bbilt

I have a random hissing noise, not at idle but when I'm driving. Its totally random. I've looked for leaks and found none. The 93 D250 with 260,000 runs great no changes. It has better get up and go than my 92 w250.
Any ideas on what it could be or where to look?
Thanks Guys

MrFusion

Partially clogged fuel tank vent?? Tank builds enough pressure from heat due to returned hot fuel and ambient temp to push through a clogged vent and make a hissing noise? Just a wild guess on my part.


Maybe something A/C related?

thrashingcows

Check your brake booster piston under the dash, it could be sucking vacuum around the seal. Fire the truck up and then lay on the floor and push/pull/wiggle the brake lever and see if you can hear any leaks.

nonrev

Wow, in my truck you couldn't hear a 400lb tiger sitting next to you hissing when going down the road lol

Angry Johnny

Spoken like a true 1st gen owner. I wonder why I even bothered to put a radio in it.

NJTman

The funniest part is when you pull up behind a little old lady, and they think you're too close to them, when in reality you're a car length behind, stopped at a light.


They can't stop moving up, and looking in their mirrors for where all that racket is coming from.

peckens

I would check the booster boot under the cab. Could be a vacuum leak

MrFusion

Angry snake stuck under the dash somewhere? Maybe he chased a mouse in there and ate it. Now he's too fat to get out the way he came in.

bbilt

I think I found it , the botttom of the inter cooler boot has a small slit. Looking for a new set. Didn't see them in geno's for a 93 ?

oliver foster

That explains why it only makes the noise when on the road under load.

You can find a set on siliconetubes.com, IIRC or other websites. I had a hard time getting a reply back from them when I needed some custom sized boots though.

Or, I have several good, OEM used boots in the shop if you need as well. PM me if you would like.