I'm under the impression that finding an automotove vacuum leak is a bit of a black art and would appreciate hearing from experienced techs about favored techniques.
I've heard of using a rubber tube or auto stethescope to listen for audible leaks, and some folks have advocated spraying various things around and listening for changes in engine performance/idle speed. Have also read about a smoke test, which I think requires specialized equipment. At the same time, I've read admonishments in manuals, TSB's, etc, that these techniques should NOT be used (solvents/smoke).
Hint: If you had an engine that ran on pepsi, what do you think the engine would do, from idle, when someone sprayed a shot of aerated pepsi onto a vacuum-sucking hose? Similar to what it'd do if he sprayed it into the top of the vacuum-sucking carburetor? How'd you ever come up with that? BE CAREFUL WITH THAT SPRAY BOTTLE OF GASOLINE YOU WERE TALKING ABOUT USING. But, it sure does work good, doesn't it? Glad you thought of it! s
Back when my cars used to have a "vacuum-sucking carburetor" I used to spray this magical stuff called carburetor cleaner into the "vacuum-sucking carburetor" and boy, did it ever affect the engine idle. I don't suppose it would be too much of an intellectual leap to suggest that the introduction of some carb cleaner into a "vacuum-sucking hose" might also affect engine idle speed. Once, I had my fuel injectors cleaned at a shop in town. They introduced the cleaning solution into the vacuum manifold. There was a definite change in idle when they opened the valve allowing the cleaner in. No one has ever suggested using gasoline, however, as you did above. You'll have to let me know how that goes...
"Powell E. Barber" wrote in message news: snipped-for-privacy@nucmar.physics.fsu.edu...
No, actually I went into that spiel because of the opposite--got a spinal disease, and today was an extra good day(they don't come too often). And when I feel good, I tend to talk a lot. Sorry if I offended you: I certainly had not intended any such reaction: my bad: please forgive me; honestly, I really meant to spread the joy I was feeling. Now, to the serious bit. I have been tinkering with cars--made a living for 25 years doing so exclusively--all my life. And anytime I encounter a vacuum leak, I ALWAYS use a spray bottle(Windex or better yet, a generic whitewall cleaner bottle with a strong spray trigger) with gasoline in it. And so far I don't remember it EVER failing to point out where the vac. leak was. I'm sure other liquids might do as well, but I seem to always have some extra gas around, and as long as it isn't broken, I'm not gonna try to fix the analytical 'tool' that has served me so well. I just hope that you may find it to be as effective, and handy, for you as it has been for me. (Should it work as well for you, hopefully you will remember that idiot you tho't was having a bad day.) Good luck to you and I hope this helps you solve your problem. PLUS: I've never even approached causing a fire by using it. I honestly feel since gasoline is running along/around those intake leaks, that the same thing (gas) would logically work as well as anything more elaborate. I've seen others spray starting fluid for diesels (I think it is ether.), but being the mechanical type rather than the chemical engineer, I feel safer sticking with something I'm personally more familiar with. I've also seen carb cleaner used, as you suggested. And wd-40. And rubbing alcohol. And they all work. To be completely honest, the carb cleaner you mentioned probably increased the idle speed more than gas. But I grew up poor(not complaining--it's all relative, and I didn't know it at the time) and probably saw and used real carb cleaner only after I was a teen-ager when I'd already been working on cars/trucks for like 10 years. We used a cheap, clean-up grade of lacquer thinner to clean carbs, starters, generators, hands, etc. Seems like it cost like 85 cents per gallon! And did ok, considering we didn't now what a solvent tank even was! Regards, sdlomi.....PLEASE, again, forgive me!
Instead of gasoline or something equally probable to cause a commotion why not use a fluid that quenches the combustion. I cannot think of anything at the moment but it would be certainly safer. That vacuum leak that you are looking for could be a leaky ignition instead.
Probably not the favoured technique, but on my own vehicles, I first check the vacuum hoses for hardening, cracking at the ends or looseness by gently pulling or twisting on suspect connections with the engine off. If some are questionable, not unlikely they're all hardened and of limited value. On an older carbureted vehicle with rough idle, finally just got a roll of vacuum tubing, labeled everything and replaced them all. Problem solved. Worthy performance and idle improvements. Only wish I'd purchased the better quality vacuum line from the dealer. Now it's years later. Still all fine. But they've all hardened again, and I'm fairly sure if I disturb them, leaks could reappear. Simple answer. If the vacuum lines are hardened and inflexible, just go ahead and replace them. This is not advice for the professional service dept., but what I do.
Use Eyes - Sometimes you can see damaged vacuum hoses
Propane -- Carefully Controlled..
Soap and Water
Soap and water -- Apply to area of interest, look for bubbles.
Propane -- May not work very well on new cars.. Computer and 02 will see the propane and adjust before you know it. On slightly older cars, "deliver" propane to a desired test area with a hose/nozzle. Listen for surge. (Ex. If you happen to notice that when you add propane around the intake manifold, the engine surges -- You probably found it.)
Note on Carb Cleaner: Flammable, I think propane works better.. Less likely to light up on a hot manifold. Use with caution.
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I suppose you would see bubbles on the inside of he vacuum line because it would be drawing air in. But HOW do you see the bubbles inside the hose? We are talking about vacuum are we not?
Basically, we are looking at an air leak. (Vacuum is air at lower than atmospheric pressure) I'm looking for a change/agitation of bubbles.. Air effects soap bubbles.. If a soapy area is being especially agitated or even depleted of bubbles on a vacuum line, I'd look at it.
I tend to use propane to try to find leaks, but if I were propane-less, I usually have some Dawn soap available to wash up with and sometimes it works...
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TIF used to (still does?) manufacture an ultrasonic vacuum leak detector. It "listens" for the ultrasonic noise generated by air leaks. Having used one for about five years, I think it's one of the best detectors available. A bit pricey for a DIYer, though (I think I paid around $150), but is certainly accurate. The only problem I have with it is in Cadillacs with TBI -- the exposed injector ultrasonic noise is so great it easily swamps out small leaks (this thing can detect REALLY small leaks).
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