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Fuel Pump upgrade rewiring and Dual Voltage Issue

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Hi Andre I have heard from many tuners that whenever i upgrade my fuel pump i should rewire them and give them constant volatge to ensure proper amp , however i noticed the Subaru and EVO i think uses dual voltage operation. Will I burn out the upgraded pump by running them at full voltage and will i run into rich afr spots particularly low rpm or low pulse width section with constant voltage?

Running after market pumps at constant voltage won't give you rich spots or low pulse widths as the fuel pressure regulator will ensure that the fuel rails are at a constant pressure. This means that whether your using 33% duty on a PWM control or running the pump at 14 volts the pressure in the rail itself will still be the same at low speed, its just that your returning more fuel back to the tank if your running it on 14 volts.

I can't speak on Evo's but Subaru's use a PWM to control their fuel pumps, 33, 66 and 99% duty.

This is an approach I have taken with some cars too. Often the factory wiring becomes the limiting factor when you put in s pump that draws a lot of current. The pump controllers are there to reduce noise from the fuel pump at idle and cruise, reduce fuel being unnecessarily circulated through the fuel system, and possibly lastly to extend pump life. The pump life part would be the least of my concerns if you rewrite the pump to constant voltage.

if your bigger fuel pump results in more fuel pressure then you quite likely will see the AFR move slightly rich in the areas the factory pump was at low speed.. Usually a bigger pump will however have the engine pig rich in the WOT areas of the map and that will need attention.

Actually Chris it does depend on how big you go with the fuel pump. I've seen some of the bigger drop in pumps overwhelm the factory regs ability to bypass fuel and this results in the fuel pressure jumping up a little. Of course it's dependent on how big you go on the pump front. More of an issue with some of the larger pumps designed around E85 that are common now.

Also I'll point out that on V7 onwards sti/wrx you will end up with a CEL that you need to disable if you bypass the factory speed controller. Can't fit the life of me remember the code though sorry :(

Hi guys i just recieved my pump rewire kit , however i am not sure if i should by pass the fuel pump controller because i am still on stock regulator, not sure if runn8ng 340lph pump at full power will cause my base pressure to high. I know walbro 460 will cause base pressure to rise very high but do you guys think 340lph will result same too?

I haven't run that size pump on the stock regulator and it's quite possible it will produce too much flow for the reg to control properly. Whether you need to rewire the pump directly is dependent on how hard you want to push the engine power wise though. If you are expecting to get near the pumps limit then you will be best to rewire the pump and bypass the controller.

As an example I'm still using the stock wiring in our 86 and the engine is producing more than twice stock power on E85 so in that platform I wouldn't say that bypassing the speed controller for the fuel pump is essential until you're really shooting for big power levels.

Hi Andre I kind of understand how EVO dual voltage works by using a resistor and relay on the power wire to change the voltage,

but how does Subaru uses a Ground wire from the Fuel pump controller to change its Cycle if power is constant 12 V .

Are they cycling on and off really fast to achieve this?

And even if the base pressure is high can't we just correct the issue from VE table ? Do i must buy a regulator and dial it back down to 43 psi like stock ?

Yes, thats what pulse width modulation (PWM) does. It switches the ground at variable pulsewidth which in turn controls the speed of the pump, its also used in Idle Air Control valves, Cooling Fans and in newer vehicle to control the brightness of LED lights. What you must consider is the amperage draw of what you are trying to control. ECUs internal drivers are not designed to handle lots of current so you can use solid state relays ex. Haltech p# HT030202 which in turn control whatever high amperage device you want to control.

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