Buzzing after shutoff
 

I am hearing a buzzing noise after I shut off my car. At first I hear it constantly, non-stop. Then after awhile it becomes intermittent, on-off-on type noise. And eventually it stops. The noise is fairly loud underneath the vehicle. Anyone know what could be causing this?

-James

1991 accord 4cyl 5speed EX.

Where under your Accord do you hear the noise?

Its loudest just below the gas tank. I am thinking it might be related to evap system based on that? I don't see any way the pump would be coming on and running with the key off although that's what it sounds like.

I think you have it nailed down. If you remove the gas cap does it release as if under pressure with a air noise?

I did check that after I got suspicious of the problem being evap related. and there was pressure in the tank. Unfortunately, I didn't do this while the buzzing was happening, it was about 15 minutes after it stopped and I thought about it. I'll probably have to wait until it does this again and try removing the cap to see if that fixes it.

Pressure released after removing the gas cap is a symptom it won’t fix anything.

Yeah, opening the gas cap won't FIX it. That's just to prove/disprove that it's related to the EVAP system.

In 1991 the EVAP canister is up front in the engine compartment. But there's hoses & fittings & stuff for the EVAP system back at the tank.

Yeah, I know that releasing the pressure in the tank won't fix it. I was just using that test to prove/disprove that it was EVAP related, or even related to the fuel system that was causing the problem. I know now that it is related to the evap system.

Check the DIY section for a sticky post about shop manuals. Get one for your year, that should have some good detail about all that EVAP stuff back at the fuel tank. You'll probably have to lift the back of the car & get down there to pinpoint the location of the noise.