When I turn off the engine, there is a hissing or 'pressure bleeding off' sound coming somewhere from the throttle body area. I know this is NOT the A/C bleeding off. Could it possibly be fuel pressure bleeding off? All is normal, but since I am new to the Wide Wonderful World of F-150's(But certainly not Ford's; have owned 10 in my life;especially muscle Mustangs, currently own a 71 Boss 351)I was wondering if I need to be concerned with this.
Thanx!!

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'97,4.6 x-cab,2WD,3:55 LS,4 speed auto.
Mods: K&N filter & Flowmaster.

 

I think this is normal. Mine does the same thing. I figured it was the exhaust air pump thing that pumps air to the cats? Or maybe the EGR valve. Never been too concerned. My '86 Mustang GT did a similar thing too.

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1997 F150 4x4 Off Road, SuperCab, Short Box, 5.4, Royal Blue/Silver, K&N, Gibson SS, LT265/75/16 Wild Country APT's

 

The first time I noticed this was AFTER I put in my superchip. Apparently I never had the hood open before and listened. I went crazy trying to find it. Had my head in the engine compartment with my wife starting and stopping the engine. Must have been funny from a distance
Its normal, I just hadn't heard it before.



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2001 Expedition 5.4L XLT
4WD + Towing Package
Edelbrock IAS
Superchip
Gibson SS Side Swept
Air Force One
Mobil 1

 

Mine does the same thing. Did it before I did any mods so I know the mods did not cause it. Might be the pressure going by the rings then out the egr or something.

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1997 XLT Teal 4.6L Flareside 4x4 ORP. Automatic, Reg. cab, 3.55LS, tinted windows, bug deflector, Dual exhaust, K&N Generation 2 air filter, BullDog keyless entry/remote start, Modern 16" wheels, bedliner, Covercraft tonneau cover, White faced gauges, electronic shift on the fly, Clarion ADX5655z Double Din Cassette & CD, 4 Pioneer TS-A6865 speakers and superchip, 01L headlights.

Future mods: Supercharger, headers, NOS, tranny upgrade(heavy duty gears, clutch packs, etc.), performance torque converter, composite driveshaft, bore cylinders 30 over, new pistons, crank, and rods, get performance heads or port the ones I have, 01 tail lights, 01 mirrors, 01 3rd brake light, gauges for the a-pillar, new L if they still make them and I like the way it looks, and a Z06 Vette or BMW Z3.




Click here to see more pictures

 

Could you have a Cobra engine? ;0

 

one of your old snakes got in the upper plenum...

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2001 Lightning, silver, escort 8500, ranger 2950dx dual band radio, wilson 2000 ant., bot/picked up on 05/08/01, 1997 f150 xlt 4.6L 4x2 with: a/f one fipk, superchip, optima battery, bbk 75mm throttle body, edelbrock ias shocks--2001 lightning to come(she came--see above)

 

Hi cjmf150

What you are hearing is the preasure in your
a/c equalizing, this is normal.
I work on refrigerators and they do it to
you just usualy don`t notice it.
IT`S NORMAL.

Have a good day.

Larry.

 

The hissing sound comes from the throttle body plenum throat. Take off the air inlet hose and you will see the butterfly. Dirt and goop gets built up on the walls of the throat. Especially when using a K&N filter and the oil mist gets on the walls and dirt clings to it. There will be a sticker there telling you not to clean the throat. BS. Use some WD-40 on a rag and wipe out the throat around the butterfly and do the edge of the butterfly where it closes against the throat. Problem solved. I posted this same question 3 years ago and all I got was "MY truck has big speakers and it's purple". Geez.

 

my truck does the same thing. i have no clue what it is but i know its not the a/c cuz my truck has no air conditioner

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1989 F-150 XLT Lariat: 2WD 302 5spd[*]Performance Accessories 3" Body Lift[*]33x12.50.15 BFG A/T's on 15x10 AR Rims[*]Rancho Steering Stabilizer[*]Rancho RS 5000 Shocks[*]K&N Air Filter[*]Gutted Cats with Straight Pipes For Now...

Go Full Speed or Go Home!

 

If we are not concerned with the noise should we bother cleaning this throat? Can any damage come from leaving it dirty?

Thanks
Jimmar

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2001.5 SuperCrew XLT 4X4 (Gen III)
Silver Clearcoat Metallic
Deep Wedgewood Blue (accent)
5.4L V8
Chrome Tubular Step Bars (Ford)
Captains Chairs
Power Moonroof
3.55 LS
6750 GVWR
Class III Towing Pkg

Mods:
Harley Davidson Exhaust
'01 Lightning Head/Tail Lamps
Pioneer DEH-9200r
Boston Acoustic Components & 5X7s
Box Liner (Ford)
Splashguards (Ford)
Bug Defector Doubles as Rock and Sand/Salt Deflector in these snowy Canadian winters
K&N Air Filter

To Come:
17" Rims/Tires w/ BFG A/T or ProComps
WMS Velocity Tube
Radio Delay Mod
Eurolights