So when I've starting my 89 d100 lately there has been some extra noise comiming from under the hood. It sounds to me like it might be a vacuum leak but I can't seem to find one anywhere. Are there any hidden vac hoses that I'm just not seeing?


When I step on the gas the sound gets louder, and seems to last quite a long time. Also could the downstream air line be making this high pitched noise??? Thanks all

 

With the engine running,carefully try to find the general location of the leak by ear,then use carb cleaner or ether and spray one area at a time and listen for a change in rpms then narrow your spraying to exact spots till you find it.

 

my truck had a loud, pulsating air type of sound, that got louder as the rpm's went up. after some investigation, it turned out to be the air pump. the previous owners plugged the air tube underneath the truck, presumably when it rusted off the cat. here in PA, we have to have all that emissions stuff, so im working on replacing all of it now

 

Lmao my air tube isn't connected to my cat it's just hanging there. Which is why I asked.... Also it's bent at a 90deg. So it points straight off to the passenger side of the truck. Can this be straightened back out? If not where can I get like a foot of the hard metal end? I really need it to be connected to something