DIY Boost Leak Tester for SS

After buying a '93 SS w/4EAT sight unseen and replacing the head gaskets, seals, timing belt, etc., it still didn't perform as it should. I was having hesitation upon acceleration, and would experience what would feel like a major misfire under any amount of boost.

Unfortunately it was a combination of many different problems. In fact, I still have a few bugs to work out but my SS is almost back to it's former glory. My advice to anyone that buys an old SS is to replace every single coolant hose, pcv lines, and just about any vacuum line that you can get to. I've had radiator hoses blow, pcv lines crack, most of the air intake break, etc. Some of these parts are very hard to find. I also had to replace a dying fuel pump (DIY here: http://legacygt.com/forums/showthread.php/walbro-255-lph-install-diy-198427.html), the ignition coil, and all four of the fuel injectors. All of this helped but I was still having problems under boost.

With much of the air intake prone to cracking because of age, it is important to find where leaks may be occurring, particularly under boost when the pressure builds up dramatically. You have the option of taking the SS to a tuning shop and have them do a smoke test, or you can build your own boost leak detector. Although it will not emit any smoke, as you build up pressure in the system you can listen for leaks as well as spray soapy water on all the connections and look for bubbles.

I build my boost leak detector from a few parts from the auto parts store and the majority of the parts you can pick up at Home Depot or most hardware stores. I made mine so I could hook it up to a simple bicycle pump although you can also make yours to hook up to an air compressor, but I don't have one. An air compressor would be ideal since I had to have a partner to work the bike pump while I listened and checked for leaks.

Pic of parts and materials needed for detector:

http://i301.photobucket.com/albums/nn41/henry616/Boost%20leak%20detector/DSCF6966_zps4eb2fd83.jpg

Of course your detector doesn't have to look exactly like mine, but it worked for me. Feel free to improve on the design.

List of parts and materials:

Chrome Valve Stem with threads

Valve extender

2"x1/2" PVC Bushing (2)

2" PVC coupling w/threaded holes for nylon barbs (2)

2" PVC coupling with hole for chrome valve stem

Nylon Hose Barb 1/2"x1/2" (2)

Vinyl Tubing 10'

JB Qwik (Not JB Weld)

Hose clamps (optional) (2)

PVC Cement

Bike Pump

Friend to work the pump (optional)

Mix up some JB Quik (you might get away with just using teflon tape) and apply it to the threads of the nylon hose barbs and thread them into the PVC couplings.

http://i301.photobucket.com/albums/nn41/henry616/Boost%20leak%20detector/DSCF6969_zps87e8273b.jpg

Take your threaded chrome valve stem (the kind I found fit perfectly in the 2" pvc coupling) and bolt it on with some JB Quik to ensure a perfect seal.

http://i301.photobucket.com/albums/nn41/henry616/DSCF6975_zps847eee36.jpg

Now cement your valve stem bushing to a coupling, and glue one of the bushings w/barb together. Cement the other bushing to the other coupling which will remain open ended. This open end is what you will attach to your turbo inlet elbow. Attach the hose to the barbs. I needed to use a valve extender on the chrome valve stem so my bike pump could attach to it. I also had to chop the end of the valve extender off because my pump was not able to press the small end of the valve so I opened it up.

Here's what it looks like hooked up to your bike pump all assembled.

http://i301.photobucket.com/albums/nn41/henry616/Boost%20leak%20detector/DSCF7031_zps6fa372a3.jpg

Now at this point some of you are saying why not just make an open ended coupling with just a valve stem with no need for the hose or the additional coupling. The reason I did it this way is my bike pump hose was not long enough to reach from the ground to the turbo inlet elbow.

If you have a compressor, you can just make the open ended fitting with an air compressor hose attachment, which would be a lot simpler than what I did.

All right. We're almost ready to hook it up and start testing! But first we need to remove the air filter intake and resonator, as well as plug the pcv lines and the vacuum lines that attach to the resonator.

The simplest and safest way to remove the air filter and resonator it to first remove the bolts that hold the air intake to the filter and loosen the hose clamps on the elbow that attach it to the resonator. Disconnect the MAP sensor harness and remove the air intake. There is a vacuum line that goes to the auxillary purge control valve, as well as a vacuum line that connects the resonator to the boost control solenoid.

Here is a great vacuum line diagram by VRG that I picked up over on legacy central bbs (http://bbs.legacycentral.org/index.php) which is the greatest site in the world when it comes to information about 1st Gen Legacies. I know next to nothing compared to some of the giants over there, and what little I do know, a lot of it I owe to them. Thanks BBS!

http://i301.photobucket.com/albums/nn41/henry616/vacuumlinesej22t_zps14b06b5a.jpg

Now loosen the hose clamp that connects the resonator to the infamous turbo inlet elbow (16 in the diagram below). Next remove the very large PCV line that attached to the resonator (also very easy to break) and carefully remove the resonator. WARNING!!! The turbo inlet elbow is obsolete and no longer produced by Subaru. It is also extremely brittle and hard to handle. You WILL break it unless you are extremely careful and then you will be somewhat screwed. If you break it you will be forced to find a replacement or fabricate your own. I found this out the hard way when I rebuilt my 22T. Proceed at your own risk.

Here is another very useful diagram (also picked up on legacy central bbs) of the PCV system. Note: It does not show the large PCV hose that connects to the resonator, but that hose is very obvious.

http://i301.photobucket.com/albums/nn41/henry616/PCVsystemej22t_zps703d0d62.jpg

Next disconnect the pcv splitter from the turbo inlet, as well as the PCV nipple (part number 17 in the above diagram).

Now you need to plug up any PVC hose that is open in order to pressurize the system. This will include the large PCV hose that connected to the resonator. I bought some rubber vacuum caps as well as a smaller box of various sizes to accomplish this. I also disconnected the splitter hose from the two PCV hoses and plugged up each hose. Probably not necessary, but that's just how I did it.

http://i301.photobucket.com/albums/nn41/henry616/Boost%20leak%20detector/DSCF7033_zps28605376.jpg

To plug up the large PCV hose that connects to the resonator I had to buy a large heater hose fitting w/90 bend. One end connected to the large hose, and to the other end I connected a piece of heater hose which I plugged with a very large plug and a hose clamp. The large plug I purchased at Home Depot. It is an end cap for their PEX hosing which is normally used in indoor plumbing. There is probably a simpler better way to do this but I was working with what I had. Also I didn't want to risk trying to remove the PVC hose from the engine as it was very cold out and I didn't want to break it as it was stuck fast. I did a few boost leak tests and broke it a few days later anyway.

Next plug up the two PCV nipples on the turbo inlet elbow, and cap the two vacuum lines that connected to the resonator. Take your open end of your leak detector and clamp it to the turbo inlet elbow. It's a pretty snug fit so be careful. The inside diameter of the turbo inlet elbow is 65 mm or something, and the leak detector is about 69 mm. Tighten the hose clamp and everything should look like this:

http://i301.photobucket.com/albums/nn41/henry616/Boost%20leak%20detector/DSCF7027_zps1d4d2f07.jpg

http://i301.photobucket.com/albums/nn41/henry616/Boost%20leak%20detector/DSCF7029_zps938a3bf3.jpg

Get a spray bottle filled with soapy water ready.

Before you start pumping away here are some things to keep in mind. Our T-Leggys are set to run stock @ 8.7 psi. There is no need to pump the system up to 30 psi, although I don't think that I could have done so even if I had wanted to. In fact, my system would not hold pressure for more than a few seconds.

If you are going to use an air compressor, set the regulator to a very low psi, allow it to build up pressure and then turn it off. You don't want to start blowing hoses apart or build up too much pressure in your crankcase. I have heard unsubstantiated rumors of cam seals blowing off under pressure tests. I have also been advised to remove the oil filler cap when doing the pressure test. I didn't do this when I did my leak test but I could hear and see air escaping where the oil filler neck attaches to the block. Again, I had the oil filler cap on.

Under normal circumstances during the operation of the vehicle, the PCV lines will not come under the pressure that you will be subjecting them to during the test. They do not see any boost pressure when you are driving. However, you may hear air escaping from where they connect to the valve cover gaskets. This does not indicate a boost leak at that point.

Get your buddy to start pumping away. Listen for leaks and spray any and all connections with soapy water. Look for bubbles which will indicate a leak. At first I couldn't get any pressure build up whatsoever so I thought that my detector was bunk. After a few minutes of listening I could hear air coming out near the turbo. I sprayed it with soapy water and I found a major leak at the turbo inlet gasket. I checked the bolt that holds the turbo inlet on and it was less than finger tight! I could also detect air escaping from the pcv lines where they attach to the drivers side valve cover. I replaced the gasket a week later when when it finally arrived. It was a bitch to replace BTW. Super tight fit and hard to get at but I didn't want to remove the turbo to make it easier and the TB intake was frozen solid and not budging.

Now I found a leak not on the pressurized side of the turbo, so it wasn't as big of a deal as a leak on the pressurized side would have been. Nevertheless it was a significant improvement in performance when I replaced it.

After replacing the gasket I did the test again and found some very minor leaks at some of the T fittings where the vacuum line connects. A few zip ties took care of those. However, I wouldn't worry about those types of leaks very much. After I zip tied them there was no change in performance or vacuum pressure at idle or pressure under boost.

If you do not have a boost gauge installed at this point I suggest you install one. You will have a much greater idea of what is going on with your SS.

Good luck and happy hunting!

Update: It turns out all my troubles were being caused by a failing MAF!

I replaced it and the SS is now a BEAST! However, I am happy that I did find a few leaks with my tester as well as upgrade the fuel pump, new injectors, new coil pack, etc. since they needed to be done as well.

Now I get to finally enjoy my SS!!!