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

 

You should have better luck here but this may need to be moved to the carb section.

 

I already have it there, as well as the TBI section.

I figure if I put it in the three areas, someone should know how to get this striaghtened out.

 

Well, it's not hard to rewire the pump yourself. I'd buy a cheap 30-40 amp relay at one of the chain autoparts places, some good 12 gauge wire and connectors and wire it up myself to be on when the ignition is on. There is currently a single hot wire running to it from the relay on the firewall, you can use that or run a new wire on back closer to the pump and splice in as I did. The wire runs through the floor right behind the rear passenger seat, you can fold down the seats and pull up the carpet and get it at. I spliced in right there. You'll have to check with a wiring diagram for your year for the color wire, I've forgotten what it was anyway. I did that with my intank TPI pump for awhile. But I don't think the computer can actually control the voltage going to the pump and thus it's output. Unless I'm mistaken all the computer has to do with the pump is whether or not to operate the relay to power it all, I don't think it can control the voltage.

The regulator needs to be a return style like the Mallory regulator was with the return line hooked up properly. If this new regulator is not a return type it will be hard on the pump. As to the fluctuations, what exactly do you mean? You mean you set it at 5 or whatever but it jumps up to 8+ and stays there? The needle on my pressure gauge always jumped around a bit quickly, like the best I could do was set it to a range of 5-7 psi. But even 8 psi really should not be flooding it I wouldn't have thought. My TPI pump died not too long ago (after a couple years of running my carb setup). My new mechanical carb pump runs an indicated 8-9 psi with no regulator (I put my mallory back on and dialed it down to 5-6 though...).

Anyway, I'm not sure exactly what is causing your problem, but you should be able to wire the pump up more directly without much trouble just to eliminate it from worry. It wouldn't surprise me if the Mallory regulator was causing the problems, I've never really liked the way mine "flickers" the psi for lack of a better term, but once I had mine set it never went any higher either... But if the new regulator you got isn't a return style I don't think that is going to work well either, likely kill the pump early...

Best thing to do if you continue to have problems is just to pull the EFI pump, install a pickup in it's place (I just used a 6-8 inch section of rubber fuel line hose in it's place for mine or you could swap over to the whole pickup assembly from a older carbed 3rdgen) and run a more traditional mechanical pump... You definitely should not have put a high pressure EFI pump back in place when you swapped it out recently, that was the time to do it right...

 

I'd suggest using the stock relay; cut the 2 coil wires (small gauge wire) back a foot or so from the relay; ground one of them coil leads, and hook the other to a source of switched ignition; and leave the wires from the battery to the relay, and the relay to the pump, exactly as they are. Minimally invasive, the least chance of having bad connections, intermittents, etc.

 

The fuel pressure is constant, and it does not flicker at the gauge.

I will set the regulator so that the gauge reads 5 psi, then after driving it may shoot up to 7 or 8 psi and stay constant, then it may go back to 5 or even 4 psi. This happens a lot if I set the pressure, then shut it down, and then restart it. Upon restart I have a different fuel pressure than I left it set at last time.