I have a 98 Ram 1500 4x4 with a 318 engine. Within the last few months I've noticed a distinct hissing (maybe more like a sucking sound) when I accelerate. If I let up on the gas it stops or if I'm just maintaining my speed you can't hear it. Only when accelerating. If I tap on the gas pedal it's very distinct. Anyone have an idea what is causing this? A vacumn leak? Thanks for any suggestions.
Don

 

Sounds like your throttle body plenum. Make sure your air cleaner box isn't loose (that usually makes it sound louder).
It usually makes some noise, but it is muffled by your air cleaner. Sometimes, the gasket underneath the air cleaner will deterierate, or the air cleaner will become loose due to vibration, and you can start hearing the sucking sound more then usual.

Probably wouldn't hurt to have your throttle body cleaned too.

 

Thanks for the info. I'll check out the air cleaner when I get home tonight. I'm going from memory here but I don't remember a gasket on the air cleaner and the manual doesn't show one. Should there be one? Also, how do I clean the throttle body? Thanks again for your help.

 

Its not so much a gasket as it is a rubber ring. It is about 4 inches in diameter, made of rubber, and sits between your intake and your air filter box. They probably sell them in the parts department of your local dealership for less the $5.00. Last time I bought one it was between $3-$4.

The best way to clean your throttle body is to completly remove it. Once removed, any good injector cleaner should get it back to shape. Don't scrub it with anything abrasive. If you clean it while it is still on the intake, you basically just wash all that gunk right down into the intake. That's bad.

Good luck.

 

Mine makes the hissing sound as well but goes away after it warms up. Any clue why it would do that? Maybe the heat after warming up is making whatever surface is leaking expand?

 

If none of those other suggestions work, check your vacuum lines too.

My truck makes a hissing sound when it's near other cars or trucks like Mustangs, Camaros and Lightnings, then it promptly eats them.

 

Ya, heat expansion would be my first guess. Same way some exaust leaks go away after your exhaust has heated up and expanded.

I used to hear the sucking sound, then I tightened my air cleaner housing, and it went away. It was usually loudest when I first started the pickup. I have since removed the stock air cleaner, and put an Airaid intake system. The sucking sound is very noticable now because the Airraid system doesn't muffle the sound as much as the stock air cleaner box.

I kinda like it though. Sounds like the noise you used to hear when you would mash the gas with a big 4 barrel carb.

 

If it's hissing all the time, and you feel like you're loosing power, and the intake gasket and throttle body seem good it might be your catalytic converter OR your EGR valve...if you have a chilton manual for the truck follow the steps to check the EGR, if not PM me and i'll scan those pages and send them to you.

Good Luck-
--Dylan

 

i used the have the hissing, and it went away with a new cat. but then i also had that prob when i didnt put the air cleaner back on properly.

 

Mine's not only got a hiss...it's even got a little whistle![sm=icon_rofl.gif]

[sm=smokin.gif]
Quick;-)