Loud hissing noise


Vanner1993

Vanner1993

15+ Year Member

Joined
Nov 26, 2009
Messages
270
Points
3,101
City
New Jersey
Vehicle Year
1983, 1977
Transmission
Manual
I was on my way home just about putting it in 3rd gear and either under the dash or under the truck a hissing noise started. For some weird reason as I was listening to the noise trying to get home, the fuel gauge dropped...I thought oh crap a fuel line popped off. Got in my driveway, no fuel leak or any other signs of a problem. The hissing mostly diminished and stopped. Shut the truck off, restarted and checked gauges, fuel was at half tank where it should be and no noises. What? I am confused here...
 
Coolant level ok? Hissing noise can be either a vac line, or escaping coolant.
 
The coolant is good, it wasn't hissing when I was stopped in my driveway or when I reved it in neutral. Just started loud then got quiet and stopped. And the fuel guage went with it, when the hissing was loud, the fuel guage dropped as if I popped a line off, when the hissing stopped the fuel guage was where it should be.
 
Well, popping a line shouldn't make the gauge drop out like that, but it would probably kill the engine, so not sure what you mean by 'fuel gauge dropped as if I'd popped a line off'.

That is really weird though.
 
if a line popped off, it pumps the gas out.. making the gauge show E


but i dont think it would pump a half tank out that fast..
 
Yeah the gauge dropped slowly to E with the hissing noise. Went back to normal after I parked, shut off and restarted. And as I was driving I was thinking the same thing, no way did I just lose half a tank of gas behind me...
 
It was a snake chewing on the back of your fuel guage. I got nothin man.:dunno:
 
Bad ground or shorted wire will sometimes make a w-e-i-r-d noise.....especially in the gas tank!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
Ive been having the same hissing noise like you talk about, and my gas gauge stopped working too a month ago. The noise will usually start when i start it up and wont go away until the trucks warmed up and been running for a while. The gauge will sit at around 1/2 tank when the truck is off and will slowly work its way to empty when I start it up. The hissing noise has been going on for much longer than the bad gauge.

I don't notice any affect on power from the hissing, and the idle is smooth at around 600-700rpm, so If it's a vacuum leak it must be a small one since it doesn't affect the idle much. I've just been trying to figure out what the problem is and have had no luck so far.
 
Vanner1993 said:
Yeah the gauge dropped slowly to E with the hissing noise. Went back to normal after I parked, shut off and restarted. And as I was driving I was thinking the same thing, no way did I just lose half a tank of gas behind me...
Click to expand...

in my 88, i was driving late one night, and i pulled the high beam lever, it hissed for a second, then every electrical system in the entire truck died, headlights went off, radio shut down, engine quit firing.

punched the dash a few times, pulled the high beam lever a few times, and punched the dash again and it all came back up.

best i can tell you is a loose or grounded out wire.
 
Is there a main ground wire for under dash? Because if I take a quick sharp turn the passenger speaker kicks on as if it has a loose ground, that may be why my gauges are acting funny. I'm gonna look under the dash today.
 
The plot thickens...more info has been given........
 
Ok I found out the reason for the fuel gauge moving and lifting. When I am under a half tank, the littlest movements splashes the gas around...stupid me haha. The hissing is the exhaust, I must of blown a gasket on the pipe out. It is under the cab around the Y pipe.
 
4.0B2 said:
if a line popped off, it pumps the gas out.. making the gauge show E


but i dont think it would pump a half tank out that fast..
Click to expand...

If a line pops off, the engine dies and the computer, not seeing an engine rotation signal, shuts off the pumps.

Also, it's been a while since I looked up the flow rates on these pumps, but IIRC it would take several hours to pump a half tank dry just flowing it out the lines.
 
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