AFPR options and stock fuel pressure #'s?

[my3awds]

I was wondering if there any bolt-on type adjustable fuel pressure regulators for our engines. I tried to search on egay but all they had was a bunch of cheap looking universal kits. Also, what is the stock psi through the rail with and without a vacuum source on the fpr? 45psi?

Manny~

[vrg3]

Standard pressure is 2.5 bar over manifold pressure. So roughly 36 psi with the hose disconnected, and roughly 26 psi with it connected at idle.

Any FPR that uses 5/16" hose barb fittings for its inlet and outlet can be easily plumbed into our stock return line. As long as you're not looking to reduce pressure below stock (which is usually a bad idea anyway because it hurts fuel atomization), you can leave the stock FPR in place.

[my3awds]

Awsome, thanks.

[pisces_0]

Standard pressure is 2.5 bar over manifold pressure. So roughly 36 psi with the hose disconnected, and roughly 26 psi with it connected at idle.

In doing some searching for the stock fuel pressure I've come across a few dissenting opinions on the stock pressure numbers. Some say 36.5 psi while others say 43.5 psi. For a turbo engine, which is correct?

The FSM shows a flow rate for the fuel pump in non-turbo cars at 36.3 psi and turbo cars at 43.4 psi. I'm assuming these would be the numbers I'm after, I just want to get some confirmation on this one.

[Legacy777]

Myself & Ryan have measured the fuel pressure at idle. None of the numbers here are really actual numbers.

http://bbs.legacycentral.org/viewtopic. ... l+pressure
http://bbs.legacycentral.org/viewtopic. ... 538#183538

[pisces_0]

http://bbs.legacycentral.org/viewtopic. ... l+pressure
http://bbs.legacycentral.org/viewtopic. ... 538#183538

Thanks! From the pressure numbers in those threads it looks like the turbo engine/ECU expects to see ~43.5 psi.

Also, straight out of the FSM:

MPFI Turbo
Fuel Pump
Type: Impeller
Discharge Pressure: 299.1 kPa (3.05 kg/cm2, 43.4 psi)
Discharge Flow: More than 150l (39.6 US gal, 33.0 Imp gal)/h
[12V at 299.1 kPa (3.05 kg/cm2, 43.4 psi)]

[Legacy777]

No....that's not really what's being said.

The threads indicate what the fuel pressure is at idle with and without the fuel pressure regulator vacuum line hooked up.

The fuel pump data is just that, what the pump is capable of flowing at a certain pressure. As the fuel pressure regulator pinches down the return line, pressure will increase and flow will decrease.

So as boost builds fuel pressure will increase. I don't believe anyone has logged fuel pressure for different boost levels. Plus, the fuel pressure is likely to be different at higher boost levels when a high flow fuel pump is used compared to the stock pump.

[pisces_0]

The threads indicate what the fuel pressure is at idle with and without the fuel pressure regulator vacuum line hooked up.

I understand what the two threads are covering. My concern is what the fuel pressure should be for a turbo car/ECU with the vacuum line disconnected. Per the factory manual, it looks like an non-turbo car should see ~36.5 psi and a turbo car should see ~43.5 psi with the vacuum line disconnected.

I'm asking because I'll be installing a Walbro 255 and AFPR to dial the fuel pressure back down to where it should be. The higher flow and pressure will quickly overrun the stock fuel pressure regulator.

So as boost builds fuel pressure will increase. I don't believe anyone has logged fuel pressure for different boost levels. Plus, the fuel pressure is likely to be different at higher boost levels when a high flow fuel pump is used compared to the stock pump.

As boost builds, fuel pressure should increase with it linearly on a 1:1 basis. The fuel maps in the ECU, and thus the pulsewidth that's sent to the injectors, are based off of a certain fuel pressure over manifold pressure which should always stay constant. If you install a higher flow fuel pump (Walbro 255, for instance) fuel pressure rises exponentially with manifold pressure because the stock fuel pressure regulator can't bypass enough fuel to keep up the 1:1 ratio. Fuel pressure starts to rise above the 1:1 ratio, but the ECU doesn't know this and goes to its fuel look-up table as it always has and delivers the programmed amount of fuel based off of airflow, manifold pressure, TPS, coolant temp sensor, etc. and you end up with a rich condition. With a base fuel pressure (no vacuum line connected to the FPR) of 43.5 psi you should see 48.5 psi of of fuel pressure at 5 psi of boost, 53.5 psi of fuel pressure at 10 psi of boost, 58.5 psi of fuel pressure at 15 psi of boost, and so on and so forth.

Does everyone here who installs a higher flow fuel pump just keep the stock fuel pressure regulator?!

I've been a long time DSM'er and fuel pressure regulator overrun with a higher flow fuel pump is a well known and documented problem with those cars. When installing a Walbro 255, or anything larger, an adjustable fuel pressure regulator is a must to bring fuel pressure back to where the ECU needs it to be for proper fueling.

[Legacy777]

A lot of subaru guys install the walbro 255 pumps without any problems.

I believe our stock fpr can handle/bypass the additional flow from the walbro pump. So the issues you mentioned aren't really an issue.

If you have a stock pump in your car, hook a gauge up and see what sort of pressures you're seeing. If someone does this for a stock turbo legacy pump and monitors fuel pressure as they build boost, I should be able to do the same with my car with walbro.

The numbers you're finding in the factory manuals for the pumps are NOT what the fuel pressure should be at idle. What they give is a specific operating point on a pump curve.

If you knew the exact pump head in the system and had a pump curve you could look on it for a given pressure or flow rate and find the corresponding information.

Like I mentioned, a lot of guys have installed these pumps and don't have any problems. I do feel your concerns about fueling & pressure are well merited, but I don't believe anyone has done the specific tests needed to determine whether the stock fpr can bypass the added flow.

[pisces_0]

A lot of subaru guys install the walbro 255 pumps without any problems.

Wow, quite different than in the DSM world then! Anything more than ~200 lph and the stock 4G63T FPR is overrun. Base pressure goes through the roof and as boost rises fuel pressure is far from linear. Throws the closed-loop fuel trims all out of whack and the car will run quite rich at WOT. Mileage and smooth power delivery go out the window.

I believe our stock fpr can handle/bypass the additional flow from the walbro pump. So the issues you mentioned aren't really an issue.

*wipes brow*
WHEW! Another part I won't really have to worry about in my Frankenstein-esque swap. See below...

If you have a stock pump in your car, hook a gauge up and see what sort of pressures you're seeing. If someone does this for a stock turbo legacy pump and monitors fuel pressure as they build boost, I should be able to do the same with my car with walbro.

Sorry, no stock turbo Legacy pump to compare to. I'm hip deep in swapping an EJ22T and dual-range trans into a '94 Loyale 4WD. My Talon is fun in the summer, but just doesn't have the ground clearance for the deep snow here in northern MN. This Loyale has been my daily for 4+ years and while the EA82 and push-button 4WD have dutifully served me in all conditions I've thrown them into, my constant need for tinkering and upgrading has surfaced again. Also, I'm VERY impressed with the numbers and durability I've seen from some of your EJ22Ts. I always thought the 4G63T was uncontested as one of the most stout turbo 4s, but it looks like a well-prepped EJ22T can definitely hold its own too!

The numbers you're finding in the factory manuals for the pumps are NOT what the fuel pressure should be at idle. What they give is a specific operating point on a pump curve.

My misinterpretation then. Again going back to my DSM roots, all the stock fuel pressure numbers are listed in the FSM as base fuel pump pressure output and flow numbers (as I cited above from the Subie FSM). I was assuming it may be similar in the Subie world, but I guess not.

Like I mentioned, a lot of guys have installed these pumps and don't have any problems. I do feel your concerns about fueling & pressure are well merited, but I don't believe anyone has done the specific tests needed to determine whether the stock fpr can bypass the added flow.

I may have to do a little investigating on this then to see what the stock turbo Legacy FPR is set to. I may start by installing a lower flowing pump, one sure not to overrun the FPR, like the stock SPFI EA82 pump, measure fuel pressure and watch the fuel trims. From everything I've seen and read it looks to be in the neighborhood of low-40's, but experimentation and data collection will soon shed some light on this.

Thanks again for all the help and patience guys. Info somewhat crosses over from DSMs, but I've been reading and researching Subie info like mad for the past few months.

[Binford]

How far north is northern Mn?

[pisces_0]

How far north is northern MN?

Proctor, just outside of Duluth, with regular runs up the North Shore and visits to Ely on occasion. Far enough north for ya?

[Legacy777]

Thanks again for all the help and patience guys. Info somewhat crosses over from DSMs, but I've been reading and researching Subie info like mad for the past few months.

No problem. Do let us know what you come up with on your tests.