Diagnosing and Repairing a Vacuum Leak
The environment in the engine compartment is rough, affected by motion and heat. Over time a leak can happen in one of the vacuum lines. You will first want to isolate the faulty line which can be identified by a hissing sound.
Vacuum leaks can cause extra air to flow into the system throwing off fuel to air balance that’s critical to fuel function. This will turn on the check engine light.
IS A VACUUM LEAK THE PROBLEM?
If something has caused your check engine light to register, it’s best not to presume it’s the sensor that’s at fault. For instance, a vacuum leak at the EGR valve can be enough to prevent the solenoid from opening and closing the valve, causing a trouble code to be stored. A vacuum leak at the MAP sensor might disrupt engine timing strategy and fuel delivery, causing fuel economy and drivability problems. Same goes for emissions systems like the EVAP canister and others. Your braking system could also be affected by a vacuum leak, since most power brake boosters rely on engine vacuum.
Do not presume the worst or go after the most complex and expensive problem unless you’ve first ruled out a vacuum leak. Symptoms like poor acceleration, rough idle, stalling, stumbling, misfires, poor fuel economy, and hard starting might be caused by nothing more than a vacuum leak.
FINDING THE VACUUM LEAK
- Locate the vacuum schematic for your vehicle. In many cases, there will be a sticker under the hood that will show vacuum line routing, or your service manual.
- If your trouble code is related to fuel metering, the engine control computer may already have compensated to adjust for the change in air/fuel ratio. In that case, disconnect the throttle position sensor (located at the throttle body) to force the engine into “open loop” mode. That way you can hear it rough-idle and it should be easier to track down the vacuum leak in question.
- Being mindful of hot surfaces and moving parts before you start an inspection of each vacuum line, including its T’s and junctions. Vacuum lines are fairly thin and soft, some not much bigger than a drinking straw. Look for splits, tears, flared-out ends, and splits at the ends. An inspection mirror and flashlight helps to see difficult areas.
- It will be harder to listen for the hiss of a vacuum leak over the noise of an idling engine, but a mechanic’s stethoscope (or even a length of hose) can make it easier to amplify and isolate a noise.
- Feel for softened spots, hardened spots or deformed spots along the length of each line. If you’re lucky, your fingertips might even be able to feel suction from a leak.
- If you find a vacuum line that’s split at the end, you may be able to snip off the end and reconnect. For many hoses, this is not an option, though, as the length from the factory is specific to the application.
Andress Auto Parts is your one stop shop for fixing your vacuum leak. Speak with one of our experts today.