Fueling related - Humming from rear right strut under load

[ciper]

So I have a strange problem. There is something in the rear right strut area that hums/buzzes but only under slight load. I can rev the engine in neutral but it doesnt make the noise. If I am rolling with the engine off it doesnt make the noise. Keeping my speed constant (say 5mph) and then changing throttle position changes the pitch of the noise slightly. It is mostly independent of speed and isn't a brake thickness warning tab.

It sounds like a reed valve on a wind instrument. My wild imagination says there is some type of valve that helps fuel return to the tank and its near the filler neck and it has failed in a way to make this noise?

Help me to brainstorm. Thawa was in my car and folded the rear seat down and he said he could feel a slight vibration in the area of the right rear strut

Maybe its not fueling related but it seems to not be drivetrain related and I can't think of anything in the back of the car that is somehow connected to the engine...

[legacy92ej22t]

I don't know or have any ideas really but HEY! What's up ciper, how you doing man? Hope life is treating you well.

and did I hear Thawa? WTF? What happened to him? He fell off the earth. lol

[ciper]

He has become quite the Subie repair guy. He's still involved in his own project Subarus in some form or another but like me spent free time either talking to people in real life or doing non car things.

[Legacy777]

Is the hum you're hearing coming from the fuel pump?

BTW, good to see you on the boards again.

[ciper]

I will have to double check that but I thought the fuel pump was more in the middle?

I wish I had seen your post about the Cali road trip earlier because you could have came over to the shop in SoCal or my place or NorCal!

[Legacy777]

Fuel pump is on the passenger side. You can see the two access ports on the tank in this picture

http://www.surrealmirage.com/subaru/ima ... P_3118.JPG

Yeah I was wondering if you had seen it. I tried sending an email to your hotmail account in December, and don't know if ever went through or not.

[subbawho]

If you suspect the fuel pump. Take the fuel pump cover off. Have someone drive it and have someone listen to the fuel pump with a stethoscope or a 3/8 extension and put your ear to it or if you don't have another person with you. Raise it so no wheels touch the ground and put it into gear. Yes the abs light will come on but it will go off after you shut it off and put the car on the ground.. Since you said it changes noise from throttle position. It's very well possible it's the pump. Since your giving it throttle. It's changing the amount of fuel pressure thru the system. Does the pitch get higher or lower? Let me know. I love figuring out stuff like this hhaha

[ciper]

Its not the fuel pump. Its this -



What the hell is inside that upper box? The picture is of the right side strut tower inside the trunk

I had someone drive while I took the car apart lol

[Legacy777]

It's the fuel separator. There are no moving parts. Unless something is loose, or a vacuum line is loose (but then you'd smell fuel)

Here's pics of mine during my AWD & 5spd swap.

www.surrealmirage.com/subaru/images/swap/07

Here's pics of a wagon separator.

http://www.surrealmirage.com/subaru/ima ... P_3100.JPG

Two lines go to the top of the tank, and the other line goes to the charcoal canister.

[ciper]

At one point I did say to my friend it sounded like a reed from a wind instrument. Maybe there is a small leak?

[Legacy777]

Could be. I'd try removing it and check it out. The metal cover should be able to be easily unbolted.

[ciper]

I figured out whats happening but not exactly why.

When i installed the 2.5 engine I got rid of the charcoal canister. I took the vacuum line that runs from the purge solenoid and connected it to the intake manifold.

It was fucking hard to diagnose because the ECU closes the purge valve the instant there is no signal from teh speed sensor! So i had to be moving at least 1mph for it to make the sound lol.

I put a nail inside this vacuum line to plug it up temporarily. The fuel separator container was acting like a reverb chamber amplifying the vibration caused by something else.

This leads me to an idea. It seems that the purge solenoid is open at all times, or at least between 1mph and 25mph where I could hear the sound. Should we try to place a filter on the charcoal cannister to reduce the amount of dirty air that must be entering it?

[Legacy777]

That's very interesting.

I have removed the charcoal canister and plugged the lines coming from the separator & intake manifold when I put in my stand alone ECU. I have the ability in the Link to add a canister purge output. I was going to try leaving the charcoal canister off and hooking the two vacuum lines together.

However that sounds like it may have issues.

As for your question, I'm not sure I get it. The charcoal canister is sealed, there should be no air entering it.

[ciper]

The charcoal cannister isn't sealed. There is a hole on the bottom, usually with a little tube

[Legacy777]

Yes, but have you ever tried pressurizing it through the vacuum lines? It holds pressure.

[ciper]

Yes, it holds positive pressure but I don't think it holds vacuum.

[Legacy777]

Haven't tried testing vacuum.

[ciper]

I mean I guess it is filled with charcoal which is a pretty good filter but I'd imagine that over time it would get all clogged up with dirt.

I was thinking - what if I used a vacuum line with a restrictor pill like what goes to the boost control solenoid on a WRX. That might allow me to get rid of the charcoal cannister and also not get the hum?

[Legacy777]

I still don't know how you would really get dirt in there....I just don't see it happening.

As for the restrictor pill. That may work.