How To Check For Vacuum Leaks (1995, 1996, 1997 2.2L Accord, Odyssey, And Prelude)

Vacuum leaks can and do have adverse effects on engine performance and the fuel injection computer's ability to reduce harmful emissions.

Eventually, a severe vacuum leak will cause the check engine light to illuminate with air/fuel mixture trouble codes (for example: P0171, P0172, etc.).

In this tutorial, I'll explain the 3 types of tests that can be done to find the source of the vacuum leak.

You can find this tutorial in Spanish here: Como Encontrar Fugas De Vacío (1995-1997 2.2L Honda Accord, Odyssey) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

  1. 2.2L Honda Accord (DX, EX, LX): 1992, 1993, 1994, 1995, 1996, 1997.
  2. 2.2L Honda Odyssey: 1995, 1996, 1997.
  3. 2.2L Honda Prelude: 1992, 1993, 1994, 1995, 1996, 1997.

What Is A Vacuum Leak?

In a nutshell, a "vacuum leak" refers to air entering the engine at any point after the throttle body.

This air should not be entering the engine, since it will disrupt the air/fuel mixture the fuel injection computer is trying to control.

To go into more specifics: The fuel injection computer measures the amount of air entering the engine after it has passed the throttle plate (in the throttle body).

It then calculates the amount of fuel to inject into the cylinders for that amount of air.

The fuel injection computer will inject 1 gram of fuel for every 14.7 grams of air. This ratio of air to fuel is known as the stoichiometric air/fuel ratio (14.7:1).

Any air that enters after the throttle plate (caused by a vacuum leak) will raise the air to fuel ratio and will cause the engine to run leaner (leaner = less fuel).

This leaner air/fuel mixture can cause engine performance problems and turn on the check engine light on your Honda Accord or Odyssey's instrument panel.

Vacuum Leak Detection Basics

There are plenty of places for leaks to pop-up on the 2.2L engine, but you should always start by visually checking the condition of the engine's vacuum hoses.

It's important to consult the vacuum hose routing diagram of the vehicle emissions label (on the vehicle's hood) and check:

  1. The condition and fit of each vacuum hose. The vacuum hoses should have a tight fit around the metal line or vacuum port that they're connected to.
  2. Vacuum hose routing. This involves making sure they are connected to the correct component or vacuum port.

If your Honda Accord (Odyssey) is missing the vehicle emissions label, you'll need to consult a repair manual.

If the engine's vacuum hoses are OK, and you still suspect a vacuum leak, then you'll need to perform a vacuum leak test with carb-cleaner, or propane, or water.

Using Carburetor Cleaner To Find The Vacuum Leak

Using a carburetor cleaner spray (mostly known as air intake cleaner nowadays) to locate a vacuum leak (especially around the throttle body gasket area or intake manifold gasket areas) is a very old mechanic's techique.

It works this way:

  1. The engine is started.
  2. As the engine idles, carb-cleaner is sprayed onto/around the suspected vacuum leak areas.
  3. Wherever a vacuum leak is present, the carb-cleaner will be sucked into the leak.
  4. This will cause the air/fuel mixture to stabilize and you'll notice a very discernable change in the engine's idle.
  5. Wherever the spraying of carb-cleaner causes a noticeable change in the engine's idle, that is the area with the vacuum leak.

Yes, spraying carb-cleaner around a hot engine can be dangerous, since a hot exhaust manifold can make the carb-cleaner light up.

To mitigate this risk, perform this test with a cold engine. Once the engine has reached its normal operating temperature, you should no longer continue spraying carb-cleaner.

Also, it's important to use short sprays of carb-cleaner, instead of a continuous spray, around the suspected vacuum leak area to localize the leak.

Using A Propane Torch To Find The Vacuum Leak

Using an unlit propane torch to locate the source of the vacuum leak is another very common test (one that I've used myself many times).

It works this way:

  1. A hose is placed over the propane torch's outlet nozzle.
  2. The engine is started.
  3. As the engine idles, the propane torch is opened and propane is released onto/around the suspected vacuum leak areas.
  4. Wherever a vacuum leak is present, the propane will be sucked into the leak.
  5. This will cause the air/fuel mixture to stabilize and you'll notice a very discernable change in the engine's idle.
  6. Wherever the release of propane causes a noticeable change in the engine's idle, that is the area with the vacuum leak.

This test also requires that it be done with an engine that is cold. Once the engine has reached its normal operating temperature, you should stop the test.

Using Water To Detect A Vacuum Leak

Spraying water around suspected vacuum leaks is another common way to localize a vacuum leak.

It works this way:

  1. The engine is started.
  2. As the engine idles, water from a water spray bottle is sprayed onto/around the suspected vacuum leak areas.
  3. Wherever a vacuum leak is present, the water will temporarily seal the vacuum leak.
  4. This will cause a very discernable change in the engine's idle.
  5. Wherever the spraying of water causes a noticeable change in the engine's idle, that is the area with the vacuum leak.

More 2.2L Honda Accord And Odyssey Tutorials

You can find a complete list of 2.2L Honda Accord and Odyssey tutorials in this index:

  1. Honda 2.2L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

  1. How To Test The MAP Sensor (1994-1997 2.2L Accord, Odyssey, Prelude).
  2. How To Test The Head Gasket (1992-1997 2.2L Accord, Odyssey, Prelude).
  3. How To Test The Engine Compression (1992-1997 2.2L Accord, Odyssey, Prelude).
  4. How Often Should I Replace The Spark Plugs? (2.2L Honda Accord).
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