I Have A 99 F250 6speed W/magnaflow 4'' Exhaust(no Cat) And While Driving Truck If I Just Give The Truck A Little Throttle I Hear A Weird Exhaust Hissing Sound. Once I Give It More Gas(pedal) The Noise Goes Away. Is This Normal?what Is This Noise?

 

Sounds like the exhaust backpressure valve is closing, it is normal if the oil temp is below 167*F but if you are fully warmed up and it is still occuring it could be the Exhaust backpressure sensor and tube are clogged.

 

No it is the exhaust passing by the turbine, not enough to speed it up but a little more fuel and it spools up the turbo and sound goes away

 

where is the exhaust backpressure sensor and tube that may be cogged located?and how do i uncogg this tube?

 

so this is normal and there is nothing wrong with my truck?

 

Does the truck kind of feel lagging, like its falling on its face, and then when the hissing noise goes away, does power come back?

 

the truck doesn't feel lagging but i can make the truck make the noise while driving in town and playing with the gas pedal just seems weird?

 

Hey guys, I just installed a 4" mbrp dual exhaust and my truck started making that hissing noise too. It is loud and very annoying. Like jraymond said, you can control it with the gas pedal. When I try to hold the pedal steady is when it starts hissing, If i push the pedal a little it stops and if I let off the pedal it stops. I find my self speeding up and slowing down just to keep it from hissing. Any help would be appreciated!

 

if it stops hissing after the truck gets to N.O.T it is the exhaust back pressure valve.(EBPV) it helps the truck warm up quicker..like amiller said it will stop when oil temp reads 167..if it keeps doing it after the truck has hit N.O.T the exhaust back presser sensor (EBPS) could be going bad or most likely the tube is full of soot..the little steel tube comes off of the passenger side manifold to the bottom of the EBPS just above and too the left of the water pump on top of the motor..take the tube off spray it with brake clean and run a wire down through it and check for cracks or holes in it...clean where it go's into the manifold and under the sensor as well..give it a try and report back to us..

 

my truck does the same thing when its cold its just the Exhaust back pressure valve closing to try and warm up the engine faster. Annoying, but nothing to worry about unless its doing this after the engine is fully warmer up.

 

my truck will do it even after its fully warmed up although the outside temp is very cold i'd say 0 to 10 degrees-i do know the warm up mode is working but it seems the backpressure valve is activating while i'm driving around town-like i said i can control it with the gas pedal-maybe i need to check the sensor or that tube? any help would be great

 

At those temps it can take a long time to warm almost 4 gallons of oil to over 167*. Even after the temp gauge reads N O T. Mine was doing the same thing when it was really cold out. Now that the temps have warmed up a bit around here its not doing it near as long.