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Old 01-31-2011, 11:00 AM   #1
Ryan23
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Member#: 15116
Join Date: Feb 2002
Chapter/Region: MAIC
Location: Newburg, MD
Vehicle:
2000 Ver6 STi Type-R
EJ257/GT35R

Default Fuel pressure too high

Hey Guys -
I've been experiencing some weird tuning issues with my new build. Quick synopsis:

2000 Impreza STi Version 6
Built EJ257 bottom end
P&P, chambered matched, EJ207 heads
Kelford 272 cams
EJ207 Spec-C intake manifold
Perrin V2 top feed fuel rails, stock JDM FPR
ID 1000cc injectors
ATP GT35R
Link G4 Xtreme ECU
and a bunch of other un-related stuff

We were having some tuning issues that never cropped up with the old motor (68HTA, EJ207). The old motor ran great (and still does). About a week after the new engine went in I noticed my Walbro had changed it's tone (even louder than than usual). Suspecting I may have a Walbro about to **** the bed, I swapped back to my old Group N STi pump while I awaited the forthcoming Aeromotive in-tank pump.

Got the driveability decently tuned, break in miles done and started tuning some WOT. IDC's were goofy. At 1.05 bar I ran out of injector (17.5ms IPW @ 7500 RPM). That can't be right... a couple days later my Group N fuel pump started whining too...

- Checked voltage at the pump, 12.5V at idle
- Checked FP ground, .2 ohms... good

Finally broke down and borrowed the Defi FP sensor off my GT-R. I teed it in after the fuel filter and fired it up.... woah.... 5.5 bar of fuel pressure (~80 psi). If my Group N pump is even capable of 95 psi (under boost), it probably didn't have any volume up there. That would explain some things.

FWIW, I never bothered to check the fuel pressure as I'm using a stock regulator. Lesson learned.

I know the GDB's use a FP controller that my GC doesn't have. GC's run 12.5V to the pump whenever the engine is running. I don't think that's the problem though as there are folks who bypassed the controller all together. I suppose I *could* have a faulty regulator. It came off a low mileage Spec C. I can't use my GC regulator as the bolt spacing is a little closer than the GD.

I pulled the return hose off the regulator and ran a short piece of hose into a bucket. I was thinking maybe I had a crushed return line. Primed it a few times, nope, same pressure.

Has anyone seen this before? Maybe Perrin didn't have my JDM GDB regulator in mind when they developed their top feed rails? I'm probably going to pick up an external regulator and bypass the whole Perrin regulator block. However, I wanted to run it by you guys and see what ya'll though.

Thanks,

Ryan
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Old 01-31-2011, 01:24 PM   #2
the suicidal eggroll
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2012 WRX

Default

The only thing that controls the fuel pressure is the FPR. The only time the pump will affect the fuel pressure, is if it can't keep up with the demand from the injectors, in which case the pressure will drop. If your pressure is too high, it's always going to be a problem with the FPR (or the FPR return line).

Sometimes at idle your pressure will be high simply because the FPR can't bypass enough fuel to keep the pressure low. In that case, as soon as you start driving and the injectors start pulling fuel from the system, the pressure will drop to normal. Did you watch the pressure while driving or only at idle?
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Old 01-31-2011, 05:56 PM   #3
Ryan23
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2000 Ver6 STi Type-R
EJ257/GT35R

Default

Quote:
Originally Posted by the suicidal eggroll View Post
The only thing that controls the fuel pressure is the FPR. The only time the pump will affect the fuel pressure, is if it can't keep up with the demand from the injectors, in which case the pressure will drop. If your pressure is too high, it's always going to be a problem with the FPR (or the FPR return line).

I'm sorry, perhaps I didn't articulate my post well enough. Isn't that what I just said? Reading through my post again, I'm not sure where I eluded that the pump was causing my high pressure?


Quote:

Sometimes at idle your pressure will be high simply because the FPR can't bypass enough fuel to keep the pressure low. In that case, as soon as you start driving and the injectors start pulling fuel from the system, the pressure will drop to normal. Did you watch the pressure while driving or only at idle?
I did not drive the car because, frankly, it's wrong. I've built a number of fuel systems and I've always set the base @ 40-45 psi. If my regulator isn't reducing pressure at idle than there is a good chance it's not really reducing pressure while driving. At that pressure, the fuel pump isn't flowing the correct volume. Maybe a picture will better illustrate this:



I'm not sure where the Group N pump comes in but it's probably not as good as the Walbro 255 pump. My pump is only seeing 12.5V. For reference sake, a 2.5 liter @ 7500 rpm needs roughly 150 lph of volume. There is a reason why the base fuel pressure shouldn't be set this high.

Ryan

Last edited by Ryan23; 01-31-2011 at 10:11 PM.
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Old 01-31-2011, 06:14 PM   #4
the suicidal eggroll
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Quote:
Originally Posted by Ryan23 View Post
I'm sorry, perhaps I didn't articulate my post well enough. Isn't that what I just said? Reading through my post again, I'm not sure where I eluded that the pump was causing my high pressure?
I guess I saw the thread title "fuel pressure too high", then the first half of your post was talking about the fuel pump, checking voltages, swapping pumps, etc., when none of that would have an effect if the fuel pressure was too high, since the FPR is what would be to blame.

It looks like it was more of a story though, no worries.

Yes people often have issues with their fuel pressure being too high. It either happens when they really go crazy nuts with their fuel system and exceed the bypass capacity of the FPR, or (more often) when their FPR decides to go bad and stops bypassing enough fuel to keep the pressure down. Both are pretty common.
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Old 01-31-2011, 07:58 PM   #5
Ryan23
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Join Date: Feb 2002
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Location: Newburg, MD
Vehicle:
2000 Ver6 STi Type-R
EJ257/GT35R

Default

Quote:
Originally Posted by the suicidal eggroll View Post
I guess I saw the thread title "fuel pressure too high", then the first half of your post was talking about the fuel pump, checking voltages, swapping pumps, etc., when none of that would have an effect if the fuel pressure was too high, since the FPR is what would be to blame.

It looks like it was more of a story though, no worries.

Yes people often have issues with their fuel pressure being too high. It either happens when they really go crazy nuts with their fuel system and exceed the bypass capacity of the FPR, or (more often) when their FPR decides to go bad and stops bypassing enough fuel to keep the pressure down. Both are pretty common.
I gotcha. Yeah, initially I thought I had a pump failing before I checked the fuel pressure. Out of 1000cc injectors on only a bar of boost on gas? I mean, my heads are good, but not quite that good, . So why else would I be out of fuel? I incorrectly assumed my fuel pressure would be good to go because of the stock regulator.

With that said, I guess I was looking to see if anyone else had seen a problem with Perrin rails, stock regulator and high fuel pressure? Using a single Group N pump, it just seems unlikely that my FPR can't bypass enough. A stuck regulator is plausible but just seems unusual.

I suppose the next step would be to get past that tough crimp clamp, pull the reg out of the loop, and see if my fuel pressure falls off.

Ryan
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Old 02-01-2011, 05:13 AM   #6
Ryan23
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Member#: 15116
Join Date: Feb 2002
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Vehicle:
2000 Ver6 STi Type-R
EJ257/GT35R

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Just as a followup:

I pulled the regulator feed off and ran it into a bucket. Zero psi when the pump primes (good!). I then bypassed the Perrin junction block and installed a Nismo adjustable regulator I had laying around. Without even adjusting the regulator, spot on 3 bar off fuel pressure with the vacuum hose pulled. Bingo!

How will ever explain to my friends that I'm now running a Nismo part on my STi Time to get back to tuning...

Ryan
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Old 02-04-2011, 11:55 PM   #7
Ryan23
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Member#: 15116
Join Date: Feb 2002
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Location: Newburg, MD
Vehicle:
2000 Ver6 STi Type-R
EJ257/GT35R

Default

Map required a re-tune. IPW came down quite a bit up top (duh!). I'm now sitting at 65% IDC @ 205 kpa of boost @ 7000 RPM. AFR's hovering mid 11's.

Does anyone have a log of their IDC's from a similar setup at that RPM/AFR on a 2.5? Just curious how close my fueling requirements are to others. Using the universal calc @ Stealth 316, It's figuring I should be ~58% IDC on 1000cc injectors.

Thanks,

Ryan
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