tricks to find vacuum leak

fiveohpatrol · 09-29-2002, 11:13 PM

I have a vacuum leak from hell

I know it is coming from the front of the intake, but I can't (nor can 3 other guys) seem to be able to find it.

I've tried spraying carb cleaner around there and it doesnt change the idle one bit.

Its also an intermittent leak, it will leak for about 5 seconds, then shut off for a few seconds and then come right back.

My brakes seem to be a little harder to push, but I havent put a gage on it to see how much vacuum I am getting.

Is there any other way to find this leak?

If I can't find it, I'm just gonna pull the upper intake off and replace all of the vaccum lines at once.

MDM · 10-03-2002, 01:38 AM

A proven way of finding a vacuum leak is using a propane torch. Turn the torch valve on but do not light it and move it around the suspected leaking area. When your idle rises, you have found the leak. You have to be careful, though, as using propane on a running engine is not without risk. If you have a plug grounding to the block, bad wires, etc. this is definitely not recommended. Fix any electrical problems first then give the propane a try.

Jthompson · 10-03-2002, 01:52 PM

that sounds safe!!! although i have heard that quite a few times. Try this:

Take a section of tubing, or rubber heater hose. Put one end to your ear, take the other end and point it at places around the engine. The tube acts like a doctor's stethascope, and magnifies the vaccuum leak sound when you get close to it.

LX XLR8R · 10-03-2002, 02:11 PM

dont take thi sthe wrong way but 1st your positive its not the ac compresser tunring on???

this said a slit in a line such that when the vacuum builds up it it opens but then closes on itsself after it relases is a possablility..other than that im stumped if it is a leak..one more shot in the dark is a leak on the IAB so when it opens it leaks???just a random thought

fiveohpatrol · 10-03-2002, 03:56 PM

Quote:

dont take thi sthe wrong way but 1st your positive its not the ac compresser tunring on???

LOL, i'm pretty dumb, but not that dumb

even if I was, it wouldn't be it, because i no longer have AC

I know it is a vacuum leak for three reasons. I can hear it. My brakes are harder to press. And I have too much fuel pressure at idle.

I'm stumped. I think I'm just gonna replace all the lines under the upper intake and see if that does it. I sure hope so, because it is causing a lean condition and hesitation in the mid RPM range (verified by my AF graph from a recent dyno session)

bigblockcoupe · 10-03-2002, 06:15 PM

as jthompson said get a length of heater hose and put it to your ear you will be able to find the leak easily.

09-29-2002, 11:13 PM	#1
fiveohpatrol I'd rather be basketweaving Join Date: Feb 2000 Location: Indianapolis Posts: 2,551	tricks to find vacuum leak I have a vacuum leak from hell I know it is coming from the front of the intake, but I can't (nor can 3 other guys) seem to be able to find it. I've tried spraying carb cleaner around there and it doesnt change the idle one bit. Its also an intermittent leak, it will leak for about 5 seconds, then shut off for a few seconds and then come right back. My brakes seem to be a little harder to push, but I havent put a gage on it to see how much vacuum I am getting. Is there any other way to find this leak? If I can't find it, I'm just gonna pull the upper intake off and replace all of the vaccum lines at once. __________________ NMRA O/C 9516 NA pumpgas stickshift 347 10.65@125.6, 6.73@100, 1.41 60ft

10-03-2002, 01:52 PM	#3
Jthompson Registered Member Join Date: Sep 2002 Location: Corona, Ca. Posts: 80	that sounds safe!!! although i have heard that quite a few times. Try this: Take a section of tubing, or rubber heater hose. Put one end to your ear, take the other end and point it at places around the engine. The tube acts like a doctor's stethascope, and magnifies the vaccuum leak sound when you get close to it. __________________ Jeremy 1986 Mustang GT Convertible 1972 2 door 302 Maverick 1994 POS head gasket clubbed broke down T-bird with $6000 left to pay off

10-03-2002, 02:11 PM	#4
LX XLR8R Dirk Diggler Join Date: Feb 1999 Location: SLOATSBURG, NY Posts: 1,931	dont take thi sthe wrong way but 1st your positive its not the ac compresser tunring on??? this said a slit in a line such that when the vacuum builds up it it opens but then closes on itsself after it relases is a possablility..other than that im stumped if it is a leak..one more shot in the dark is a leak on the IAB so when it opens it leaks???just a random thought __________________ 95 undecided cubes, AFR 185s,undecided cam, undecided intake, and a 150 hit 89 "turbonotch" 2.3T You might want to hold on..i saw this on a cartoon once

10-03-2002, 06:15 PM	#6
bigblockcoupe Registered Member Join Date: Aug 2002 Location: broken arrow Posts: 212	as jthompson said get a length of heater hose and put it to your ear you will be able to find the leak easily. __________________ Rice Haters Club member #68 '93 Cobra 10.20@135 '89 Gt Coupe 12.20@115

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10-03-2002, 01:38 AM	#2
MDM Registered Member Join Date: Feb 2000 Location: Flemington, NJ USA Posts: 166	A proven way of finding a vacuum leak is using a propane torch. Turn the torch valve on but do not light it and move it around the suspected leaking area. When your idle rises, you have found the leak. You have to be careful, though, as using propane on a running engine is not without risk. If you have a plug grounding to the block, bad wires, etc. this is definitely not recommended. Fix any electrical problems first then give the propane a try.