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2003 Acura sounds like a dying cow

Hi Ray and Tom,



My husband’s 2003 Acura TL sounds like a dying cow after turning off the engine, and has for at least 4 years.



He has had it into the dealership for a complete transmission replacement - free under warrantee.



It doesn’t seem to have any significant problems at 130,000 miles, but yet I do wonder why it moans like a banshee after being parked for hours.



Would love to hear back from you guys!

Tom & Ray don’t come on here to answer questions. 888-Cartalk if you want to talk to them. I’m not sure how to answer your question but here’s a nice little bump for your thread before it disappears in to the duldrums.

I think it’s a problem in the brake booster.

The booster has a vacuum reservoir that the engine’s intake system draws the air out of. Normally the reservoir holds vacuum for a long time after the engine stops, due to a one-way (check) valve.

My theory is that there’s a slow leak and the vacuum slowly goes away. WHen the vacuum is almost gone another valve in the booster “lets go” and lets a last gasp of air into the booster. The valve is made with a rubber diaphragm and vibrates like a whoopee cushion.

There are three tests you can do:

  1. Immediately after shutting the engine off step on the brake pedal once. It should feel as soft as when the engine was running.
    Start the engine again for a few seconds and shut it back off. Wait 5 minutes.
    It should still feel soft. If the pedal is real stiff there a booster vacuum leak.

  2. After stopping the engine repeatedly pump the brake pedal until it feels stiff. This removes all vacuum from the booster.
    Do this after every time you drive.
    If it no longer makes the sound then it’s in the booster.

  3. After shutting off the car disconnect the battery negative terminal. Wait for the sound.
    If it doesn’t make the sound then is probably something in the EVAP system.

Can you localize where the sound is coming from? Front/back/right side/left side? Without that information I am leaning toward the vapor recovery system. If too much pressure builds in the tank, a valve opens to vent gasoline vapors to the cannister. If a vacuum develops in the tank, the vacuum relief valve in the cap opens to admit air. If this noise happens regularily, you might loosen the gas cap slightly after turning the engine off and see if the noise disappears (of course tighten the cap before you start the engine again).

Also on some cars the vapor recovery system goes through a testing cycle when the car is idle. A pump will pressurize the tank which ordinarily does not cause an annoying sound. This test may occur many hours after the engine is turned off.

If you finally discover the source of this noise, post back so we can add the solution to our data bases.