Vacuum leak testing

[Tempest]

As stated I'm trying to track down a vacuum leak.

I've sprayed about 3 cans of carb cleaner on every gasket and line that I can find to no avail.

I've read that you can either put about 5psi of compressed air into the motor via the dipstick tube using soapy water as a detector OR pull a vacuum with a pump and see how long it takes leak down. Closing up the air inlet first and with the engine off for both operations of course.

Is this correct?
Thanks.

 

[ksJoe]

This may be a dumb question, but if you can't find it, how do you know you have a leak?

 

[demarpaint]

Carb cleaner has always worked for me.

 

[Tempest]

https://bobistheoilguy.com/forums/threads/p0171-p0174.100017/

 

[ksJoe]

You could try gently squeezing the vacuum lines with pliers to close them off. Listen for the idle to change.

If you have a vacuum operated cruise control, it may be leaking internally.

 

[Tempest]

Thanks.

No cruise control on the truck.

 

[demarpaint]

Did you check the EGR valve for vacuum leaks? I had one drive me nuts! The mechanic swore up and down he couldn't find any vacuum leak, and claimed he tested everything. I ended up finding it with carb cleaner, what a tough one to find.

Frank d

 

[Turk]

Put a vacuum gauge in-line and pinch/wiggle each line and fitting, so when the gauge flinches, you found the leak!

 

[Tempest]

I'll have to take a specific look at the EGR tonight. Been researching that as well. Thanks for the tip.

 

[Gary Allan]

See if any of the shops near you has an ultrasonic leak detector. Mine got stolen at work, but I could find a pump seal leak in a room of 35 running pumps (and something like 150db+ background noise level) merely by pointing the microphone and reindexing the sensitivity. Some windshield outfits used them for finding leaks.

I assume that you've unhooked the umbilical to the cab and plugged it to isolate the engine bay??? Air doors actuators can be a source of the leakage.

 

[saaber1]

Here's an interesting method. Anything involving a dog food can has to be good!

http://forums.vwvortex.com/zerothread?id=2692757

 

[Steve S]

Did you check the brake booster?

 

[Chris142]

With a leak that big I would think that you could hear it.

 

[tom slick]

I'd look at any vacuum actuated stuff like the vacuum advance, transmission modulator, EGR valve, etc. After the first can of carb cleaner I'd have given up on finding the type of leak carb cleaner finds.

 

[moribundman]

Originally Posted By: Chris142
With a leak that big I would think that you could hear it.


Unless he suffers from bad hearing.

 

[mechtech2]

Why not try and find the gas tank leak?
Because maybe there is none!
If the carb cleaner trick doesn't help, use the old time consuming method of tracing each hose, and it's ends.
Buy like mentioned, you brake booster may be leaking, or a heater door valve in the interrior. Also the EVAP system.

 

[CharBaby]

I've used a hand held propane torch to find leaks, just don't light it. Hook up a long hose to the end of the torch, open the valve and move the hose around the engine compartment while the engine is running. If you notice a change in idle, you have found your leak.

 

[Smoky14]

When I had my shop I had a smoke generator which made finding leaks a lot easier.
Find a shop that has one and it will save time and money.
Just a thought
Smoky

 

[George7941]

Just one tip on leak testing with carb cleaner or propane.

Sometimes the change in rpm is too small to hear. For example, if the idle speed went from 700rpm to 710 rpm, you minght not hear the change in speed. If you hook up an instrument that has a digital readout of rpm (I use my Innova digital advance timing light), you will see the 10 rpm increase on the digital readout.

I once found a intake manifold leak on a Ford 4.9l engine using propane. The change in rpm was so slight that I could not hear it but it showed up on the display.

 

[Colt45ws]

Another thing is it has electronic idle control, so it will try to keep it within a set range.