pressure testing for boost leaks
 

Ok, i think i have a boost leak and heard you can block off the inlet to the 2nd turbo and use a cap with nipple to pressurize the inlet to the primary turbo. I did this and got zero pressure build up. So after swearing, i figured i would try and pressurize just before the IC through the intake system and zero pressure holding their either. Outside of the obvious that i have huge fricking leak what else could it be? can it leak around the rotors and out the exhaust?

So has anyone actually done this and have any tips?

i was also thinking i could cap off at the Y pipe coupler, and both turbo inlets and pressurize it to test that part of the system (turbos and gasket to the block).

What are you pressurizing with?

From what I understand you need a very high volume air source to find boost leaks this way, and you would want to test the section starting at the y-pipe and running all the way to the throttle body. If you include the turbo itself you'll a lot of leaks since there are multiple nipples and hoses that would need to be capped.

Dave

i got an compressor in my garage, so i am using that to inject air, and hten i have 1 way valve and a gauge. but it won't hold squat, instantly leaks out no pressure what so ever in the throttle body.

why do you need a large volume of air? i thought it would take a bit to get the pressure up but then where would it go if i don't have a leak? clearly the intake goes in to the compbustion chamber, i was assuming you don't have a straight path from the intake to the exhaust correct?

Try looking to the bottom of this page:

http://www.fighters-garage.com/rx7.html

They only using 4 psi.

They fail to tell you that you have to turn the motor to a position were the seals are not just allowing air to pass through and out the exhaust! Lowes has the parts to make these all the way to 6'' turbo inlet size. Use tire valve that has a thread and nut and use pvc cap of the right size and rubber coupler.

Ok, so how do you know where to position the motor so it doen't leak. I have all the seals as you describe. so it most be the motor position?

I am still testing the inlet, but thought of testing the turbos, but someone said i had to plug stuff off, i thought all the release pressure solinoids are closed when the car is off.

I dont know about the stock set up as i have never owned a stock rx7, but have someone listen at the exhaust and rotate till it seals and starts building pressure. You can also have soapey water solution in a water bottle to help find leaks! I find it hard to find leaks a 4 psi. Good luck let us know how works for you.

crap, more trial and error, why only 4 psi? it needs to hold more, but i guess at this point i am just pissed.

Well maybe they meant that at only 4 psi they found their leak.

Ok, so does anybody know for sure....

it air will directly leak to the exhaust from the intake (based on position)

if so, how do know where to turn the motor, and how do you see it, these don't really have TDC do they..

anyone?

Understand that both rotors have to have the intake pathway to the exhaust sealed off and this is not going to happen (I think). If you put the front rotor in the position where the intake opening is just closed, the other rotor is opened and vice versa making it impossible to seal both at the same time. The only way that I think you could do this would be to remove the UIM and install a "fake gasket" with only two of the holes opened. Torque this down and rotate the engine to the correct position. This will then determine if that pathway is sealed. Now also remember that there are vacuum lines tied to the intake that will also allow air to bleed off. They either need plugged with nipples or the lines pinched off somehow. Also, you will have a certain amount of bypass air going around the side seals and the apex seals as they will most certainly not seal 100% tight.

I think the original intention of this was to plug the elbow coming from the intercooler to the intake pipe, plug the intake to the front turbo, and install the plug and gage to the intake to the rear turbo. Pressurizing this will then tell if the Y Pipe or components between the air filter to the intake charge has a leak. Usually the leak ends up being one of the intake flex pipes, Y-Pipe, or blow off lines.

Tim


Tim

well i thought the if the intake port was open then the apex seal would close off the exhaust. i still would think that even in that scenario it would at least leak slowly. in my case as fast as i can put in 5lbs it is gone. I can hear some air around the intake UIM/LIM but can tell if it is going through the IM or something leaking. since i have sequentials i have the rats nest and can't see anything really.

but supposing the apex seals worked or i plugged the exhaust and solved that issue, where would air bleed off, i.e what vacuum lines would i need to plug.

This is a pic from fighters-garage.
http://img.photobucket.com/albums/v4...fd-tester1.jpg

So you're supposed to plug one side of the turbo inlet and have the gauge/coupler on the other. I'm thinking that if you plug the exhaust at the cat-back or maybe the downpipe, then you'd be testing for a leak anywhere from the intake to out the exhaust.

I just sent them an email asking the proper way to use this and sent a link to this thread. They are closed tomorrow, so the soonest I'll get a reply is probably Monday.

appreciate it Aharada...

here is where i am at. i did exactly what was shown in the fighters garage. plugged front turbo inlet and pressurized the rear turbo.

Built zero pressure.

so i figured i would pressurzie for the IC --> engine via the intake system

Built Zero pressure

bypassed the IC and now have a pressure cap in the elbow it builds zero pressure, leaking as fast as i can put it in.

So.... i am here with trying to understand the following: can you really pressurize from the intake elbow? or does it just bleed out of vacuum lines or by the apex seals and out the exhaust? This is what is critical that a) you can do it and i have a massive fricking leak, or you can't do it and my car may not have a leak at all.

I pressure test my charge system right after the turbo, but I have a single upgrade so I don't know if that makes any differance.. I just keep on pumping air and turn the motor until it holds pressure, you could hear air coming out if the motor is not fully close..

Hey all -

Being a Fighters flunkie, I figured I'd chime in with a little help. Jimmy at Fighters told me about the questions when I was at the shop today (putting in a Koyo radiator on an FD, BTW :)) so here I is.

I don't know where the 4psi figure is coming from - I usually pressure test to around 10-15 psi. If you go crazy with air pressure, you just end up blowing hoses and couplers off that aren't designed to hold a ton of pressure.

Yes, you will get some leakage through the motor and into the exhaust system. I've heard of some people blocking the exhaust off (like rubber banding a thick plastic bag over the exhaust tip (don't do with it hot!)) but that's a little overkill.

Basically, I use the gauge to make sure I'm not building up a crazy amount of pressure. Pressurize it to 10-15 psi, then look, listen, and feel for air leaks. Using this method, I've found quite a few leaks, even pinhole leaks in IC piping welds. You have to use a little time and patience, but it's well worth it. On my old FC, I found some surprising ones, like crappy auto parts store vacuum caps that were leaking - the top had split, and would "flap" open when you applied pressure.

Hands down, though, the best remedy for boost leaks is just discipline. Use good silicone couplers and hose clamps tightened up properly, make sure air flanges are flat and true with a good gasket, etc. Put everything together right and you don't have leaks.

Anyhow, the Fighters tester makes finding boost leaks much easier, but it isn't foolproof - you have to do your own look, listen, and feel, and maybe pull a part or two off to see where the leaks are. Any leaks up to the throttle body will cause a loss of boost pressure and power, and post-throttle body leaks will make the car run poorly, since the MAP sensor expects no leaks with a solid signal after the throttle body. Yeah, you can make a similar tool from hardware store parts, but the Fighters tool is well made and does the job great. BTW, Fighters has boost testers in many sizes, so if you need one for a single turbo he can make that too - I think he's even made a 4" one or something for a single turbo Supra.

Hope this helps some!

Dale

Thanks for the quick reply DaleClark! Great information.

Dale, thanks for the info.

ill try to rotate the engine to see if i can get some pressure, because i am getting zero. the IC piping is fine, very expensive couples and yes i checked them all. So either it is in the LIM, UIM, TB or some other thing like the ACV or one of the miles of damn vacuum lines.

i can hear it but not sure if it just the sound of it in the UIM or not yet, guess i got some MORE time in the garage. I have tons of patience and took all the crap off a couple of months ago to change out the primary fuel rail seals and checked everything and it all looked good. So i am really chasing a demon or i got a craked apex seal.

i guess it doesnt matter which way i turn the engine does it, i am using a torgue bar on the crank nut, and it turns very easy.

If you're unsure about your motor, do a compression test. It's easy, takes 10-15 minutes, and gives you immediate answers.

Dale

Dale, thanks. two questions.

First how many rotations do crank take to rotate the rotor one cycle. i rotated it about 180 degrees and saw no increase in my pressure retention. Kids prevented me from getting back to it yet.

Don't you need special equipment to do the compression test? beside a standard compresssion guage?

Ok, got a second confirmation that the rotors do have to be in the right position. i asked this source the same time i wrote the thread, so as Dale always tends to be right, just wanted to confirm it.

Just need to get off the business trip and see if i can get some boost to build up. or i am off to the hardware store to buy some sheet aluminium so i can section my test more precisely.

Ok, need some help. i just rotated the crank 360 degress and the intake will not pressure and i know some of the air is going out the exhaust. Does that mean i have a seal going in the motor?

So i guess i need to think about a compression test?

Does your car run? Can you build boost at all? Seems like you might be overlooking something.

If it were me I would focus on one thing at a time. I would first do a compression test to make sure the motor is healthy. Why spend time on a blown motor.

Next I would try to find the boost leak. I would open up the exhaust at the most convientent spot and use that gasket as a template to cut out a block off plate that close that up effectively turning the entire engine into an air tank. Block off the primary, pressurize the secondary and start looking for leaks. If it's not holding pressure than I would put a little soapy water on all the couplers and such and look for bubbles.

If you can eliminate all the couplers and everything to the TB than I would consider pressurizing from the TB on and look for leaks on the manifolds.

Are you sure all the vac lines and such are on tight and in good shape?

In an attempt to clarify this whole 4psi thing.... I read it as "We started to pressurize the system. A stock system will make 10psi of boost, so we were going to pressurize to 10 psi. we started @ 0 and when we got to 4psi, we found our first leak. We corrected the leak we found at 4 psi and continured pressurizing to 10psi'

That's how I read the fighters comment. Personally I would pressurize the system to whatever your boost is going to be. Something may bulge and leak @ 15psi but not @ 4psi.