Need help locating vacuum leak....

LJGriggs

Registered User
(Found It) Need help locating vacuum leak....

I have a leak somewhere in the vacuum system that I can't seem to locate. I can hear it when the boost guage is in vacuum. Sounds like a high pitched whistle. As I accelerate and vacuum goes to boost, the whistle changes pitch and gets quiet as the guage approaches zero. I am also experiencing some stumbling while in gear at idle (sitting at a traffic light, for instance). Also, when I turn the engine off, the whistle continues until the boost guage returns to zero. I have tried to locate the leak with my propane torch, but so far no luck. I thought I had isolated it to the lower connection on the intercooler, but after resealing both upper and lower, no change. I sprayed so much propane around the vacuum and supercharger fittings that I was almost ready to pass out. Never did hear an increase in idle. How long do you have to apply the propane to a leaky connection before the idle increases?
Anyone got any ideas of other places to check for leaks? I thought maybe it was the line connection on the boost guage, but the whistle is louder outside the car than inside....
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Well, the propane trick didn't provide any results, but I found the source of the leak. The upper flange stud nuts on the lower intercooler tube were loose (for some reason). I must have not gotten them tight enough when I replaced them after replacing the engine mounts. Cheap fix, just torqued them down, and no more leak.

Thanks for the help, guys!!!!
 
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IAC...

I am pretty sure that I have read where some guys had their IAC whistle when it went bad on them...But I have not exp. the exact scenario..Try unplugging it and see what ya get I guess...

Brad
 
Can't really say how fast the idle spead reacts to propane since I use starter fluid but I'd think propane would be pretty quick.

I read a post somewhere about a machine that can inject smoke into your vacuum system and you find the leak by looking for the smoke escaping... might want to call a few shops and ask about that.
 
Couple of ideas. If you did the propane test, the next thing I would suggest is you wait for the car to cool down and wrap every intake joint you can find with saranwrap. Including the MAF, TB, IC joints, SC collar nut, and rear intake tube. Then start it up and see if the whistle is still happening. You shouldn't have to run it very long and certainly not long enough to melt the plastic. If the whistle goes away, its one of those joints. If it stays then the problem is elsewhere.

The other thing I could suggest is if you can hear it constantly, take a cardboard tube as a stethoscope and see if that helps isolate the source.

If none of this works, reseal the other 2 joints and the SC top. If that doesn't work, start pulling every rubber hose near the back of the plenum and inspect them for brittleness and how well they seal.

Good luck.
 
I'm guessing it is a joint leak and not a hose leak (pin hole leak in a hose can sound the same though). Mine was doing the same thing a few months ago and I finally got it located to the lower IC tuber where it enters the inlet to the lower intake. My problem was that I did not tighten the mounting studs evenly when I resealed my engine. It did not happen at first, but would whistle very loud (seemingly) when it leaked. I tried the starter fluid, but there was not enough of a leak to cause the engine to rev up. I found the leak by using my hand to channel the sound. I readjusted the nuts on the mounting studs and the leak went away. No trouble since. When I had a vacuum leak (hose) it didn't whistle at all. Just a sucking sound. I'm guessing it is a very small leak like I had. The saran wrap idea sounds very good. I'd go with that only to add, if the sound stops, remove the wrap from one joint at a time until you isolate the joint. This is just been my experience with vacuum leaks anyway. If it helps, great, if not, that's ok too.
 
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