So lets say that i have a radium double pump hanger with a single walbro 450lph fuel pump in it which also includes the radium upgraded siphon. And lets say i have the full radium fuel rail with rail mounted fuel pressure regulator and fuel pulsation damper, filter, and larger supply line. The factroy evo 8 fuel pump wiring uses a double relay system that either provides high or low voltage to the pump if i'm not mistaken. Is this wiring/relay configuration safe for the 450lph walbro? If not should i bother trying to run the factory 2 relay system? Can the factory ecu be configured to run a single relay? What do i need to make sure i tell a tuner about my configuration to make sure he modifies tables correctly? I have read a lot of weird stories about fuel pump or wiring/relawy upgrades that caused a bunch of tuning issues. I'm just trying to make sure that i do this correctly. Would i be better off rewiring the factory relays with larger wiring? Has this been covered by a good write up?

 

You could get many different answers to this question. One thing I can tell you pretty much for sure is that the peak current draw on a Walbro 450 will be around 22 amps. From what I have read, the peak current draw for the stock pump is meant to be about 12-15 amps. I don't know if there's anyone out there who's done testing or exact calculations, but from what I know running a pump that draws that much additional current on stock wiring is asking for trouble. I won't say it's not possible, there's probably people out there doing it, but I wouldn't recommend it.

Most people hardwire their aftermarket fuel pump direct from the battery with a relay. This provides more consistent voltage and allows for lower gauge wiring direct to the pump which is safer for high current draw fuel pumps. However, a lot of these folks also report running rich at idle because the ECU and stock wiring deliberately undervolts the fuel pump at low RPMs to avoid overrunning the stock FPR and fuel return system.

With a Radium FPR and the hanger with the larger siphon, based on what I have read you SHOULD be okay, but I don't think anyone has done testing of that particular item, because I was asking around about it a few months ago. I am curious if a larger fuel return line is required to truly alleviate this problem or if a lot of people just live with a slightly rich idle and tune it out as best they can. I unfortunately don't know the answer to that as it doesn't seem to be something that a lot of people focus on.

There used to be people on this forum trying to figure out how to preserve the factory undervolting system, and they came up with methods that don't seem to have really caught on. I am also looking at a larger fuel pump and I have been wondering about using a brushless motor as the controller might allow you to adjust voltage to the pump in a manner similar to the factory ECU.

 

this is awesome. I really appreciate this reply. So basically it seems like the factory wiring idea is pretty neat. The issue I’m wondering about is, can the factory ecu be programmed for a single relay and function properly as far as idle afr? I would hate to only focus on the full throttle fuel delivery. I really want to do the best job possible. I looked into the current draw for this pump and it seems like you’re right. It can hit over 20 amps given certain circumstances. What I was reading was you should go with a 30amp rated relay to trigger this pump. I’m wondering if I should just redo the factory relay/ low voltage design just with more robust relays and larger wiring that is rated for the max draw from this pump. That seems like that might be the coolest option.

 

Typically, hardwiring the fuel pump involves running wiring direct from the battery with a relay that sends current to the pump only when the ignition is on. This gives you constant/max voltage and current to the pump at all times. With a large fuel pump like the 450, this results in most people running rich at idle due to high pressure in the fuel rail with the stock fuel system. I have read that people alleviate this by getting aftermarket FPRs and drilling out the venturi pump in the fuel pump hanger but I have never seen any data, just people claiming that it solved the issue. The issue nobody talks about is that increasing throughput of fuel to the engine is also going to raise the temperature of the fuel in the fuel tank. If fuel passes through your hot fuel rail and the return system and gets dumped back into the tank, over time that heat builds up which causes problems on its own.

As I said there are forum users here who have come up with a way of using boost pressure to simulate the undervolting of the fuel pump at idle via a hobbs switch (search for posts on this topic by Mrfred). I can't really comment on this as this is something I have zero experience with, but it makes sense on a surface level. As I said in my first post it is not something that seems to have caught on widely, but a lot of people just go with whatever's easy when it comes to modding.

I can't comment on rewiring the stock fuel system. Not sure how feasible it is. You would have to know where the stock wiring's failure points are. The folks who came up with the hobbs switch solution are pretty smart though, and there's probably a reason why nobody's tried that before.

As I said in the beginning I think the best solution nowadays might be to hardwire a brushless fuel pump with a digital controller which would allow you to program it for low/high fuel pressure in the same way as the stock system, just without the stock system's limitations.