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View Full Version : Hissing/whistleing from engine bay!!


Shifty
02-20-2007, 09:42 AM
This problem started all of a sudden for me.
the only thing that i can think of that happened was driving through the snow on my street, oversteering like crazy (+1 for free drifting!). I hit a few patches of ice chunks and after that i get a whistling/hissing sound from the engine bay.

I checked it by popping the hood and adjusting the throttle manually. the sound was coming from/near the brake booster, but i know that there are no really turning or moving parts that would make that noise, my brother (Protomor) noticed that a chunk of my intake mani gasket was missing!!
WTF!! i slapped some gasket maker around there until i could get a new gasket set in from the pelican parts. I let it set and tried it again, still the sound is there, but no change in the pitch or volume.

the next thing would be a vacuum line... they are old/original. perhaps goosing the throttle caused it to crack or separate??

my question is... and its a dumb one... where are the vacuum lines on the M20??

Dominic49
02-20-2007, 05:34 PM
vacume lin goes into the brake booster... the large one that is kinda hard to get to... if it is leaking just a little bit you will hear some whistling from it... and your brakes would be a harder to push....

Shifty
02-21-2007, 10:37 AM
i'll look into that later today, thanks for the info!

the brakes dont seem to be an issue however. perhaps over time, its gradually gotten worse and i havent noticed it.

chris325ix
02-21-2007, 03:17 PM
check the nuts that hold the throttle body to the intake manifold, and the intake manifold to the head. I had a similar thing happen to be after I put my stroker together, suddenly I was getting a really high pitched hiss/whine noise. turned out a couple of nuts had backed off a bit causing a tiny vacuum leak.

Shifty
02-22-2007, 09:04 AM
check the nuts that hold the throttle body to the intake manifold, and the intake manifold to the head. I had a similar thing happen to be after I put my stroker together, suddenly I was getting a really high pitched hiss/whine noise. turned out a couple of nuts had backed off a bit causing a tiny vacuum leak.

i'll look into that too. i tried to find the leak yesterday by having the engine running and moving vacuum lines around to see if the pitch would change or if the sound would stop... no go on that.

since my one of my intake gaskets is all sorts of busted up, that may be the problem. i did put some gasket maker around it but that doesnt seem to help.

chris, i plan on cleaning the intake up a bit so in the process i'll check the throttle body nuts. thanks for the tip!!

superj
02-22-2007, 10:13 AM
you can spray all the hoses with water, one at a time and when the hissing changes or stops, then you know the leak is right there.

Shifty
02-23-2007, 12:40 PM
you can spray all the hoses with water, one at a time and when the hissing changes or stops, then you know the leak is right there.

*hugs SuperJ*

colin86325
02-23-2007, 09:43 PM
A noise change suggests a vacuum leak. Most likely in anything that is upstream of the intake manifold.

87-325iC
02-24-2007, 11:16 AM
you need to really listen for it.

and if you are actually sure that its a vacuum/ air leak.. then try superJs water suggestion..
if you can hear the change in "air suckage" with the engine revving higher, this would tell you its air/ vacuum too.