Boost Leak Test - How slow should pressure drop?

[Nate355RS]

I can get the pressure up to 20psi no problem but I'm not sure how fast the pressure is suppose to drop.

Starts @ 20 psi
@15psi after 11 sec
@10psi after 45 sec
@0psi after a couple minutes


I've read that pressure leaking out was normal but I'm not sure how fast or slow is acceptable. I know I have some leaks where the TB meets the IM, where an emission nipple goes into the TB, at the adjusting nut on my AFPR, and my BOV constantly lets out air through the whole test.

I'll seal/fix those things as I have time but I'd like to know if my results now are at least decent. What kind of pressure drop do you guys deem acceptable? I know 0 psi would be nice, but realistically what do you want to see before you're happy with a boost leak test.

 

[Archer Fabrications]

I can get the pressure up to 20psi no problem but I'm not sure how fast the pressure is suppose to drop.

Starts @ 20 psi
@15psi after 11 sec
@10psi after 45 sec
@0psi after a couple minutes


I've read that pressure leaking out was normal but I'm not sure how fast or slow is acceptable. I know I have some leaks where the TB meets the IM, where an emission nipple goes into the TB, at the adjusting nut on my AFPR, and my BOV constantly lets out air through the whole test.

I'll seal/fix those things as I have time but I'd like to know if my results now are at least decent. What kind of pressure drop do you guys deem acceptable? I know 0 psi would be nice, but realistically what do you want to see before you're happy with a boost leak test.

I was always told it should bleed down to 0 in no LESS than 30-45 seconds.

 

[ErikTande]

I just installed a FMIC last night, I'll post a video of my boost leak test today after work. I'd love some opinions if I'm ok or not.

 

[Archer Fabrications]

I just installed a FMIC last night, I'll post a video of my boost leak test today after work. I'd love some opinions if I'm ok or not.

What, thread jack?

 

[Nate355RS]

I was always told it should bleed down to 0 in no LESS than 30-45 seconds.

If that's true I should be good. Mine doesn't bleed down to 0 until after about three or four minutes. Once it gets down to 5 psi the needle barely moves.

 

[Nate355RS]

No one else? So I'm good and shouldn't worry about the small leaks

 

[luv2rallye]

You should be good. http://www.dsmtuners.com/forums/art...-boost-leak-test-how-boostpro-net-tester.html

 

[Breezio69]

I would still fix all the small leaks, as they have a potential to get worse in a shorter amount of time.

 

[xuberantz]

Fix the small leaks, it will help a lot. I personally have never been able to get mine to hold boost without slowly leaking down with similar results to what your experiencing...

 

[GSLENK]

I try to log all my BLT's so I can get an accurate idea of whats going on (running SD makes this easy so why not do it)

I started a thread trying many others to do the same in an attempt to get a general idea what a "good boost leak test result" would look like.

So far the best examples are "uuhhh it should leak down very slowly", "It takes me 10 minutes to go from 30psi to 0psi"

So they are all pretty vague.

Here's my rates of leak down using my log, exported to excel, and using a little regression and calculus (MAP reading, followed by rate of PSI drop)
I suspect these numbers are relatively far from ideal, especially since my BLT tester itself leaks around 20psi.


@18 psi, .919 psi/s
@16 psi, .78 psi/s
@14 psi, .63 psi/s
@10 psi, .347 psi/s
@ 5 psi, .141 psi/s
@ 3 psi, .09 psi/s
@ 1 psi, .03 psi/s


If someone is good with airflow calculations, the temperature was about 75*F outside. If not, Ill try my hand at it. See how much airflow is being lost at each boost level and estimate it based on IAT's of 50* to 115* based on ambient air temp.

 

[crimsondragon]

Compressor covers been known to leak a bit as well. Check there. Some turbos have an O-ring installed in place. Most don't so I usually run a small bead around it.

 

[pneumo]

My benchmark BLT leak rate is to see boost drop by 7psi in 15 seconds. I like to start at 20psi for the sake of consistency. So basically, 20 psi to 13 psi in 15 seconds. If it drops slower you're doing really good. If it drops quicker you're loosing some power and it'll spoolup slower.

I don't think it matters how slow it goes from 5 psi to zero since most boost leaks show up at higher pressure. I also like to raise the pressure to 5psi higher than the max boost I plan to run so I can test if a coupler or hose might blow off once I get to that pressure.

 

[Quadsportz]

Do you guys remove the oil fill cap when doing a blt? I always do maybe that's why my pressure drops faster.

 

[miliman13]

http://www.dsmtuners.com/forums/newbie-forum/462901-help-boost-leak-spotting.html



http://www.dsmtuners.com/forums/newbie-forum/460221-did-boost-leak-test.html

 

[Archer Fabrications]

Do those of you running vented catch cans with no pcv plug your valve cover holes so air doesnt escape?

 

[91 GSX]

I actually use my catch can to LET the air escape, relieving pressure. You don't plug the valve cover. You reroute the holes in valve cover to run into catch can,

 

[Archer Fabrications]

But those with vented catch cans won't hold pressure doing a BLT

 

[PieEyedPiper]

Do you guys remove the oil fill cap when doing a blt?

I do.

Long ago, Oldman engrained the notion into my thick skull and now it's habit.
I've seen folks go as far as to pull the breather hoses and pcv hose, too, but really, just pulling the oil fill cap will do the job.

 

[GSLENK]

And why take off the oil cap? To hear leaks under the valve cover? relieve pressure? avoid screwing up the valve cover seal or cracking it?

I have a catch can, and its "vented" when I remove the turbo's air intake to pressurize the system.

 

[pneumo]

But those with vented catch cans won't hold pressure doing a BLT

What? How?
If you have a vented catch can it shouldn't be pressurized by boost. The catch can is just to vent the valvecover/crankcase. If boost is leaking into the valvecover then you need to fix the boost leak.

I've seen people use the cheap parts store PCV valves and none hold boost. Only the genuine Mitsu PCV holds boost and prevents boost from leaking into the valvecover. That's why I like to unscrew the PCV from the valvecover when doing a BLT, so I can see if it holds boost or not.

 

[Archer Fabrications]

I dont have a pcv valve i have the old intake manifold pcv port for my bov and run both valve cover lines into a vented carch can. And it does leak boost.? Unless i loop the valve cover lines.

Maybe you dont understand a vented catch can has no vac to it?

 

[BurrowZ]

Maybe you dont understand a vented catch can has no vac to it?

If you have a vented catch can it shouldn't be pressurized by boost. The catch can is just to vent the valvecover/crankcase.

^This. If you're (excessively) pressurizing your crankcase when doing a boost leak test something is wrong. Either the car isn't fully warmed up or you've got other issues.

 

[Archer Fabrications]

Interesting cause i have perfrct compression too. Maybe it was leaking from the holset drain i to the crank case.

None the less i dont have anything wrong, it's just weird . I pressureize the compressor cover of the holset when it was off the car and it seeps boost a little into the drain?