smitty2919

I ended up putting my stock TB/plenum back on the car couple days ago. Well under 1/4 throttle load, I notice this sucking noise coming from what it seems to be behind the dash and or the passenger side engine bay. This is from my hearing while driving. There is one tube in question that runs from the back of the throttle body at the base of it that runs down the passenger side of the car. It has "gas/fuel" or something written on it.

The reason I say it's in question is because it is pretty well dry rotted and any time you bend it, it literally flaks the outer layer of rubber off. I've checked the other vacuum lines in that area and they all seem fine.

I was wondering if there is any other lines that it could be causing this sound. That tube I referenced, anyone know what it's for? I looked in my shop manual on TB/plenum to see if they told me the hose name, but it said "remove this tube" with a arrow pointing to it LOL.

Thanks for any ideas guys

Harryman2002

When I got my TB it always had a noise like that just cause thats the kind of noise it makes, does your car run bad at all or is it just the noise?

uberstang1

I beleive the line you are talking about is the rubber hose for the EVAP system. Is it black with a red stripe? This line runs from the plenum to a solenoid then to a sensor then to the charcoal canister located inside the passenger fender. It is notorious for rotting out, I had to change it on both mustangs I've owned along with a couple of my friends. Sometimes a fuel smell will be incorporated with a leak.

cliffyk

That's what it is--look in the evaporative emissions sections of the shop manual, though it's only shown in flow diagrams...

smitty2919

Thanks for the replies.

Harry: It's my stock TB and plenum so it shouldn't me making this kind of noise. My PP TB/plenum made that kind of noise

Uber: Thanks for the heads up. I'm looking to his up Autozone to get a length of hose to replace it and go from there. I went to Pepboys but they were out of that specific 3/8" ID hose.

Cliff: Thanks I'll take a peak into my shop manual again for the vaporative emissions sections.

smitty2919

Ended up replacing the whole line from th back of the plenum through the passenger fender to the EVAP canister purge valve behind the fender liner. But the noise still remains! Dun dun dun!

Still does it under a certain amount of load, anything more or less than the given load, you don't hear it. Which is strange if you ask me. So any other ideas of possible/prone lines to cause a leak I'm all ears.

uberstang1

Did you use new gaskets for the TB and the plenum?? also do you have a good seal from the intake tube to the throttle body?

smitty2919

I did not use a new seal from the plenum to TB. The gasket from the TB to plenum is the stock one and I don't think I ever took them apart. The Intake tube is on tight and sealed up.

I'm paying more attention to it and I can get it to make the noise at any time. If you are accelerating and you ever so slowly depress the pedal it will not do it. If you are easing on the pedal and you go any quicker, I guess best way to describe it is a "stab" of the pedal, it will do it. In any gear, at any rpm, at any speed you can do it.

It didn't hurt that I replaced the tubes going to the EVAP canister as both of them were pretty dry rotted, but apparently not leaking. Next will be a tb/plenum gasket. I would love to throw it on a dyno and run it that way while someone sticks their head under the hood. I also thought about jacking the rear end up and staying in first gear then stab at the throttle to have someone listen for it. But that may not promote enough load on the car. It could be the same as reving in neutral with the car on the ground.

uberstang1

So in otherwords if its in neutral and you just full the throttle blade open quick to simulate the "stab" of the pedal it doesn't make any noise? If it only does it with a load on the tires and car I doubt its a vacum leakor a bad plenum gasket as those leaks would be present regardless of load.

smitty2919

When in neutral, and you pull the throttle, all I hear is the sucking coming from the plenum(I'm under the hood). I see your point though. But like I said it will do it cruising and when you depress the pedal slightly faster for 1" of travel or so. It's hard to explain sorry if that doesn't make sense.

I replaced the TB to plenum gasket last night, and sprayed carb cleaner all over the place to no avail.