Hey guys,
I just got my first TPI car, a 91 Z with the 305. This might be normal, but I kind of doubt it. When its parked, as in stopped and the engine not running and the key completely removed, there is an odd humming noise coming from the back of the car. It sounds like a deeper pitch than when the fuel pump primes the system when you turn the key on, and only lasts for 1 to 2 seconds. Any ideas what it could be?

Brian

Only thing back there is the fuel pump.

Yes, I understand the only thing back there is the fuel pump, but it is normal for it to be doing this?

It's normal for it to humm for a few seconds when you shut the car off...there's an oil pressure bypass switch that supplies power to the pump...so when you shut the car off the pump will still run until the pressure falls below 2-5PSI (unsure of exact number).

Now if it's humming all the time, might want to look at replacing the bypass switch...

If it's not the FuelPump, only other device I could think of is the hatch motor.

Thanks Mike, I plan on replacing the sending unit and see what happens.

Brian

It is not the fuel pump or the sending unit.

If you look just inside of the left rear wheel, you'll see a little plastic valve. That's what does it.

Only place to get one AFAIK is the dealer.

Want to guess how I know that?

And what is that little plastic valve and what does it do?

Brian

It's the pressure relief for the gas tank.

I had the same thing happen on my 88 TA. Everytime you shut the car off after driving it, or even on warmer days....the car would just sit there and hum...much like a fuel pump. Everytime I would go over and loosen the gas cap, the noise would go away. Go to the dealer and buy a new relief valve.

Ok, thanks guys. Is this something that will/could cause me major problems? Cant afford to get it fixed right now ...

Brian

Youll be fine, its just more of an annoyance than anything else.

Ok cool, thanks. From my experience, the local GM dealers havent been very .... usefull in finding parts and getting them for me. Anyone happen to have a part number I can give them, or will they actually know what I need? THanks for the help guys

Brian