What are the symptoms of a vacuum leak?

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Common Symptoms of an Engine Vacuum Leak:

Engine vacuum leaks are commonly related to the subsequent symptoms, but this can not be an exhaustive list.

 

Engine Running Problems:

An engine with a vacuum leak could potentially run normally, but it should idle faster than usual, idle roughly, misfire, hesitate or stall. You’ll find your vehicle doesn’t accelerate furthermore as it typically does. Major intake leaks might prevent the engine from starting.

 

Fuel Economy and Emissions:

The lean air-fuel ratio will burn hotter and increase the generation of oxide emissions, like pollutant (NOx) and sulfur oxide (SOx). Whether or not the check engine light isn’t triggered, the vehicle should still fail emissions testing. Drivers would also note reduced fuel economy because the engine controller attempts to compensate by adding more fuel. The evaporative emissions system (EVAP) also depends on the vacuum to function, so a vacuum leak in an EVAP valve or tubing might set an emissions diagnostic trouble code (DTC).

 

Check Engine Light:

The engine control module (ECM) continuously monitors the environment within the engine. Using the manifold absolute pressure (MAP) sensor or mass airflow (MAF) sensor, among others, the ECM modulates fuel injector pulse, spark timing, and valve timing. If there’s a vacuum leak, the ECM is also unable to compensate. Short-term or long-term fuel trim, STFT or LTFT on a scan tool, might show something like +10% or +25% because the ECM attempts to complete unmetered air. P0171 and P0174 are common equipment in Lean DTC.

 

Engine Damage:

At its worst, long-term driving with a vacuum leak, elevated temperatures generated by running a lean air-fuel ratio could end in engine damage. Lean mixtures can detonate, damaging pistons and bearings. Beyond normal exhaust temperatures also can result in converter meltdown.

 

Other Issues:

Depending on where the vacuum leak is found, it could cause a spread of other problems. Some fuel pressure regulators are vacuum modulated, then would jump to air mass when the vacuum is lost. This might end in fuel trim problems and a check engine light, possibly with equipment Rich DTCs (Diagnostic Trouble Code), like P0172 or P0175. Some older steering system systems idle-up the engine employing a vacuum switching valve (VSV), but a vacuum leak might stall the engine during a parking maneuver. Many vehicles use a vacuum-actuated brake booster, reducing braking effort, but a vacuum leak here might make it harder to prevent your car.

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