Hi GUYS!! thank you all for this useful and beautyful forum; it's a bible for me here in Italy because nobody knows american cars!!

Can somebody tell me what the buzzy noise under the rear of my 88 iroc-z is?
it starts when i turn the (hot) engine off and goes on for 5/10 minutes.

thanks
Manuel
ITALY

 

It's like a humming sound right? It's the pressure in the gas tank...if you remove your gas cap, it releases the pressure and goes away. It comes back within seconds on my car as well. I was told that it could be the tank pressure check valve but I'm not sure yet.

 

does it do that on all of our cars? or is there any way to stop this completly?

 

yes, it is a humming noise.. i'll check ASAP if removing the gas cap it stops and i'll let you know!!

thank you LS7Roc!!!!

 

Fuel pump whine. Perfectly normal

Intensity is dependent on which pump is installed and the age of the unit

 

So, LS7Roc is right!!!!
after i turned the engine off the humming noise starts.. and ends if i open the gas cap; then closed starts again after 5 minutes...
Is it all about pressure and vacum, right?
When Pocket says it is the fuel pump whine he doesn't mean something electrical?

thank you ALL!
ciao

 

I've noticed that, if I loose just a little bit the tank cap, the whine never come on and, more important, the car run much better.
Is there any contraindication if I drill a very little hole in the cap to not let the tank go under pressure?

thanks

 

NO DRILLING IN THE CAP!!!!!!!!!!!! If it runs for THAT long after shutdown, you might have a F/P relay bad. It should last maybe 5 seconds or so; NOT 5 minutes

 

If it sounds about like something under the car is blowing its nose every minute or 2, then it's probably the vent valve aka "UFO".

Create the conditions that cause it to happen. Jack up the left rear and remove the tire. Just inside of the front LCA bolt, you'll see a white plastic thing maybe 60mm diameter. See if the noise is coming from that. If so, you need a new one. Sorry, no idea where/how to get one.

 

Is it normal for that much pressure to build up in the tank? Mine seems to have a lot of pressure.

 

Get a vented gas cap or replace the vent

 

It is not an electric problem! when I shut the car down the pump shuts off correctly.
It'is only about pressure/vacuum building up in the thank I guess..

 

Can i get the same effect by drilling a small hole in the cap?
Sorry but here in Italy is not so easy to find the correct parts..

 

I can't find the vent on my car. I do see a line at the driver side rear wheel area that has a rubber cap on it. I'm guessing that's where the vent goes.