TheHunt

88 SE

I've been working on my car by myself for a few years now, fixing every problem and never taking it to a mechanic. I've basically been teaching myself.

One thing I don't know how to do is checking for vacuum leaks.

I need to know EVERYTHING about this. From what to use, where to use it, and what to check for. Even where the vacuum lines are (I know, I really am a n00b at this stuff).

If there is a guide out there, that would be awsome.

I thank you very much for all your help.

ilike2eatricers

I dont know of any guide but just get some carb cleaner and spray it over vac lines while idling. It the engine stumbles that is when you found your leak. You can also do this with a garden hose with a small stream of water instead of carb cleaner. I have never had to check for vac leaks yet though.

TheHunt

^^^

ERAUMAZDA

use a scope to hear any sounds of a leak.

It only works for some people...but the doctors ears can hear everything.

fastrotaries

a soapy solution, and a few cotton swabs. My preferred method is starting fluid that is high in Ether, if even a little gets into your intake your RPM'S will raise and you will know.

ERAUMAZDA

detergent is not health for an engine......I think you are talking about boost

Boost Lee

iTrader: (3)

Here are the thoughts behind it.

At idle you want your mixture to be just perfect so that the second you introduce anymore air (throttle body control) the ecu detects it and adds fuel and the rpms increase.

I think typically what happens is a vacuum line cracks. In this case you get more air than you need and since the air flow meter is measuring all the air that comes in, by the time the injetors fire, some air will have leaked in through the vacuum line because of the vacuum produced by the engine running and now your mixture is lean (more air than the 14 to 1 ratio with fuel called stoichiometric or 'stoich'). When you spray carb cleaner or any of those combustable liquids around your vacuum lines, you are temporarily evening out the mixture. Since there is more air than idle requires and more 'fuel' than idle requires the engine rpms will go up when you spray that stuff in the right spot.

Now another scenario is when you have too much fuel. The engine will probably respond slow off of idle. All you have to do in this case is pop open any of the vacuum lines. You'll need to cap the line and the nipple you pull it off (your thumbs will do). Take whichever one you sense a vacuum from and follow the rest of the instructions. If you allow just a little more air to enter the engine and the rpms drop, you've got a pretty good mixture. Alternatively, if the rpms rise, you've got a rich mixture and I have no clue how to fix a rich idle with fuel injection so I'm going to shut up. But at least you know how to detect that situation now.

JGard18

yeah, carb cleaner.

if the engine starts racing at one point of spraying, you've found your leak.

Driv300mph

I was told to use fuel injector/throttle body cleaner instead of Carb cleaner, being that we don't have Carburetors!!!

Henrik

Buy a small propane torch and 6-10' of hose. Unscrew the "flare" piece of the torch and put the hose over the remaining valve. Start engine, open the valve and start probing around fittings, flanges, diaphrams etc with the hose. If you hear the idle change you've found a leak. To get an idea of what your looking for, start by "probing" the intake, this will show you how the engine responds. You may have to adjust the idle mixture down to make it more noticable (turn the R/L adjust towards L (lean) - don't forget to remember where it was so you can put it back after searching). Propane works well as it doesn't leave any residue and is cheap (many shops use propane for finding vac leaks). With the hose you also be very selective about where your searching for the leak.

Forgot one thing - the hole in the torch is really small, you may need to drill it out a bit to get enough flow - you just want to enlarge it slightly otherwise you'll drain the bottle in minutes.

You can also use the hose to listen for leaks - stick one end in your ear and probe around with the other. Listen for hissing.

I've found vac leaks both ways.

Henrik

ilike2eatricers

Not to knock the propane idea but that sounds very dangerous especially since the motor is running as something could spark the propane. That wouldnt be pretty. Isnt it possible for a spark plug wire to be somewhat loose and sparks fly out? I think there was someone who posted that earlier today.

Driv300mph

yeah... WAY too dangerous for me to ever try

c-squared

Same stuff, different packaging (for the most part), Carb cleaner just leaves a little extra residue for lubrication.

I prefer to hook this method: get a mechanic's stethiscope and a vacuum pump, either power or manual.

Seal the opening for the intake at the front of the afm. Saran wrap over the front will do fine, just make sure it seals.

Disconnect the vacuum hose from the pressure sensor. Develop vacuum through the hose, then listen for leaks.

I find this way works best since you can do it with the engine off. You may have to alter the crank position in order to develop vacuum via the 19mm bolt on the front of the pulley.

ilike2eatricers

Is there a difference between a mechanics stethiscope and a doctors stethiscope?

c-squared

Mechanics stethiscope can fit an air horn to listen for hisses alot easier, as well as a contact needle so you can pinpoint clicks or banging sounds (such as hearing your injectors cycle when the engine is running)

With the air horn, you don't need contact with the engine parts, which a medical stethiscope requires.

The automotive stethiscopes are around $10 to buy.

Henrik

OK if your going to check for vac leaks at arcing plug wires then your going to get the same result (fire) with propane or carb cleaner (which is also very flammable)

Use what your comfortable with.

Henrik