2005 T7500 gmc truck

[adamsproduce]

Hello i have a gmc 2005 t7500 truck. I am having some type of issue when releasing the gas pedal the engine doesnt make make that brake air type noise when coming to a stop. It rolls like a car with no noise and sometimes it will have an air build up and make that engine slowing down noise. I do not have air brakes. Also when picking up off a red light it makes that a normal truck sound and gets quiet with a zzzzz sound.. Exhaust light on dashboard also goes off when warming truck up? any answers will be helpful thanks

[Diaric]

moved to medium duty trucks

[sh8kr]

Diesel? Exhaust brake? More info please the more you include about the truck the easier and most accurate help can be answered.
my 2$
Steve C

[adamsproduce]

hey sh8kr i dont have much experience with trucks but i am trying to understand whats the issue on the truck. ill try to give you all the info i can.. well its a gmc T7500 2005 caterpiller engine boxed truck... i have an exhaust button on the dashboard but i dont use it because i need to purchase a new air compressor that works with the air seat and exhaust brake. what my truck is doing is this when driving on the highway i hear a fluctuating air engine noise going up and down up and down. its not a hissing air noise its like an engine howl noise... also when approaching a stop there is no sound of the truck helping me to stop which i think is part of the exhaust yielding . hope i didnt confuse you.. i will take my truck to a mechanic but i just wanted to know what i might be looking at so he doesn't push me other things..
the thing is when i drive and come to a stop as rpm are lowering it makes that engine lowering sound and most of the time it doesn't do it like an on and off thing.. maybe its the engine fan or something in the exhaust flat that is not opening.
thanks for your time bud..

[heymccall]

No compressor = no engine brake. Simple 'nuff.

You need the compressor.

[Diaric]

sounds like an air to air leak

[adamsproduce]

even when i had the compressor it was the same. i dont use the exhaust button but with it being off when u let go out the gas pedal as the rpms go down the engine has that lowering sound. that sound comes and goes and it sounds like something is like chocking it.. its weird. ill have to have a mechanic take a look at it..

[heymccall]

Most actuate the engine brake feature with a proximity switch integral to the low idle adjust screw. The throttle lever must touch the adjuster screw (has two wires). IF you elevate the engine speed at all, with the manual throttle knob, the throttle lever will NOT touch the low idle screw/ switch.
Many Cats have a double throttle spring there, too. They are a spring within a spring. Kinda important, too.

[adamsproduce]

Originally Posted by heymccall

Most actuate the engine brake feature with a proximity switch integral to the low idle adjust screw. The throttle lever must touch the adjuster screw (has two wires). IF you elevate the engine speed at all, with the manual throttle knob, the throttle lever will NOT touch the low idle screw/ switch.
Many Cats have a double throttle spring there, too. They are a spring within a spring. Kinda important, too.

hey. well i dont have much experience with trucks so my best bet would be to take it to a mechanic and try to explain it to him.. my truck doesn't have an idle knob but a button on the dash there is a button that raises the idle up a bit.. are you saying that this can be causes by a low idle ? i do think my truck needs to have its idle raised as it is because on a morning start up it shakes.. thanks for your help bud

[adamsproduce]

hello, so my truck is at the mechanic right now. ive been having a new issue which is this. when i start the truck up the engine shakes like crazy and chocking with white smoke and if you hit the gas a bit there is no response. i would life the cabin up and push multiple times on the fuel pump until it clears out and right away give a bit of gas to keep it running other wise it would shake on idle and smoke badly. i would also get stuck on red lights where your about to hit the gas and it starts shaking smoking and no movement. mechanic is telling me its a transmission control or something like that. does that sound right, and is that part expensive ?? someone please let me know.. thanks