Thread: How to check for intake leaks?

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Hi,can you guys tell me how to use a vacuum gauge to check for intake manifold vacuum leaks?Thanks.

Originally posted by techinspector1
Never thought much about it, don't see how you could. But it did get my mind going. What about this? I'll assume the use of a carb, although with some ingenuity, you could do the same thing on an efi motor. Remove the carb and make a flat cover plate from maybe 1/4" steel to replace the carb and block off the hole in the intake (with gaskets to make a leak-proof cover). Remove the valve covers and all spark plugs. Procure a fitting that will screw into the spark plug hole in the heads and allow a rubber hose to be fitted over the nipple end of the fitting. Roll the motor over by hand until any cylinder you want to start at has the intake valve open to full lift (doesn't need to be exact). Now, pull another running vehicle up next to the car to be checked. Plug your vacuum gauge into a manifold connection on the running car to record the vacuum at idle. Now run a line from the manifold of the running car to the manifold of the car to be checked. Connect your vacuum gauge to the manifold to be checked. Record the reading. If the motor being checked is pulling the same vacuum as the running vehicle, I'd say the checked engine is sealed up pretty well on that set of runners. On a 180 degree manifold, you'll be seeing vacuum on 4 of the runners at the same time. You can tell by looking at the runner layout. If you see reduced vacuum, use a stethoscope to listen for the hissing sound of air moving from outside of the manifold or from the valley of the motor into the manifold runner from inside the motor. Now move your nipple to one of the cylinders on the other quadrant of manifold runners and repeat the procedure. The further away your running vehicle is, the easier it will be to hear air moving around in the checked motor.

Does this make any sense to anybody out there?????...or am I way off in left field?????

you're way way off in left field. some people make a living finding vac leaks. there are better ways than that, but ill watch him do what you just suggested and see how it works. go for it aftershock2222 .

Originally posted by techinspector1
After I've had a while to think about this, I think you'd be hearing air being pulled past the rings too, maybe????

It might be better to have both valves closed and drill and tap the block-off plate for the nipple.

"there are better ways than that"
Don't leave me hangin' Mike, please explain.

you might be on to something keep going.

you guys are doing it the hard way. all you have to do is take a little Benz propane torch and turn it on witout flame. start your motor and follow around the intake with the popane and your engine will run faster and smoother if you find a leak. if it has a miss due to a vacuum leak the miss will usually go away when the propane hits the port with the leak. WD-40 works for this to but it makes a slippery mess.

Originally posted by 53 Chevy5
you guys are doing it the hard way. all you have to do is take a little Benz propane torch and turn it on witout flame. start your motor and follow around the intake with the popane and your engine will run faster and smoother if you find a leak. if it has a miss due to a vacuum leak the miss will usually go away when the propane hits the port with the leak. WD-40 works for this to but it makes a slippery mess.

53 Chevy5 i know that tell tech.

Originally posted by techinspector1
After I've had a while to think about this, I think you'd be hearing air being pulled past the rings too, maybe????

It might be better to have both valves closed and drill and tap the block-off plate for the nipple.

"there are better ways than that"
Don't leave me hangin' Mike, please explain.

ill get you out of this mess youve gotten into tech. what would you do without me. the only way that will work is you have to put about 15 lbs of air in the plug hole, then get out your dish soap and water bottle, and spray the intake, get it all soaped-up and then watch for the bubbles. the secret to this whole thing is "THE BUBBLES". that will be a good name for it "the tech bubble check".

Originally posted by techinspector1
Thanks Mike. I always try to respond in the simplest, cheapest way and assuming that the guy asking the question is working out of a 1-car garage with just basic hand tools and no shop air. I have an idea that the majority of those asking fit into that description. If they had all the tools of the trade, they wouldn't be asking nutcases like us.

thats for sure.

Thats much better! Its Sunday somewhere. Be N I C E.

Yikes, Tech! Are you, by any chance, an Engineer for GE??

Just for clarification: GE made (makes?) some of the best, but most over-engineered high voltage switching equipment that I ever worked on. They had multi-stage compressors flowing through dual regulators then through a secondary regulator, all controlled by redundant electrical controls. They worked beautifully when they worked right, but trying to troubleshoot the things was a real puzzler.