So in the process of performing a boost leak test I came across a weird issue. I set my compressor to output 25psi at the regulator right out of the tank. I then downstream have another regulator and gauge that show 25psi right at where my connection is to the boost leak tester.

When I hook everything up, I am only seeing about 1-5 psi of boost to my aem boost gauge. I know the gauge is not faulty because it acts normal when driving around.

I have a schrader valve adapter that holds the valve open while supplying air. It seems that if I keep cranking the compressor regulator I can get some psi but why are the compressor and motor numbers so far off? I just don't want to put my compressor to 100psi and somehow let my motor get the same.

I am using the STM leak tester.

Am I not accounting for some sort of loss in the motor? Something to do with motor position since some valves are open/closed?

 

A boost leak tester is not designed to test anything but the intake piping, intercooler, ect. If you still have your pressure pipe connected to the engine, you will definitely lose a lot of air pressure. Chances are you have an open intake valve. You may even happen to be in valve overlap, in which case you won't make hardly any pressure at all.
Make sure your hose connection at the throttle body is disconnected and blocked off. then pressurize the piping starting just after the turbocharger. This is to test boost leaks before the engine. If you want to test the engine, then it's time for compression testing and leak-down testing. If you suspect the intake manifold, then a vacuum test at the intake, and maybe a propane gas test is in order.

 

^You can test with the entire induction system connected. You will get some slow pressure bleed off, but the system will pressurize. I've done this multiple times. You start disconnecting and blocking off parts when you need to narrow down small leaks.

Seems to me you have either a huge leak, or you're not getting enough air in fast enough. I always have someone sit in the car and watch the boost gauge to tell me when to stop adding pressure.

 

I understand it does not test the motor. If that valve being open is the case what is the solution? Turn the crank until you find a good spot?

What hose connection at the throttle body are you referencing? I assume if I had that big of a leak it would be audible.

The boost gauge does move up when adding pressure, I just assumed that it would match the regulator right at the inlet.

Can anyone verify their compressor outlet psi compared to boost measured in the car?

 

it takes a while to build up pressure in the piping. When I did my BLT it took about 10 mins to get to 40 psi, but I did have to block of my external waste gate. The volume of the pipes is quite large and it takes a while

 

NO....NO..NO! That is the entire point of doing a boost leak test! Do you drive your car with the t/b blocked off? No. You want to test the car in the same configuration you drive it. So you want to put your tester at the OPENING of the compressor housing inlet. If you have a bleeder type mbc...that is the only thing you should block off since that is its purpose. I personally like using a portable air tank. Those 10 gallon ones that you can fill to 120psi are perfect. Hook up your tester and open the valve and let it pressurize. It should pressurize unless you have a big boost leak somewhere...and bleed off slowly. Doing it this way makes you discover all sorts of leaks. There are many hidden leaks that can go undiscovered using your method eg. Compressor housing leaks, fpr vacuum hose leaks, intake manifold gasket leaks...etc...

 

I am not familiar with the boost equipment the o.p. mentions, but boost leak testing I am familiar with only test the pressure piping and intercooler. Keep in mind too that stock recirc valves do not hold full boost levels, so that is something to consider when conducting the test. You can rotate the engine with a ratchet to help minimize leaks through the cylinder head if you insist on testing the intake manifold at the same time. I'm just not familiar with that process. There are too many variables for boost pressure loss in the intake manifold...yo may chase your tail for what is a normal state. If the intake manifold is leaking boost pressure, it will most likely also leak vacuum. And you can test check valves easily with a hand held manual vacuum/pressure pump.
I'll stop talking an let someone who's doing the test as you are doing it talk you through it!
P.S. Again a leak-down test seems more appropriate for a tb/intake/cylinder head test. It eliminates half of the intake system to help pinpoint problems (like the boost leak test as I described does the other half).

 

I think I can help a bit here. First off, it sounds like you're using two in-line pressure regulators. First, for the sake of safety, turn the PR at the car all the way down. Assuming you are utilizing good air hose between the compressor PR and the one at the car, crank the compressor PR up to about 80 PSIG. That will give your second PR some pressure and flow to work with. Then go ahead and slowly (read: slowly) crank up the car PR to your required boost level, you should hear a lot more flow now with this setup, and your pressure should build at a reasonable speed.

 

Also, with a stock ish setup, you will want to leave everything connected from the turbo inlet all the way to the motor, only disconnecting everything from the turbo inlet back to the air filter. This will leave the DV outlet open to the atmosphere which is exactly what you want to leak check that valve, ie. It should not be bleeding air out of the IC piping in this condition.

 

When looking for my boost leak.. I took off my intake... Hooked boost leak tester up to the turbo and filled it up. I hit 16lbs before I found my leak. You have to build enough pressure for the wastegate to crack open to the rest of the system can charge/fill with air. Sounds like you should do both a boost leak test and a leakdown test.

 

I didn't mean to sound dickish...I was just pointing out the method will work but it's not comprehensive.

 

Hey, we're all friends here! We try to help each other out as best we can. If someone's got it wrong, correction needs to happen or else bad information gets spread. We're cool.
Let us know how your testing is panning out. Maybe we can help more (or better).