Hi, new to the forum, have seen some great questions and answers here,
and have one that stumps me. My 98 LX can sit for hours turned off, key
out, ect, then all of a sudden it will start humming like the fuel pump is coming on.
It'll hum for about 3 seconds and quit. It might do it again 10 minutes later and so on. Anyone have any idea what's going on?

 

No idea. Can you narrow down the location of the sound?

 

Does it have an aftermarket alarm or remote start?

 

It's coming from underneath next to the fuel tank. No alarm or remote start. Sounds just like the fuel pump coming on and up to pressure and cutting off.
Problem is the car isn't even on, even no key in the ignition. Just HMMMM
for a second or two then stops. Will do it again 10 minutes later. Crazy I know,
what controls the fuel pump?

 

When you turn the key on, the ECU switches onthe fuelpump side of the main relay for 2 seconds. That's basically part of the ECU startup sequence.

Do the dash lights come on when this happens?
If a flaky ignition switch turns power ON to the ECU, then the CEL would also come one for 2 seconds. If it's a flaky main relay, then something else is going on.

Maybe you'll have to trace back 'upstream' to see where the power is coming from, and what's causing it to come on.

 

Maybe the gas tank is warming up andexcess pressure is venting thru the purge?

 

Along with JimBlake's comments....

Unplug the 3-pin power connector for the fuel pump when you hear the sound. If the sound stops, then somehow you are getting power at the fuel pump. Then you'll have to trace backwards.

 

Quote : Maybe the gas tank is warming up andexcess pressure is venting thru the purge.

That may well be it. I got someone else to key the ignition while I stood outside. The actual sound of the fuel pump is almost inaudible. This is my first Honda and I've only had it about a week, so I'm learning the quirks. Filled the tank up last night and haven't heard the noise???

 

That EVAPcanister is locatedunder the left side of the car, sorta under the left-rear seat. The vent is on the outboard end of the canister, so it's pretty close to the rocker panel. (Pretty close to where you putthe tire-changingjack for the left-rear. If you get close enough to hear it, try to distinguish the location vs. the fuel pump which is more to the middle of the gas tank.