Full Size Jeep Network

I just had the Howell TBI installed in my '76 Wagoneer. Did not do it myself; had my mechanic do it.

Truck appears to be running very well, but I now hear a new sound in the cab. It's a low hiss (sounds like air, maybe) and it gets louder when I compress the gas pedal. Is that normal? It's definitely in the cab and not a wheel sound - makes the sound at idle in parked position.

I know there are components to the system in the cab. It's a little annoying, so I'd love to be able to put a stop to it.

What model Jeep is this It sounds like you have a cab vacuum leak,

If you switched from the factory enclosed air cleaner, to an open element air cleaner, it will sound different. The open element will sound like more carburetor noise.

Serehill - it's a 1976 Wagoneer; AMC 401; Howell fuel injection; MSD hei distributor.

I just had the Howell fuel injection and the distributor installed.

Almost sounds like and exhaling breath that is louder when the gas pedal is engaged.

Yeah I would trace it out. it does sound like a vacuum leak but could be carburation as suggested. There are several vacuum lines under the dash of that model. If you only hear it in the cab then I would search under the dash around the glove compartment & over by the heater switch.

I did a bunch more Googling and it seems that the hissing sound is just the sound the injectors make on the Howell TBI. People seem to say they stopped trying to "fix it" and that it's "normal."

I did read that one way to silence this sound is use some kind of snorkel air box type thing.

Sounds like I just need to get used to it.

Most carbs/TB setups with an open element air cleaner have a very audible intake sound. My J10 hisses at low idle, and had a very deep sound at higher throttle levels.

Stuka - is the way to quiet this a different kind of air cleaner? CAI? Some other kind of air cleaner?

Yeah, you basically need something that will muffle the intake sound. On late model cars this is with an air box, which acts as a muffler. There are setups that will connect to the top of the TB and then rub tubing (like a newer car) out to the front passenger side of the engine bay, and put the air cleaner there. This will quiet it down a lot. You will still get some of the lower tones associated with heavy acceleration, but none of those higher pitched sounds that you are getting now.

My truck did this after converting to TBI and using an open element. I hated it, put the factory snorkel back on and no more noise.