I have a 350 tbi that i will be swapping to tpi in the next couple months. In the mean time i have a walbro 255 pump for when the time comes. Next week i am having a rear put in my car and was wondering if i should put the pump in then while the tank is down. Will the pump pump too much or will it be okay for a few months?

 

I'm running a granatelli 255lph pump in my tbi setup. I'm also running stock fuel pressure (9-13psi). My regulator seems to bleed off the excess fuel and return line appears to handle the excess flow just fine.

I also didn't think dropping the tank was that big of a job. I'd do it again if I had to.

If you do decide to swap the pump now, just be sure your fuel pressure stays within the same range you have now. If it is raised your car will become universally rich and if it is lower it will lean out.

just my 2cnts based on my experiences.

good luck

 

I was under the impression that if the fuel pressure at the port before going to the TB was higher than 13lbs that the regulator in the TB would keep it at 13lbs to the injectors and bypass back to the fuel tank. Am I wrong? Wouldn't that shoot the hell out of the fuel pressure regulator adjustments mentioned in the ultimate TBI mod's?

 

I believe you are right on about the pressure regulator operation.

The regulator will maintain a certain pressure on the fuel supply line. The supply line consists of all components from the pump to the injectors. If pressure on the fuel supply side is higher than the regulator spring pressure the bypass valve will open allowing fuel to bypass back to the tank via the return line.

I don't believe that the increase in fuel volume would affect the adjustability of the AFPR described in the UTBI Mods. Granted I haven't made the AFPR mods described in the UTBI mods. However, all the UTBI mods calls for is the replacement of the fixed spring cup with an adjustable one. Since the regulator only regulates pressure and not volume, as long as the volume of fuel being bypassed back to the fuel tank does not exceed the max allowable flow through the bypass port in the regulator the pressure shouldn't change. You'll just send more fuel back to the tank.

With my stock pump I measured 11psi on the supply line before the TB, and after I swapped in the new 255lph pump I measured 11psi again.

Again, I am basing the above on my understanding and experiences with my car.

 

I wonder what pressure the TB regulator is set from the factory? I've read that it wasn't too consistant (+- 1 lb ). I recently replaced my pump with an aftermarket factory replacement. The pressure before was 7lbs and after it was 13.5lbs. Seems like your pump would be putting out more than mine. 49 bucks at Napa and it wasn't no walbro. But, that was at idle! Your's might deliver more pressure at WOT than mine because of it's capacity
to deliver more volume on demand.

 

Stock speck IIRC is 9-13 psi, so the range is more than +/-1 psi. Sounds like you had a bad pump if replacement jumped from 7 to 13.5. And there is nothing wrong with the stock Delco pumps if you want stock pressures, they just won't go higher. Based on mine and what I read, current Delco pumps won't go over about 15 psi without dead-heading (no flow and won't last), though I'm told the older ones could sustain pressures up to 16-18.

 

That's one point I forgot in the last post! I believe that I'm having a pressure issue at high RPM as my engine wants to cut out at between 4500 and 5000 and it feels like fuel starvation. Either that or probably a combination of old cam, lifters and valve springs. It does have 145xxx on it! I guess I'll just have to keep it under 4500 till I figure out what I want to do, rebuild or replace.