drewsky121

Alright guys, here is a new one.
Had an explorer intake on it, and i found a crack straight through the port and it was causing vacuum issues, obviously. So, as every good car guy would do, i upgraded to an edelbrock RPM II intake. i cleaned everything as always on the head side, and sealed up the lower intake manifold like i have with over 100 others. not exaggerating, so figured it was all good. threw the upper on made sure that was good, all fittings tight with teflon, all hoses plugged in. go to start it up, and there is no vacuum. i have no brakes, my vacuum gauge is barely reading at all, and even my MAP sensor is showing about 95 kPa (.93 atm, 13.7 Psi) and its barely running, once again, obviously. I've chased it down with carb cleaner and i can't find a single source of vacuum loss on the top side of the motor. throttle body is tight, all fittings are tight, PCV is in and tight, gasket on the lower side of the plenum is tight and sealed, upper to lower is sealed, and i couldn't find a leak from the lower intake to the cylinder head.... little confused on this one.
any suggestions?

dawson1112

Base Idle reset? What is it idling at while its running ?

Did you get the dizzy stabbed back in correctly?

Just a few things that come to mine.

drewsky121

yup, first thing i checked. reset dizzy, it was fine and right on. it idles at whatever i can get it to idle at right the, mainly around 1200 and waves and dies eventually... all obvious signs of a vacuum leak but can't find it.

dawson1112

Blow some smoke in the system some how.

I seen someone on here the other day explain how to make your own smoke vacuum detector using some compressed air a tin can and a smoke bomb lol ....

deputycrawford

The trick I learned years ago is to grab your small propane torch. Then the fuel on but don't light it. Run it around the area you think you have the problem, but go very slowly. When the propane finds the vacuum leak the engine will use the propane and rev slightly. You have found your vacuum leak and don't have all the stains from the carb cleaner. Good luck.

Jerry

petrock

Yeah, but you run the very high risk of fire/explosion by using propane.

The vacuum to your brake booster comes from the intake manifold. Follow the hose from the brake booster back to the intake and see if you find any cracks or brakes. Bend the hose a little to help reveal them. If you don’t find any, pull the vacuum hose at the intake manifold and see if there is any vacuum there. If not, then the problem is between the intake manifold and the combustion chamber.