Vacuum leak
Thread Starter
Instructor
Joined: Jul 2007
Posts: 236
Likes: 0
From: Mobile Alabama
Vacuum leak
My car is a 90 L98 Auto with only muffler elimiators - it seems to lope at idle more than just a little and I was wondering if I might have a small vacuum leak - any ideas on a easy way to find one - so many hoses and possibilities?
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
I have used this technique (which I got from this forum) with success:
- take a piece of tubing 4-5 feet long
- remove the snorkle from the throttle body, and slip one end of the tubing under the throttle plate
- tape up the throttle body with duct tape as best you can trying to make the opening air tight
- have someone who smokes, exhale smoke into the tube
- it will take a couple of minutes for the intake to fill with smoke, and some will head out of the exhaust through the open exhaust valves
- once the intake fills with smoke any vacuum leaks will leak smoke upon exhale
- use a flashlight and have the smoker modulate exhale speed to pinpoint the leak.
- you may have to tape up other points on the engine (PVC, EGR, etc) if they become an issue.
I found a cracked weld in a TPIS intake runner where it mates to the lower manifold on my 86' with this technique.
- take a piece of tubing 4-5 feet long
- remove the snorkle from the throttle body, and slip one end of the tubing under the throttle plate
- tape up the throttle body with duct tape as best you can trying to make the opening air tight
- have someone who smokes, exhale smoke into the tube
- it will take a couple of minutes for the intake to fill with smoke, and some will head out of the exhaust through the open exhaust valves
- once the intake fills with smoke any vacuum leaks will leak smoke upon exhale
- use a flashlight and have the smoker modulate exhale speed to pinpoint the leak.
- you may have to tape up other points on the engine (PVC, EGR, etc) if they become an issue.
I found a cracked weld in a TPIS intake runner where it mates to the lower manifold on my 86' with this technique.
Drifting
Joined: May 2008
Posts: 1,692
Likes: 490
From: Denver, NC
I have used this technique (which I got from this forum) with success:
- take a piece of tubing 4-5 feet long
- remove the snorkle from the throttle body, and slip one end of the tubing under the throttle plate
- tape up the throttle body with duct tape as best you can trying to make the opening air tight
- have someone who smokes, exhale smoke into the tube
- it will take a couple of minutes for the intake to fill with smoke, and some will head out of the exhaust through the open exhaust valves
- once the intake fills with smoke any vacuum leaks will leak smoke upon exhale
- use a flashlight and have the smoker modulate exhale speed to pinpoint the leak.
- you may have to tape up other points on the engine (PVC, EGR, etc) if they become an issue.
I found a cracked weld in a TPIS intake runner where it mates to the lower manifold on my 86' with this technique.
- take a piece of tubing 4-5 feet long
- remove the snorkle from the throttle body, and slip one end of the tubing under the throttle plate
- tape up the throttle body with duct tape as best you can trying to make the opening air tight
- have someone who smokes, exhale smoke into the tube
- it will take a couple of minutes for the intake to fill with smoke, and some will head out of the exhaust through the open exhaust valves
- once the intake fills with smoke any vacuum leaks will leak smoke upon exhale
- use a flashlight and have the smoker modulate exhale speed to pinpoint the leak.
- you may have to tape up other points on the engine (PVC, EGR, etc) if they become an issue.
I found a cracked weld in a TPIS intake runner where it mates to the lower manifold on my 86' with this technique.
When the smoker is exhaling, rev the motor to 7 grand and chop the throttle shut. See if the vacuum sucks his guts out.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
QUOTE=khhammer;1566981724]I use a can of carb cleaner. With the car at idle, spray around any and all hoses and gasket areas. If the idle changes in either direction you have a vacuum leak.[/QUOTE]
This is the easiest, and I believe the best way to check for vacuam leaks...WW
This is the easiest, and I believe the best way to check for vacuam leaks...WW
