My 88 IROC 5.7 has the following mods: free flow cat, flowmaster muffler, Hypertech chip, tpis airfoil, k/n airfilters, pocket ported heads, zz-3 cam, accel 8.8 wires, and flow improved maf.

The problem is the car runs fine at idle and for the first 100yds or so then it just falls flat until you let of the gas at which time it will roughly idle. The computer set a code 33 and 36. I replaced the maf and it changed nothing code 33 was back immediately. The car hasn't been driven far enough to be able to tell if the code 36 comes back. Fuel pressure at idle is 39 psi when the throttle is applied it raised to 45. When I unhook the regulator and block of the vacuum tube pressure raises to 45 and the car will now run. When you turn the key on with the engine off fuel pressure shoots up to 45 and then falls quickly to 0. When opening the gas cap air can be heard entering the tank because of a strong vacuum. After along drive if you park the car you can hear the tank actually pop back out. The car also will not keep from popping the 3 amp crank fuse. I haven't checked what effect removing the gas cap and releasing the vacuum has on fuel pressure if any but will do so tomorrow.

Any help on this will be greatly appreciated.
Thanks in advance,
Jason

 

I checked the fuel pressure with the cap on and off there was no change.

With the vacuum unhooked and plugged off on the regulator the car ran better than it ever had for about two miles then it fell on it's face. When the car is messing up the fuel pressure stayed at a constant 46psi

 

Can you monitor fuel pressure while you are driving? (pardon me if you have already done so.....)

 

I did check the pressure while driving and it stays constant.