DIY: Exhaust Leak and Boost Leak Tester (simple, no glue)
Exhaust leaks are often troublesome to locate if they don’t leave the tell-tale black soot around the suspect area.
I could not for the life of me locate this leak and it was driving me crazy. I knew there was a leak because I could smell rotten eggs after some spirited driving and the cabin would stink after a long drive. It seems like the fumes were getting pulled through the vents in the trunk and making their way into the cabin. After much frustration, trying to plug the pipes with the engine running, etc. it was just too loud and there was too much air moving for me to feel or hear the leak. So, I found a cheap way to pressurize the exhaust with a few things from your local hardware store. I hope it helps someone that is having the same problem I was.
I’ll start off by showing you what I’ve been using for a boost leak tester; you can skip to the bottom if you just want to see how I used it to check the exhaust.
Boost leak tester:
Materials:
-2” PVC Cleanout adapter with threaded plug:
-Tire stem:
-Locking Air Chuck:
-Wine Cork
1.) First take the threaded plug out of the cleanout adapter and drill a hole from the inside of the cap. The size of the hole will depend on the size of the tire stem that you find(or if you use a quick connect airline fitting), but you want to make the hole slightly smaller than the recessed part of the tire stem.
2.) Insert the tire stem from the inside of the cap, and then thread the cap back onto the cleanout adapter:
3.) Take a razor knife and cut the nubs off of the cleanout adapter so it will have a good seal around the TIP:
I feel that this is a very simple, cost-effective boost leak tester and I’ve used it for a while now. Along with a spray bottle full of soapy water, this is an indispensable piece in my toolbox.
When testing for leaks, don’t forget to take the PCV line out of the TIP and plug it with the wine cork and a hose clamp. I usually don’t exceed 5psi.
Compressed Air:
Living in an apartment has been very tough for the last few years, and I can understand not having an air compressor due to space (or spousal) restrictions. Here’s what I use instead of a compressor:
It’s a 7gal Blackjack air tank from Wal-Mart with the hose removed and replaced with a ball valve, a cheap POS air regulator from AutoZone, and an air hose that was out of a kit of air compressor accessories from Lowe’s. I won’t go into much detail unless someone really wants me to, but it was fairly cheap, and I can just fill it up with a gas station air compressor, or I can fill it through the hose at work. It also fits nicely in a closet and is portable. I can get more than enough air from it to do multiple leak tests.
Exhaust Leak Tester:
Materials:
-(1) 1.5” to 2” Rubber Fernco Coupling
-(1) Toilet Tank Repair Ball (Fluidmaster#80813)(toilet parts aisle)
-Your existing boost leak tester
-Compressed air with some type of regulation
I mounted the boost leak tester in the Fernco reducer coupling, which fits quite nicely in the stock sized tailpipe:
Use the toilet ball as a plug for the other pipe:
It took about .5 seconds and very little pressure for me to determine that my flex pipe was toast. I had tried 5 or 6 times to get under the car while it was running, but it seems that it was only leaking when the motor was under load, so no matter how many times I would have looked, I never would have definitively narrowed this down as the leak without pressurizing the exhaust.
I hope this helps someone out.
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Noggy S4 Avant MT B6 
Originally Posted by dubgli
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