Help Me Find My Vacuum Leak

[maximos]

Symptoms started a couple weeks ago and are as follows:

1. AC mostly going through defroster vents, but will occasionally switch back to regular vents.

2. If I shift into neutral and coast to a stop the RPMs will hover around 1800rpm and eventually go down to normal.

3. When idling the engine will suddenly switch to a different sounding idle pattern - doesn't sound normal.

It's not a question of IF I have a vacuum leak, it's WHERE is the vacuum leak? Are there any common places I should know about? Any type of test I can perform to help hasten the process? I'm pretty inexperienced with hunting for leaks in the vacuum system so I'd be extremely greatful for any advice you veterans of the art could provide.

Thanks in advance,
Andrew

 

[79'293stang]

Spraying carb cleaner of wd40 in the engine bay slowly over certain areas can often help. just spray until you hear your engine raise in rpms and then you can start to narrow it down!

 

[maximos]

Spraying carb cleaner of wd40 in the engine bay slowly over certain areas can often help. just spray until you hear your engine raise in rpms and then you can start to narrow it down!

I'm not exactly sure I understand the reason behind this. Are you saying that WD-40 entering a vacuum line will cause the engine to raise it's RPMs - thus showing where the leak is?

 

[Adam95GT]

For the vents.... check the tube that comes out of where the ac passes through the fire wall... follow it to the vac tree (drivers side or engine bay in the back next to the fire wall.) and check for leaks... if none on that tube check the other tubes on the vac tree...


yes if you buy some carb cleaner and spray it around the vac leak will suck it up and you will hear a "rev".

 

[maximos]

if none on that tube check the other tubes on the vac tree...

I guess my biggest problem is that I don't know where vac tree is. From what I've read, the majority of vac lines are hidden in the fender. I've inspected the vac lines I can see in the engine bay, but I've only found one suspect on the passenger which, of course, leads into the fender. Should I be looking behind the intake manifold?

 

[Adam706]

Symptoms started a couple weeks ago and are as follows:

1. AC mostly going through defroster vents, but will occasionally switch back to regular vents.

2. If I shift into neutral and coast to a stop the RPMs will hover around 1800rpm and eventually go down to normal.

3. When idling the engine will suddenly switch to a different sounding idle pattern - doesn't sound normal.

It's not a question of IF I have a vacuum leak, it's WHERE is the vacuum leak? Are there any common places I should know about? Any type of test I can perform to help hasten the process? I'm pretty inexperienced with hunting for leaks in the vacuum system so I'd be extremely greatful for any advice you veterans of the art could provide.

Thanks in advance,
Andrew

i had the same problem with the air stuck coming out the defroster vents. there was a small thin air line that ran along the firewall up top and behind the motor. that line was cracked.
this might be the line Adam95GT was referring to also.

 

[Adam95GT]

Ok here we go....

Follow the green line... it comes out of where your ac goes in the fire wall... and goes to the vac tree shown with the expanded box.

 

[maximos]

Ok here we go....
Follow the green line... it comes out of where your ac goes in the fire wall... and goes to the vac tree shown with the expanded box.

That's where I've been looking for a few days now. The hose looks great going into the vacuum tree. I will follow it and see if it shows anything else. Thanks for everything so far!

 

[maximos]

WOW - It was right in front of my eyes the whole time. The smallest hole you could imagine in the line. Thanks for everything. This got me thinking about some things though. Not too long ago I made a post about exhaust coming through my vents. Could a hole (or multiple holes) in the vac lines allow exhaust from the engine bay into the vents?

 

[Adam95GT]

Score.... LOL


Well for exhaust smell coming in... you could have a small leak some where.... Check your headers.... and that hole in the vac line could of sucked in the exhaust...

 

[Rrich]

i found my leak on that vac line right at the connection the other day!!!!

 

[2stangin]

I am brand spankin new, but thank you very much. My ac coming out of the defrost was driving me crazy.

 

[Adam95GT]

I am brand spankin new, but thank you very much. My ac coming out of the defrost was driving me crazy.

welcome to :SNSign::SNSign: