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Pelican Technical Article:

Vacuum Leak Test

Time:

1 hour1 hr

Tab:

$1180

Talent:

*

Tools:

Smoke Pro, compressor

Applicable Models:

 
Porsche 911 (1965-74)
Porsche 911 Carrera (1974-89)
Porsche 911E (1969-73)
Porsche 911L (1968)
Porsche 911S (1967-77)
Porsche 911SC (1978-83)
Porsche 911T (1969-73)
Porsche 930 Turbo (1976-77, 1986-89)
Porsche 964 Carrera 4 (1989)

Parts Required:

Smoke Pro

Hot Tip:

Preform this test out of the wind

Performance Gain:

Proper running motor

Complementary Modification:

Injector O-rings

The horizontally opposed flat six cylinder engine in the Porsche is legendary; from its accomplishments on race tracks around the world to its longevity in street cars. There is nothing more magical than the sounds of a finely tuned 911 at full song. Unfortunately these engines do fall out of tune and it does not take a lot to have them start running rough. When your engine starts to run rough there are the three areas you need to check; fuel, spark and oxygen. Since the 911 motors are famous for vacuum leaks, and even a little unmetered air can have profound effects on the motor, doing a thorough vacuum leak test is very important. If you are tired of rigging up a ShopVac in reverse, spritzing the seals with soapy water or the potential danger of spraying carb cleaner around a running motor then you should consider investing in a Smoke Pro (you will also need a small compressor if you don't already have one). It makes what can be a difficult and frustrating job simple and quick.

You are going to be looking for where any smoke is coming out of the motor so you want to perform this test in an area where it is not windy to help you pin point the leak. DO NOT run the motor while performing this test.

There are many places you can hook the Smoke Pro up to but the easiest is the vacuum line (yellow arrow) from the WUR or the pop off valve (red arrow).
Figure 1

There are many places you can hook the Smoke Pro up to but the easiest is the vacuum line (yellow arrow) from the WUR or the pop off valve (red arrow). It is best to start with the WUR line as the pop off valve can be a source for vacuum leaks, but if you know the pop off valve is good you just lift it up and stick the adaptor and hose in. You will need to stuff a rag into the area around the metering plate to contain the smoke in the throttle body (green arrow).

The Smoke Pro pulls its power from the car.
Figure 2

The Smoke Pro pulls its power from the car. Attach the positive clamp to a good power supply in the rear fuse panel (red arrow) and the ground to the engine compartment ground (green arrow).

Plug the Smoke Pro into a compressor.
Figure 3

Plug the Smoke Pro into a compressor. There is a built in pressure regulator in the machine but keep you compressor below 40 lbs. Once the green light is on press the start button (green arrow) and the machine will smoke for 5 minutes. You can control the amount of smoke the machine puts out from a little to a smoke screen (yellow arrow).

Areas to check for are the O-rings around the injectors and sleeves (yellow arrows) as well as the rubber boots on the intake runners and air box (red arrows).
Figure 4

Areas to check for are the O-rings around the injectors and sleeves (yellow arrows) as well as the rubber boots on the intake runners and air box (red arrows).

You want to check for smoke emanating from the plumbing and connections on the rear of the air box (yellow arrow).
Figure 5

You want to check for smoke emanating from the plumbing and connections on the rear of the air box (yellow arrow). The vacuum system is tied into the sump; look for smoke leaks around the oil cap (red arrow). This is one of the most commonly over looked areas for leaks but an improperly sealed oil cap can cause your engine to run rough.

The right side of the motor is a little more difficult to check for leaks.
Figure 6

The right side of the motor is a little more difficult to check for leaks. Take a flash light and look carefully around the injectors (red arrows) and the intake runners and air box (yellow arrow).

Ah ha, found it.
Figure 7

Ah ha, found it. The injector seals are a common place for leaks. Please see our article on replacing your injectors, O-rings and sleeves if this is where your engine is leaking from.


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