vacuum leak I'm gonna shoot it!

[monkeydude3]

Hey all~
I have a 1994 XL... 4.0L OHV. Vacuum leak!! It idles at about 900 rpm, when usually it idled at 650/700... so I know it's a slight leak causing it just to run a little faster. I hear a hissing that sounds like IT COULD BE coming from under the intake... but I'm not sure. I checked every line that comes off that little pod on the back of the upper intake, there are about 5 vacuum lines that tie into there, they all check out. I still hear a nice hissing when it idles that only sounds like a vacuum leak... Any ideas or suggestions or tips for finding this damn leak?? take care!

GEORGE

 

[heyok]

I had a vacuum leak that my mechanic friend found by using a propane torch. He turned on the propane gas a little bit (didn't light it of course!) and moved it around various parts of the intake until he heard the engine idle differently. There was a tiny hole in the intake tube that we pluged up with some silicone.

I'm not suggesting that you try this because it sounds dangerous now that I think about it!

 

[monkeydude3]

hm, not a bad idea... I tried spraying carb cleaner all over in the same fashion and usually that will make it either rev up or sputter and I got nothing

 

[Eneurb]

Propane enrichment is a great way to locate a vacuum leak. Especially if you can rig up a hose that will concentrate where you will direct the propane. You proably have leaking fuel rail, upper intake plenum or lower intake gaskets... or all of the above.

 

[urbanistic]

If you are looking into the engine compartment, look to the upper right, past the res for the anti-freeze and washer fluid. There is a vacuum tube that has a type of filter inline. This comes apart and causes your problem. you can trace one side of the line there from the vacuum dist. point on the right top of engine.

 

[monkeydude3]

what do you mean comes apart? As in the two vacuum lines become separate? because i'ts all still connected there

 

[urbanistic]

Coming off of the idler control? I believe its called. Go north from your anti-freeze and go past the purge canister, the thing with 2 round caps on it. Its the next component there... has a line going to your throttle control and a vacuum tube on top and on bottom. The one on top is going to run to the vacuum dist. point/tree. Between this spot and your vacuum tree, in line, is some type of component... possibly a regulator or filter. Is not attached to anything and disc-like. The tubes here get oily and fall off of this component. This causes a rough idle. The tub can fall down somewhere and may look as if its going somewhere but it isnt. Does that help?

 

[geber11]

Had the same problem where the vent was stuck on defrost. Just looked under the hood looking for the vacuum lines and sure enough when I pulled on the one that lays across the top of the motor near the oil filler cap with the connection in the middle of it, one end was not connected. The line is black in color until it gets to the connector then it turns red. The loose end is supposed to go into the top port of the vacuum canister (round black toilet ball), well it wasn't, it was just hanging there. So, I reconeccted the line to the canister and now the vent selection works perfectly. The line doesnt feel very secure in the port, it may come off again. Maybe I'll try taping it or something. Once again explorerforum save me money, Thanks to all who contribute here.