Here is the deal, read carefully: I have a 1991 RS, used to have the infamous L03 in it. Ever since I carbed it, I have always had a problem with the fuel pressure spiking. In other words I would set it to 5 PSI and then the next time I start it up, it shoots up to 8 PSI and the car runs like poop. I know the gauge was not faulty at the time, because it would begin to run rich, as in I could smell it, and the A/F gauge would read significantly higher. NOW: I just swapped the L03 for a built 355. The carb is the same, a Road Demon 625 cfm (not the new crappy ones, the one with the center hung floats). I pulled the old fuel pump out and installed a Holley 255 gph ( or Lph, can't remember) to accomodate the new motor. Now the fuel pressure was set to 5 PSI and my Dad was backing the car out of the shop to check the trans to make sure it was shifting and all that, and all the sudden it starts running like a rolling fire starter. The motor flooded so they shut her down real quick. I have a Mallory 3 port regulator in the setup, stock fuel lines, stock gas tank, a single fuel pressure gauge on the carb feed fuel line. I left the computer hooked up so other things would function, and I know that the fuel pump is partially controlled by the computer, I think it is actually my problem. The computer is going haywire cause none of the sensors are hooked up and it's sending spikes in the voltage to the fuel pump. The mechanic working on my car seems to think that I cannot run an EFI/in-tank fuel pump with this setup cause it is going to give me too much pressure. I do not agree with that, I know that many of you are running this kind of setup, with that fuel pump, and a carb. What do I do? How can I run the fuel pump with a constant voltage??? When I look at the wiring diagrams there are many other things connected to the hot lead that goes to the fuel pump from the computer. I don't really want to mess with that. Is the in-tank fuel pump the actual problem?? Could some of the seals on my Mallory Regulator be shot already??? Today my mechanic installed a 2 port regulator on the carb feed line and he has the pressure down where it needs to be again, however I don't know if it will stay there, and if it won't remain constant, it's impossible to tune the carb correctly. Please give me some suggestions, Thanks in advance, and sorry for the super long post. Matt

SOunds like your fuel regulator. It should hold the pressure to whatever you specify regardless of what the pump is doing (unless it doesn't work.)

I would go get another one.

One more thing before you do that. It might be possible that your return line is clogged. If that were the case however you wouldn't have any return and the full 85psi would be going to your carb, so my bet is on the regulator.

Tom