I have made a double pumper fuel system with E85 Walbro F10000302 (240L/min 3bar) + Walbro 450 (267). The smaller pump runs an6 from pump housing to stock fuel line to an6+an6 to An8 y-fitting and the larger pump runs an6 fuel line to y-fitting. The y-fittnig is connectd to Bosch fillter and there is an8 line between the filter and aem fuel rail . And the return is stock. The smaller pump is wired to stock (low/high) wiring and the larger pump is hardwired and kicks on about in 10-12psi.

The system runs fine on cruising. The smaller pump works fine and doesn't overflow the return line even on high voltage mode. But when I do a full 3rd gear pull (and the larger pump kicks on) everything is fine until I lift the gas pedal -> the fuel pressure drops to 0 and the engine stops. The smaller pump doesn't have a check valve, so I installed one between the smaller pump and y-fitting. It didn't help. And if I run only the walbro450 (stock wiring+ hardwired with hobbs switch) it works fine and keeps the fuel pressure over 2 bar after a 3rd gear pull. But it overflows the return line on cruising on high voltage mode. And I am worried, if the stock wiring can handle the amps when cruising a long period with stock high voltage mode.

So it looks like, the smaller pump just can't make enough pressure after the 450 stops working. I was thinking of replacing the smaller pump with bigger one. Has anyone build a good working small+big pump double pumper?

 

doesnt make any sense how it could go to 0 psi when the big pump turns off.

unless somehow its back flowing through the big pump somehow

 

Almost sounds to me like the check valve in the big pump isn't closing.

 

The problem are not the pumps themselves, but for some reason there is an electrical surge created when the 450 kicks in, followed by an electrical drainage/shorting that affects the oem fuel pump resistor pack/relay/ wiring system. It might be the case of a relay in the oem system not getting activated ecu wise. In other words the hi/low voltage system is the problem as it malfunctions.

Disconnect the small pump from the hi/low voltage system, and hardwire it directly to the battery, leave the big pump on the hobbs switch. See if the problem goes away.



The stock wiring can handle the amperage the 450 draws on cruising being hardwired.







Marios

 

Thanks for the response guys.

The stock low/high voltage works as it should, I have logged it. It shows 0 on boost, so it bypasses the resistor and when I lift it shows 1 and the amps go through the resistor pack. But as Marios said, it could work if I hardwire the small pump (so it sees full voltage all the time) and it flows more when the problem exists.

The lockout for the small pump is at 8 bars on 13.5V, but who knows what it is at stock low voltage mode:

https://www.fuelpumpsonline.co.uk/wa...02-44922-p.asp

 

If the low/high voltage transition worked as it should, you would not have had any issues. The logging might show that the system works and that the system switches in between the primary and secondary relay, bypassing or not accordingly the resistor pack thus both relays are activated accordingly and as they should, but that does not mean that the pump does actually get the right voltage, or that it gets the right voltage for the correct amount of time. So basically what you see on your log in regards to this, is that the ecu has triggered the bypassing/activation. Getting a log on something that appears to be ok, does not necessarily mean that it is and since you do have a problem with the small pump after a certain condition, then obviously there is a relay malfunction/drainage/shorting condition present.


You need to bypass the system and hardwire the small pump directly to battery. This should resolve the issue.





Marios