2 fuel pumps on an efi?

[cbautoworks1]

trying to figure out why i have 2 fuel pumps. the previous owner had an air density system and i am changing it to the mass air with an a9L computer. he had told me the 1st pump by the tank was a low pressure pump and the one in the engine comp. was a high pressure. my question is do i need 2 pumps? if not can someone tell me what setup i need. fuel line size and pump size. thanks! really lost!

 

[70_Steve]

Lots of discussion and debate on our FI fuel systems. There's the low pressure pump feeding an accumulator with the high pressure pump pulling from the accumulator. Then, like what your system sounds like, there's the low pressure pump piped straight into the high pressure pump. Then there's the plain old high pressure pump, which can be mounted either in the tank or external to the tank.

I don't know if anyone has agreed on what's the "best' system for our vehicles, or even a "best" system for a particular vehicles application (rock crawler, mall crawler, dune runner, etc).

Given all the discussion and debate, and given that I have a 23 gallon tank that does not have the provision for an in-tank pump, I decided to stay with the KISS principal. I currently have installed one single E2000 high pressure pump. It's installed pretty near the tank, since the high pressure pumps don't suck all that well. So far, the little bit that I've driven it on the street, it's done it's job. If I run into issues, then I may consider adding other "stuff".

 

[trailpsycho]

IF its working, dont change anything. I am also running the same setup, a high volume Carter 4070 puller pump to feed my E2000 HP (pusher pump). Almost 25K miles and no problems (from the pumps) to date. Make sure there is a filter between the tank and the low pressure pump and another high-filtration filter between the low and high pressure pump.

There is really no reason to change anything, add anything or remove anything, if it is working for you as it sits now. The mass air computer could care less if it turns on one pump or two...just like the SD ECU, it only sends a signal to the relay to run the pump(s). The key thing is to have a low pressure pump that outflows the HP pump.

Have fun... and Good luck.

 

[Broncobowsher]

The early for EFI was using old design fuel tanks that were fine for carburated use but not so good with EFI. Difference is with a carb you can accept a momentary loss of fuel at the picup point as the carb will keep running just fine on what is in the fuel bowl. But EFI cannot accept a momentary drop in fuel delivery. The cure was 2 pumps and an accumulater.

If you look at just about any late 80's ford EFI truck you will have 2 pumps. And this little thing about half the size of a soup can between them. That little thing is an accumulator to keep a steady supply of fuel to the high pressure pump even if the pickup from the delivery tank gulps a little air. Later trucks got better engineered fuel systems in the tank and removed the cost and complexity of the second pump.

The 2 pumps is a copy of the original fuel system but often neglecting the accumulator. then there is the high pressure pumps don't like to suck fuel. It has been a blanket clause forever and isn't true. What is correct is "some high pressure pumps don't like to suck fuel", mainly centrifical style pumps. That style needs to be feed and acts like a booster pump more then a delivery pump.

Did that just stir the pot of muddy water?

 

[jedblake]

Good post broncobowsher! Now I know where BC Broncos came up with their set-up for the carbed fuel tanks.

 

[cbautoworks1]

thanks guys. sounds like i should just let it roll like i have it. that said, any idea on how to check my sending unit in the tank so i know which fuel guage to by. it looks like i have the original rear tank (no front tank).