Got a propane torch? Don't need massive quantities of propane to find the leak, and it's a hell of a lot safer than liquids. I keep beating this dead horse, so that I don't wind up with dead or homeless friends on these forums. Liquid solvents on a hot running engine are a very BAD idea. The propane torch won't put out enough gas to get dangerous. Stink, yeah, but blow up, no. With the nozzle, you can reach under the plenum curl quite nicely, and point the gas EXACTLY where you want it to go.
Is this a 5.0 or 5.8? If a 5.0, they're prone to plenum/intake gasket failures. Takes about 30 minutes to have the intake off the truck, ready to clean. I even pulled my injectors to check them for debris in the screens, and put new O's on them. Good time to CLEAN the throttle body and IAC the right way. Won't hurt to soak the plenum in Seafoam if there's some crud in it too. Just re-gasket the whole top end. After you get it back together, leave everything except the MAP and FPR disconnected, and cap off the nipples. Hook up the vac gauge on the nipple for the EVAP cannister, and check it again.
Should be something close to 20 inches vacuum. Start hooking the hoses back up, one by one. If the vacuum drops after connecting a hose, you just found the source of the leak. Sometimes, a tiny leak in the EGR will squeal VERY loudly, albeit a tiny leak. The shaft seal in mine is worn enough it squeals, especially on a cold engine, but doesn't warrant replacement yet.
Is this a 5.0 or 5.8? If a 5.0, they're prone to plenum/intake gasket failures. Takes about 30 minutes to have the intake off the truck, ready to clean. I even pulled my injectors to check them for debris in the screens, and put new O's on them. Good time to CLEAN the throttle body and IAC the right way. Won't hurt to soak the plenum in Seafoam if there's some crud in it too. Just re-gasket the whole top end. After you get it back together, leave everything except the MAP and FPR disconnected, and cap off the nipples. Hook up the vac gauge on the nipple for the EVAP cannister, and check it again.
Should be something close to 20 inches vacuum. Start hooking the hoses back up, one by one. If the vacuum drops after connecting a hose, you just found the source of the leak. Sometimes, a tiny leak in the EGR will squeal VERY loudly, albeit a tiny leak. The shaft seal in mine is worn enough it squeals, especially on a cold engine, but doesn't warrant replacement yet.