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Fixing Common Vacuum Leaks
 
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Pelican Technical Article:

Fixing Common Vacuum Leaks

Jared Fenton

Time:

2 hours2 hrs

Tab:

$0 to $300

Talent:

***

Tools:

Screwdrivers, pliers, T20/25/30 Torx drivers

Applicable Models:

Volvo C30 T5 (2008-13)
Volvo C30 T5 R-Design (2008-13)

Parts Required:

New gaskets and seals

Hot Tip:

Check very carefully for leaks

Performance Gain:

Better running engine

Complementary Modification:

New spark plugs

This article specifically covers the Volvo C30, however the concepts I'll go over apply to nearly all fuel-injected gasoline engines. In a gasoline engine, the speed of the engine is controlled by the amount of air that enters through the throttle body. In a diesel engine, there is no throttle body. The speed of the engine is controlled by the amount of fuel injected into the cylinders. Diesel engines are a different animal that we will cover in a different article.

A poorly running car can often run amazingly well after an afternoon's worth of work, going through the various rubber boots and hoses around the engine. Vacuum lines, intake boots, seals and many other small gaskets around the engine can be the source of poor running and idle problems

Many times, a lean running condition can be traced back to a cracked or torn boot in the system. A good quick way to check the overall health of the system is to take the oil filler cap off with the engine running. If the system is in good shape, the idle of the engine should drop and the car will run rougher. This is due to the extra unmetered air flowing through the oil filler port. If there is no change in the vehicle's idle, then you probably have a vacuum leak somewhere in the system. Don't forget to check places where vacuum leaks may not be as obvious, such as the oil filler cap, the dipstick and also the valve cover. A quick way to check for a vacuum leak is to spray a little bit of carburetor cleaner around the engine at various places and see if the idle changes. If it does, you know you have a vacuum leak in the general area in which you sprayed.

You'll also want to inspect the crankcase breather hoses. It's not uncommon to have these plastic lines crack after years of heat cycling in the engine compartment. This typically results in very rough running at idle. Over time, this can result in problems when trying to get the car to pass an emissions test. The good news is that the hoses are easy to replace. However they can be a bit expensive. See our article on Replacing Crankcase Breather Hoses for more information.

Another often overlooked place for vacuum leaks are the throttle body and upper intake plenum gaskets. Over time, the environment of the engine compartment can degrade these seals. Typically, these will result in idle fluctuation and overall poor running.

Start by checking the bellows (green arrow) that connects the upper intake pipe to the air filter housing.
Figure 1

Start by checking the bellows (green arrow) that connects the upper intake pipe to the air filter housing. Also check the intake hose (yellow arrow) connecting the other end to the turbocharger and the hose assembly for the brake booster system (purple arrow).

Listen for any leaks coming from the crankcase breather hose (green arrow) and the accompanying lines in the area.
Figure 2

Listen for any leaks coming from the crankcase breather hose (green arrow) and the accompanying lines in the area.

One other often-overlooked place that can develop vacuum leaks is the small seal on the inside of the oil filler cap.
Figure 3

One other often-overlooked place that can develop vacuum leaks is the small seal on the inside of the oil filler cap.

Shown here are the five gaskets (green arrows) that fit on the underside of the intake manifold.
Figure 4

Shown here are the five gaskets (green arrows) that fit on the underside of the intake manifold. See our article on Upper and Lower Intake Manifold Removal for more information. The throttle body seal (yellow arrow) can also be a source of leaks. See our article on Throttle Body Cleaning for more information.

Don't forget to also inspect the intercooler hose feeding the throttle body (green arrow).
Figure 5

Don't forget to also inspect the intercooler hose feeding the throttle body (green arrow). Years of heat and pressure can eventually damage the hose resulting in a loss of power.

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Page last updated: Fri 12/9/2016 02:38:25 AM