Best Method For Finding a Vacuum Leak?

[kimokalihi]

I think my 98 Chevy Metro 3.0 has a vacuum leak. Inside the car I can hear it whistle and it changes with engine RPM. But under the hood I can't hear a thing.

I tried spraying a mist bottle of water all over the engine and didn't hear any change in rpm. Should I try propane or something?

I know it's affecting the MPG or performance or something and it's annoying.

[Kelly]

Brake cleaner will want to kill it, and is non flammable (and just might remove some of those unsightly stains)

Or get your smoker friend to blow into the intake?

[kimokalihi]

Isn't brake cleaner bad for rubber and plastics?

[magicmike]

check this out

http://bbs.legacycentral.org/viewtopic.php?p=300724

Also, its carb cleaner thats used not brake cleaner. That is also posted somewhere in here. Spray it around the engine bay and listen for rpm changes.

[kimokalihi]

I'll try the carb cleaner then.

While reading that thread I noticed this. I didn't think an exhaust leak would whistle but I guess that's a possibility. I know for a fact that directly below the shifter the exhaust pipe has a small crack in it. Maybe that's whistling?

I had a whistle on acceleration that I couldn't figure out. No vacuum leaks or issues. Turns out it was the muffler. Replaced the muffler and no more problems.

I can't say that's the same issue as you guys, but something to think about. I ended up finding it when I had a friend stand outside the car and listen while I revved it up.

[206er]

you can also look for the obvious stuff if you havent already or have no luck with the carb cleaner(or starting fluid).
check all the vacuum lines for damage/disconnected/loose
check torques on manifold bolts(this has worked for me before)
any cel?

also what some pro mechanics will use is a smoke machine that lets out a tiny plume of smoke that gets sucked around by the vacuum leak so you can see it. some burning string or stick of wood or something? never tried that, just thinking out loud.

[kimokalihi]

Good ideas! No CEL. I've never seen the CEL come on once since I'm owned this car and I've put 40K miles on it I think. Awesome car, I might add. As much as I get made fun of for driving it, it's the shit. I highly recommend buying one for fuel economy, ease of parking, emissions(save the world or whatever) and they're cheap.

[bushlocos]

I use a length of hose. Put one end to my ear and move the other end around until I find the noise I'm looking for.

[kimokalihi]

Found the vacuum leak! It was coming from my subwoofer.

Alternator whine is the correct term. I swear it sounded like the sound was coming from the engine bay. It sounded like it was coming from directly around the area of the intake. But that explains why it was not audible from outside the car or with your head down in the engine bay.

It's not coming from my speakers, just the sub. Which means that it almost has to be coming from the RCA cable for the sub only. And those RCA cables only run a short distance from my audio processor in the hatch to my amp which is about 6" away. But it's not done, it's just thrown in there fire hazard style so the amp cables are also in the same place and I'm sure the sub RCA cable is probably sitting right on the power cable.

I'll look at it sooner or later.

I confirmed this by listening to the subwoofer with my ear about 3" away from it and then turning my stereo off and the sound instantly disappears. Turn it back on and there it is again. Push pause and it's still there, volume has no effect on the audible level of the alternator whine.

I hate alternator whine. I usually don't have it but then again I usually don't throw all my shit together in the back of the car and then never finish it.