As noted in my recent post I've got the UIM off and am starting at the LIM looking for vacuum leaks. And if you saw my compression test video it appears I have consistent pulses at 105psi on both rotors.

I used rubber stoppers from HomeDepot to plug the LIM ports and put nails in the vacuum lines to plug them. Here's what it looks like:


<a href="http://s366.photobucket.com/albums/oo104/vrracing/?action=view&current=photo.jpg" target="_blank"><img src="http://i366.photobucket.com/albums/oo104/vrracing/photo.jpg" border="0" alt="LIM Pressure Test"></a>


I have a gauge on the brake boost and am pumping air from my compressor into the tube feeding the primary intake at around 15psi if you believe the gauge on the compressor's regulator.

When I apply the pressure, I can hear a bit of hissing around the primary injectors but cant localize it (might have to pick up smoking! ). However, I can also see the oil in the OMP/MOP lines (I rebuilt them with new clear tube per a writeup I found I think in the archives) moving back down toward the OMP/MOP. They hadn't completely filled with oil yet as I haven't run it enough for that yet. And some of them are still pretty empty.

Also, when I stop applying pressure, the gauge immediately drops to zero. Is the expectation that it should hold pressure?

Thoughts?

 

So no one else has really done the pressure test?

 

I've done this very thing before looking for leaks on my 3rd Gen. Could never build any pressure at all, was even able to use "lung power" w/o any resistance....

I had leaks (hissing sound and could actuall feel the air leaking) around my secondaries when I used compressor.

I'd like to know too if the LIM should hold pressure like this?

 

it should hold a certain amount of pressure, yes.

 

How much pressure and after I release the pressure how long should the manifold hold it before dropping to zero, Cygnus?

Thanks

 

I am bringing this thread back. I was wondering the same question, how much pressure and for how long should the intake hold? Also when you have fixed all leaks will you still be able to hear air running though the intake. I thought it was still hissing after replacing a bunch of suspected bad vac lines, but I don't know if it was just the sound of air going through the manifold.

 

You shouldn't need a lot of pressure to test for vacuum leaks. Just use a mixture of dishwash soap and water and a spray bottle or mister and look for bubbles while adding the compressed air. LIM gaskets and injector o-rings are common leak areas.

 

I have pressure tested extensively, both by pressurizing the turbo inlet and by pressuring from my Greddy TB elbow with the engine on an engine stand.

You are not pressurizing the system and then just leaving it there to see how long it takes to leak out, it's not that kind of test. The air is going to escape through the exhaust ports. You are pressure testing to feel, hear, and see (bubbles from spraying soapy water) air escaping.

What you want to do is hook up your pressure tester and gradually increase pressure on the air compressor regulator from zero. Don't worry how much pressure the regulator says you are pushing. Look at your boost gauge. If you have a lot of leaks your boost gauge may never go over 0-1psi. When I had my car leak free on my old motor, I could crank the air compressor up until my boost gauge read about 15psi, and then the tester would shoot out of the intake (loud boom sound) as the worm gear clamp couldn't hold it in place anymore.

Yes, but it is a much more muffled sound than when you are actually leaking. If you don't feel air escaping and spraying soapy water results in no bubbles, I'd say you are fine.

 

I just did that test on mine. UIM removed. I found out my fuel injectors were leaking bad. Took them out and there are no grommets! Just ordered new one from Mazdatrix.

Guess that explains the crappy idle.

 

Thanks very much for the explanation. My idle is good and I pull 13.9-14+ inHg at idle according to my Rtek. I was also wondering if anyone had a inHg for idle that is standard. I had read some varying numbers.

 

depends on porting, idle rpm, health of the engine, etc. 14 inHg is on the low side for stock ports though. With no vacuum leaks and a big streetport I was pulling about 15 inHg on my s4 T2, that was on the old motor though.