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Walbro Fp + Constant Power Pressure?

Paulusc44
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Paulusc44 Enthusiast

Paulusc44

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Hey all,

Recently went to fire up my rebuilt S1 RB25 which has had some decent upgrades carried out on it over the last 6 months..

Found the Fuel Pump wasent running (Walbro 255 L.P.H) So simply hard wired it in without using a relay and got it to work..

My Question is, under constant power can I still control fuel pressure and run it for a short time? ( I have a Japanese Adj. FPR fitted)

Is amperage flow suitable?

Cheers :)

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GTSBoy Grand Master

GTSBoy

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Of course. The whole ECU controlled 2 step voltage on the pump is only to reduce noise and fuel heating at idle. The stock FPR is easily able to control the pressure across the full range of engine demand with the stock (or larger) pump running flat out. Your aftermarket reg would be even more capable.

Paulusc44 Enthusiast

Paulusc44

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Of course. The whole ECU controlled 2 step voltage on the pump is only to reduce noise and fuel heating at idle. The stock FPR is easily able to control the pressure across the full range of engine demand with the stock (or larger) pump running flat out. Your aftermarket reg would be even more capable.

Cool, just wanted to check, I actually ended up using the pump under regular conditions (using factory relay) dont know if you remember my question I asked you about a week back about my fuel pump? Thinking the relay was dead I powered it directly with 13 v, ran it for a few seconds, and then re-connected the factory connector just to double check it wasent working and.. woolah the thing worked again without being directly powered and has been working fine ever since?

Also, am I correct in saying fuel pressure should be held in the rail at all times? (ign on and off) I can set my FPR to whatever pressure I like (45 PSI in this case) and it will stay at that pressure with the fuel pump running, but when I turn ign off, the pressure begins to drop off quite sharply? Im thinking diaphram/valve in the FPR itself? (Its new/under warranty) Obviously this doesent effect running but still..

Scott Black Rising Star

Scott Black

Posted
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Depends if your fuel pump has a check valve in it. It's not the reg letting the pressure drop yet it's dropping the other way back threw the pump. Unsure if that pump actually has a check valve or not yet that's why you loosing pressure rapidly once ign off.

Paulusc44 Enthusiast

Paulusc44

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Depends if your fuel pump has a check valve in it. It's not the reg letting the pressure drop yet it's dropping the other way back threw the pump. Unsure if that pump actually has a check valve or not yet that's why you loosing pressure rapidly once ign off.

Are there EFI fuel pumps without check-valves in them? I thought all modern fuel pumps had a check valve?

Paulusc44 Enthusiast

Paulusc44

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The check valves all leak. When you turn our Subaru off it moans like a bitch for about 5 seconds. This is why ECUs will generally run the fuel pump for a few seconds when you turn the ignition on (but not to crank)....to reprime the rail.

I can imagine over time the check valves in factory fuel pumps would leak.. It just surprises me as this is a 6 month old genuine walbro, and the check valve was working fine in it last time I checked.. (Rail held pressure etc)

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