How about a Tech Thursday (TT). I'll pick a technical topic related to our cars and elaborate on it. Then we can discuss ask questions on the topic. Sounds good to anyone? I hope so!
Today I will discuss boost/vacuum leaks and how to perform leak detection to find and seal leaks.
As we all know, our cars have a very complex vacuum system on top of a long charge piping system with many joints to fail. That's the joy of owning a German car, they love to over-engineer things that are universally simplified on other cars. The age of the cars and the heat that hoses are constantly subjected to doesn't help the situation as well. We've all had split hoses spring up on us at some point or another... and they can be a pain to find.
First line of defense is good clamps. T-bolt clamps or Mikalor clamps for you guys in the UK is a good way to improve the clamping at the joints and prevent leaks to develop there. These type of clamps spread the load evenly and hold their clamping for a much longer period of time than the conventional worm clamps (jubilee I believe they're called on the other side of the pond).
Second thing that help is to progressively service/replace the hoses in the vacuum system with higher grade reinforced silicone based hoses. PVC system is the biggest offender there and always a good place to start refreshing the vacuum system. Other usual suspects are N249 rat nest of hoses, the EVAP split hose that love to tear open, and the vacuum sources under the manifold.
With all that said, leaks are annoyingly challenging! Some of them don't appear until a certain positive pressure is reached. So you can have a system that looks fine at rest or idle and is a glorified strainer when operating at 10+ psi. So for that reason, the only solid way to test, find, and seal every leaks is to perform a good old pressure test. When doing this you should be pressurizing the system at least 5-7 psi above the boost pressure you run. The reason for this is that your charge piping is consistently seeing higher pressure than the manifold where most boost gauge vacuum source is taken from. So in other words, if you run 10 psi, pressurize the system to 15 psi when doing a pressurized leak detection test.
Ok, now that we've covered the idea behind it, this is what you need to do a professional pressure test. An air compressor with a decent tank capacity --- the typical 10 gal system you find in most home garage will suffice. A basic air pressure regulator with gauge (nothing fancy is needed). Some male/female air compressor fittings. Some PVC cap of some sort to plug into your charge piping system or TIP. 2" ID PVC joints will have the perfect OD for the hoses in the charge system (you can also pressurize at the TIP by disconnecting the MAF and plugging your tester there). You also need a flat nose vice-grip to clamp the PCV system (use the hose going to the head off the PRV valve). Also open the oil cap in case any pressure escapes your PCV clamp so you're not pressurizing inside the crank case. The pictures explains how to make a good tester and are worth a thousand words.
- Pop the bonnet open
- Remove the oil cap
- Clamp the PCV line
- Remove the MAF or rubber junction in the charge piping (closest possible to the turbo outlet)
- Plumb your tester and clamp it down securely
- Open your compressor valve all the way
- Set the pressure on the tester's dedicated regulator
If you've done this properly, the vacuum and charge piping will be pressurized and any leaks will be hissing loudly. The big leaks will be obvious and loud. Soapy water in a spray bottle helps find the very small leaks that might be difficult to locate just by listening. Seal all offending points until the car is leak free and hold pressure steady. Once finished the car will run better than it ever did with the turbo's work going to the motor instead of sipping out of unwanted leaks in the system. Discuss!!!