"whistle" on decel

ezernut9mm · Post by **ezernut9mm** » February 5, 2011, 12:37 am

any ideas? only heard it this winter. let off the gas and get a sound kinda like the air being let out of a balloon, step on the gas and it goes away.
truck runs pretty cold. i wonder if it's cooling system related? kinda hard to diagnose while driving and is non existent while idling or revving at a stop.
definitely not mechanical (gears, trans, etc).
i am stumped.

3ontree66 · Post by **3ontree66** » February 5, 2011, 1:49 am

Sounds like you got the very rare Turbo Diesel 61 Ford Uni. Or, someone strapped one of those gangster Whistles to your exhaust.

Does one of your tires keep going flat??
Did a PO install a deer warning device on the truck?

That's it, my mechanical arsenal!! I'm Stumped!!

F7BIGJOB · Post by **F7BIGJOB** » February 5, 2011, 5:34 am

Chris, vacuum leak at/ under/ around carb.? Does it go away afta ithe engine warms up?

BarnieTrk · Post by **BarnieTrk** » February 5, 2011, 8:51 am

HAHAHAHAha...3ontree66, I about spit out my coffee, Dude! Too Funny!

I'm with the BIGJOB on this... and I'd also run my hand also each of your vacuum lines for cracks or burned/rubbed holes and loose hose connections, etc.

BarnieTrk

slick4x4 · Post by **slick4x4** » February 5, 2011, 9:30 am

sounds like a vacuum leak for sure...
here is a good (and fairly safe) method to find a vacuum leak
get a small torch = little bottle propane hand held torch
turn it on, but dont light it
while your engine is running you can put it up to your vac lines /carb plate /ect
if it gets close to your leak , the engine will change RPM
be careful of course, and if you do this in garage, door probably should be open

MadMaxetc · Post by **MadMaxetc** » February 5, 2011, 9:46 am

slick4x4 wrote:sounds like a vacuum leak for sure...
here is a good (and fairly safe) method to find a vacuum leak
get a small torch = little bottle propane hand held torch
turn it on, but dont light it
while your engine is running you can put it up to your vac lines /carb plate /ect
if it gets close to your leak , the engine will change RPM
be careful of course, and if you do this in garage, door probably should be open

x2

MadMaxetc · Post by **MadMaxetc** » February 5, 2011, 9:47 am

Check all the little rubber caps on the carb. I had a Holley that did the same thing.

Astrowing · Post by **Astrowing** » February 5, 2011, 9:47 am

Mine is doing to same thing, and performance seems to be fine although it is definitely running cool also. I've noticed that the Holley 1bbl on the 223 has an externally mounted economizer valve, which looks like to me it could make vacuum noise if it is leaking. It looks just like a power valve on the 2bbl and 4 bbl carbs. I'm rebuilding the carb as soon as it gets warmer and we'll see what happens.

ezernut9mm · Post by **ezernut9mm** » February 5, 2011, 9:09 pm

my carb has been rebuilt although i guess the eco valve could be bad. i am almost thinking bad radiator cap although that is just a guess.
it seems like it starts after the engine is "warm" and i have been on the highway. like it is building pressure or something.
i don't see it being a vacuum leak as there is only the advance line and it is steel. i have checked both connections. there are no rubber caps anywhere.
i will investigate more tomorrow.
how do i tell if the radiator cap is bad?

slick4x4 · Post by **slick4x4** » February 5, 2011, 9:15 pm

if the rad cap was bad , it would probably slobber some antifreeze out
does it run good ? ... the choke isnt partly closed is it ?

ezernut9mm · Post by **ezernut9mm** » February 5, 2011, 9:20 pm

choke is wide open, runs as good as it should (with a carb rebuilt by me), and doesn't slobber any coolant.
i was also thinking that with it running so cold that the t-stat might be stuck open or something. right now i am just throwing rocks in the dark hoping to hit something.
also, it does not sound like vacuum. it sounds like pressure, but it doesn't puke any coolant so i don't know.

Lowell · Post by **Lowell** » February 5, 2011, 10:50 pm

Once had a whistle on a car owed by a dealer i worked for. turned out to be the intake manifold leaking vacuum. It stopped after I tightened the bolts.

pugsly · Post by **pugsly** » February 5, 2011, 10:51 pm

If you have a pcv valve, remove it and plug the line, then retest. I have seen this many times. Just a possibility.

ezernut9mm · Post by **ezernut9mm** » February 5, 2011, 10:55 pm

no pcv, road draft tube.
thanks for the replies so far guys.

samdog1966 · Post by **samdog1966** » February 5, 2011, 11:26 pm

If it whistles or hums it probably dosen't know the words.

ezernut9mm · Post by **ezernut9mm** » February 5, 2011, 11:28 pm

lol. thanks john.

F7BIGJOB · Post by **F7BIGJOB** » February 6, 2011, 3:55 pm

Chris, do you have a heat riser valve on the exaust? [don't remember if you have a 6 or 8] Just thought it may be sticking when you had mentioned 'pressure' sound.

ezernut9mm · Post by **ezernut9mm** » February 6, 2011, 9:56 pm

yes it does and it appears to operating properly. i replaced the t-stat and radiator cap today, but didn't road test it. there are other issues that i will bring up in a new thread. they may be related.

Astrowing · Post by **Astrowing** » February 8, 2011, 9:39 pm

I took my carb apart tonight and my throttle shaft is loose. I don't know what the specs are, but that could cause a vacuum leak depending on throttle position. Could be your issue also and it probably is worse in cold weather because of the increased tolerances between the parts. I'm investigating what the Holley 1904 specs are. This was the only obvious issue I found.

ezernut9mm · Post by **ezernut9mm** » February 8, 2011, 10:03 pm

cool. let me know. mine didn't seem loose, but that doesn't mean anything. i am actually thinking about replacing it with a carter or autolite.