33 PM

that squeak could be your pulley on the alternator. while its running just spray some wd-40 on it (the pulley) and dont worry it wont harm your alt because wd-40 is electronics safe and squeaking should go away. otherwise i'd say its your belt

kyle_baker · 03-29-2005, 09:08 PM

ok, i'll try this tomorrow and let you know how it goes

kyle_baker · 03-30-2005, 06:19 PM

well sprayed the pulleys, think it helped alittle, we'll see as time goes by.

NeverLeaned · 04-01-2005, 06:36 PM

First, A question..... Why use starter fluid for this test??? All I keep thinking is its the equivlant of pouring gas all over your hot engine

Now the "easy" vaccum test. Grab some vaccum tube from your local autoparts store (you can even use some of that fish tank hose for testing)

Remove on end of the hose from the car, trace out where it goes and remove that end too.... then in its place use the hose you bought at the autostore. (Don't route it nice and neat) Your gonna repeat this process with each hose until your troubles disappear....... then replace the bad hose.

Shouldn't take more then 30 minutes to test every hose.

Good luck
NL