wano1147

I have a fuel supply problem with my 383 sbc in my 1988 Formula.(was a TBI car) I have installed a custom MPI system controlled by a MS1 ECM.
I can'tseem to get enough fuel to the motor, the intank fuel pump just supplys fuel to the high pressure inline pump but it was losing pressure (down to zero)at about 5000 rpm and about 3/4 throttle. I replaced the inline pump (45 gph) with a larger (63gph) pump and that helped but pressure still drops to about 30 psi. I was wondering if it would help to run power directly from the battery or alternator to the in tank fuel pump (leaving in the oil pressure switch) to make sure the pump has all the voltage and amps it requires to run at full capacity? Do I need a relay to do this? Or would a larger flow rate fuel filter help?
This motor is probably capable of HP in the 450 range, running 29 pph injectors.
Anyone else run into this problem?

pizza_guy

From what I gather, you still have the stock TBI pump in the tank? That's just a recipie for disaster, seriously. EFI fuel pumps are not meant to "suck" gas at all. Your stock pump is the restriction, because your new pump can't "suck" gas through it. A TBI pump WILL NOT EVER flow enough gas to support 400+ HP. Probably not even 300 HP. I want to rant at you for pages about that setup, but I think you get my point.

Unless your stock wiring is corroded, running a wire from the alternator will make zero difference.

Do it right. Pull the tank, put a walboro IN the tank where it belongs and be done with it. My very first time pulling a gas tank took me all of 4 hours.

Shortcuts only lead to engine death. They can also lead to PERSONAL DEATH if you shortcut your fuel delivery system.

You know what happens when the fire department finds a car on fire?? They spray the area around it and let the car burn itself out. Imagine standing there, fireman standing next to you with a hose, and watching your car burn to the ground in front of you...if your lucky enough to escape.

wano1147

pizza guy,
Thanks for your reply, I had no intention originally to use the TBI pump. This system started out as an Edelbrock MPI conversion kit that I modified with 29 pph injectors and a big block TBI throttle body, I installed the pump that came with the system (new pump in box, correct part number) but it only made about 12 psi. I don't know the reason for this. I thought an inline pump might keep me from pulling the tank again. What is a walboro? Is that a brand or type of pump?

pizza_guy

Yeah, a Walboro is just a brand of pump. If you search around here, they are generally the brand people like the most. If you buy a holley or edelbrock, it's essentially a Walboro, just overpriced and reboxed. The Walboro 255 pump is the cream of the crop as far as in-tank efi pumps are concerned.

It sucks, but there really is no way around pulling the gas tank to install a good fuel pump.

And, after reading my earlier rant, I didn't mean to sound so preachy. I just want people to realize that they are taking their life in their own hands when they customize their fuel delivery system. I've seen 45psi setups with plain rubber hose and hose clamps!!! Might as well play russian roulette every time you start the car.

I don't want anybody blowing up their car/themselves just to go fast.

wano1147

Just to follow up in case anyone has similar issues.
I installed a product called V-Plus from Caspers Electronics that boosts the voltage about 2 volts on the vehicles entire electrical system. This is triggered by the TPS at 70% throttle. This voltage boost increases fuel pump output and also gives the ignition system a hotter spark when you need it most.
The fuel pressure no longer drops at high revs and the injectors run at a max duty cycle of 85 percent.
If anyone is interested you can look at casperselectronics.com