vacuum leak?

i've got a 91 Caprice (duh) LO5 (5.7L TBI). Very poor performance under load, stalling and very rough idle when still and its impossible to keep it running with the A/C on.

I've noticed a new hissing sound (vacuum leak) and cannot determine it's origin. Vacuum at TBI is healthy, couldnt get a reading at intake manifold (0 inches of mercury when tested warm regardless of engine speed).

I know I have a hole in my fuel tank preventing it from building pressure. Is this part of my problem? any input about the vacuum?

I don't know about the vacuum leak, but it probably would be good idea to replace your tank if it has a hole in it. Gasoline vapors are harmful and there is a potential for a fire/explosion. The hole is also probably reducing your fuel efficiency and may affect the fuel pressure if the level in the tank gets too low.

Spray some TB cleaner around the base of the TBI especially in the rear. If the idle changes, the TBI gasket is bad.

Also check the bolts on the intake manifold are tight.

//2000CAYukon

problem solved folks. turned out the noise i was hearing was a long crack along the inside seam of my old+clogged catalytic converter