Finding Vaccum Leaks By Pressurizing

[courier33]

I have read heaps of threads about rough idle, stalling etc etc and it seems to come up very often that intake leaks are the source of the problems.

Its pretty hard to find a small leak when the car is running by listening for it, especially with the noisy engine fan, and it can get messy with a can of wd40 or something similar being sprayed on every seal and clamp.

So I have been thinking about another way of checking for leaks.

Has anyone considered making a blank that fits inside the rubber hose on the intake pipe where it bolts onto the throttle body, and another blank that fits over the air flow meter where the fliter attaches. Then fit a rubber tyre valve stem into one of them and pressurizing the intake system to say 20 psi.

It would be a lot easier to listen for leaks this way when the engine is off. Also I was thinking you could not have a blank on the throttle body pipe, but instead put one on the dump pipe/exhaust tip and pressurize the whole intake/exhaust.

Can anyone see a problem with this? Im thinking of making some blanks up to check my engine but dont want to damage anything in doing so.

[Bass Junky]

Fill it with water and pressurize.

[GTR1993]

No problem, in fact i have seen kits for sale on the internet for this very purpose. I think it would work well.

I wouldnt go where the air flow meters are, i would go just after the turbos. Turbos them selves wouldn't be 100% sealed around the shaft.

Edited November 13, 2007 by GTR1993

[RBwhatever]

Already been done before. Here's the general instructions.

You can do a leak test.

What you'll have to do is,

1. take your pod and AFM off.

2. use a baked bean can (full) and put it into your rubber intake pipe (assuming its still the stock one).

3. tighten up the hose clamp onto the tin creating a seal.

4. Open the throttle body with a brick on the accelerator pedal, so you can read pressure on the boost gauge.

5. take a hose that is plumbed into your intake between the turbo and the plenum or off the plenum itself.

6. Get an air compressor and pressurize the system through the hose and get someone to read the psi on the boost gauge. you only need about 5psi. you can use the compressors at the servos.

7. Listen for a leak. And use the soapy water in the spray bottle to find exactly where it is if need be.

It is easier to find a boost or pressure leak using this method because the car is not running and is easier to hear and locate.

[justin911]

i used a 2L coke bottle... no need for the hose clamp

when u take it off it makes a reealy loud pop so seemd pretty airtight

[courier33]

Thanks for the feedback guys, it certainly seems a better way than trying to listen for a leak when the engine is running. Not surprised its been done before tho.

Funny to hear the different ways people use to plug the intake up. Maybe jam a spud in there, it works well up the exhaust

[RBwhatever]

4. Open the throttle body with a brick on the accelerator pedal, so you can read pressure on the boost gauge.

I forgot to add, this is if you've got a mechanical boost gauge installed. But it will pressurize your plenum to check for leaks on it also.

[courier33]

Interesting you say this about pressurizing the plenum. This must mean that rb cams have 0 overlap. ie only intake or exhaust open at any time? Therefore pressurizing cylinders without losing pressure through exhaust ports is possible?

[RBwhatever]

I did it on mine. My boost gauge is taking its signal from the plenum so I can only conclude its pressurizing it.

But i have heard of pressure being lost out of the exhaust which means they will have overlap.....I think.....enlighten me.

[Haines]

would you need to wait till engine is cold for this

could the air be too cold for a hot engine (if there is such a thing )

Edited November 13, 2007 by Haines

[RBwhatever]

would you need to wait till engine is cold for this

could the air be too cold for a hot engine (if there is suck a thing )

No. Simply put rhetorical Q's, what are intercoolers for? and C02 kits, and ice boxes, and cold air intakes?

[Haines]

yeah thought as much

but just thought id check before giving the engine a blast

[courier33]

The rb25 plenum can be pressurized without the air leaking through the exhaust valves. I just tried it and the first time there was a leak, but i cranked it over a little bit and it sealed up. Removed afm, blocked the intake pipe, and pumped it up to 5psi through the fuel pressure reg hose that goes onto the manifold.

[RBwhatever]

Nice. Good to see it worked

[Haines]

did mine too

Leaky BOV Mount

[FineLine]

Did mine after some recent tuning issues and found a few small leaks. Got a piece of pipe and welded a hat onto it in to whichwe welded an air hose fitting and clamped it on behind the afm. Worked a treat and helped us solve a couple of niggle issues that has plagued us for a while.

I wouldnt do another build without doing this before it went to the dyno.