Tried finding vacuum leak, now cruise control doesn't work.

[6 Nebraska IDIs]

The cruise systems on these trucks gets more complicated the later in production you go. I was having issues with my brown truck not maintaining speed or taking a long time to pick up and hold speed. I knew I had a vacuum leak because I have stiff brakes. Well while trying to find the vacuum leak by pressurizing the vacuum system with 4-5psi or air pressure it appears I damaged something. Cruise no longer works at all now. I have a spare cruise transducer so I'm installing that today.
I need some better advice on how to find this stupid vacuum leak though. I can hear it hissing after I shut the truck off so I know its there.

 

[Dsl_Dog_Treat]

Coffee can mount?
rust likes to creep in around there first.

 

[riotwarrior]

I dunno...as it's not a running vacuum from the manifold...it's a tough one, I'd think soapy water and when that stops the hiss or changes the tone you hit the leak????

Or some type of fluid...

Clearly the old PROPANE over vacuum lines like on a vehicle with a gas engine won't work since our vacuum does not enter the engine! DOH!

opcor

 

[icanfixall]

That vacuum resivour on the drivers side of the engine bay does rot out on the bottom. Mine did many years ago. Some rtv sealed it up fine... Never had anymore issues either. Sounds like you opened up a bigger hole somewhere too with the air pressure. If the leak is still hard to find just remove one vacuum line at a time from the manifold on the firewall and pressureize it. then spray it with soaky water till you find the leak.

 

[franklin2]

The way to troubleshoot the problem is to isolate the different lines. You say you can hear it, but it would be even better to tee a vacuum guage in the main line to the pump. Then just start unplugging lines and putting your thumb over them till you see a big jump in the reading. Or you could just unplug the lines at different places till you cannot hear the hissing noise.