I purchased my F350 last April. 2 weeks after owning it I was impressing some girls and I took a road unknown to me. The road has a hill that is more like a ramp. Anything over 45 mph and your stomach flips. On full compression of the shocks (wheels did NOT leave the pavement), the turbo started hissing like it blew it's housing off. I talked to the local repair shop and they said the turbo and/or the wastegate are bad (I didn't mention the "jump"). I was never able to replicate the sound when I was at the auto shop, which is irritating but predictable. A week later, the sound went away, coinciding with the weather getting much warmer. This week the weather dropped down to the 40s and the noise is back. It usually happens right at the point where the engine and vehicle speed are balanced, between acceleration and deceleration. Anyone ever have something like this happen?

 

Thread moved

 

MY 2000 350 DOES THE SAME THING. I NOTICE MORE AT LOW SPEEDS WITH THE WINDOWS DOWN REGARDLESS OF TEMP. MINE TOO IS A 6sp., AND I CAN MAKE IT HAPPEN AT WILL IN THIRD GEAR. I HAD SOMEONE TELL ME IT WAS RESTRICTIVE EXHAUST BUT THAT WASN'T FROM A RELIABLE SOURCE. I'M SURE SOMEONE ON FTE WILL HAVE AN ANSWER.

IT MAY BE TOATALY UN-RELATED BUT I HEAR PSD'S ALL THE TIME (ESPECIALY VANS) DRIVING BY WITH THAT HISSSSSSSSS.

 

Probably your exhaust back pressure valve.
Or your turbo was simply stalling under the heavy load. The 99-03 models have an intake wheel that tends to make a sound similar to a flag flapping in a hurricane under very heavy load.
Also when you are really working the motor like that and you suddenly back out of the throttle you'll get a woosh sound of all the boost pressure blowing back out of the intake.

 

It happens under load or empty. It seems to be that heavy throttle makes the hiss get louder and then go away much more quickly then just mild throttle and it does appear to focus on third gear.

I'll research the exhaust back pressure valve. If I were to install an exhaust brake, would this replace the valve and possibly end my problems while at the same time adding a cool, new toy?

I'm still learning about these trucks so I'm glad you guys are around.

PS. Thanks for moving the thread.

 

Did you check your FoMoCo Anti-hiss valve?

 

Since you have a six-speed stick and want an exhaust brake, this will give you an effective exhaust brake for about $15.00.
https://www.ford-trucks.com/forums/s...d.php?t=268610