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Old 04-09-2021, 11:27 PM   #1
Subi3b00bi3
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2003 Matte White Wrx
2006 WRB STi 2007 SWP STi

Default Fuel Pressure Loss Help!

Hey guys been tackling this for a few months now and can't figure this out for the life of me. Basically when I get into boost my fuel pressure drops instead of rises. Base pressure is set at 45psi and I'm only on my 2nd or 3rd revision at 20psi and fuel pressure drops to 25psi only towards red line. Daily driving everything is fine and fp lingers in the 45ish range. My injectors shouldn't be hitting over 100%idc but are compensating for the lack of fuel pressure. If I'm not mistaken they should be around 60%idc if I'm not mistaken.



mods:
walbro 450 pump (274) new less than 800 miles

id1300 recently sent to ID to be cleaned and flow tested
Fuel Labs 6 micron inline filter with new filter
iag rails and fuel lines
fore innovations t2i fpr installed just a few days ago (fuel labs Fpr for sale with gauge btw lol)
cobb flex fuel kit
cobb fuel pressure sensor
omni 3 bar map sensor
johnson tuning iat sensor


bcp x500+ turbo
el header up pipe full catless exhaust
manley htuff rods wisco pistons
stage 1 bc racing cams and valves


i know there are a few other threads like this but no one ever posted if they solved it or not.
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Old 04-10-2021, 11:28 AM   #2
JSR84
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How is that pump wired?
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Old 04-10-2021, 11:51 PM   #3
Subi3b00bi3
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2006 WRB STi 2007 SWP STi

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hard wired...it happens when wiring is oem wired or hard wired pump
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Old 04-12-2021, 12:45 PM   #4
JSR84
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You'll need to go through the fuel system front the back. There can be several possibilities.
1) The pump is NFG. I know it's new, but stranger things have happened.

2) There is a restriction somewhere between the pump outlet and the FPR. At low demands the restriction has a negligible effect, but once demand increases the restriction becomes more apparent. A common restriction would be a clogged fuel filter.

3) The pump inlet is restricted. I had the exact issue on a 2005 Ford Focus. The car would run fine under low loads light to light, but the second you put any demand on it, the engine would feel like it hit a soft rev limiter. Eventually it got bad enough that even low load started showing issues. When scanning fuel pressure you could see it fall off as the demand for fuel flow increased. First thing I did was change the fuel filter, which helped, but didn't completely solve the issue. I then went to replace the pump, but when I got it out of the tank I found the suction sock was clogged with sludge from the bottom of the fuel tank. I ended up cleaning the tank and replacing the pump and sock which solved the issue.

4) The FPR may be bad. Does you fuel pressure track vacuum like it should? What I mean by that is, if vacuum is reading -10PSI does the fuel pressure = Base - 10PSI? Even if it does, there could be an issue in the regulator that only manifests on the boost side of things.

5) Fuel vaporization, but this generally only happens with higher fuel temperatures and with pumps that are running in the upper end of their rated flow capacity. The hot fuel combined with high suction levels at the pump inlet cause the fuel to vaporize inside the pump housing.

You're going to have to systematically eliminate components and scenarios. Start with the free things like ensuring there aren't any restrictions in the system on both the pressure and suction side, even if it means pulling the system apart. Then move to looking at individual components.
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Old 04-13-2021, 12:00 AM   #5
Subi3b00bi3
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That makes sense. I just order a new fuel sock. This is my 4th, maybe 5th, fuel pump testing the issue due to the possibility that it was a "bad" pump out the box. Also this is my 3rd fuel pressure regulator and 3rd brand of regulator. After changing the regulator my IDC has gone down but FP still drops just as bad. My bet after reading what you said it could be a possibility my sock is clogged. Other than the hard lines from the firewall to the tank that's the only other oem part of the fuel system left I haven't replaced.
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Old 04-14-2021, 11:55 AM   #6
JSR84
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Please report back when you figure it out. I would like to know.

Also check that you're getting a good vac/boost reference to you FPR.

Good luck.
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Old 04-14-2021, 10:09 PM   #7
Subi3b00bi3
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I for sure will. I hate it when people don't update their problem threads.
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Old 04-23-2021, 01:23 AM   #8
Subi3b00bi3
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Fuel sock did nothing. Going to get vac leak test
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Old 05-05-2021, 09:13 AM   #9
MiikaS
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What kind of wire used to wire the pump? That pump needs a lot of power when running full and stock wiring is really bad for it. We had one Forester on a dyno that had same pump and stock controller and it acts quite same when it gets to boost.
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Old 05-05-2021, 06:44 PM   #10
Subi3b00bi3
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Quote:
Originally Posted by MiikaS View Post
What kind of wire used to wire the pump? That pump needs a lot of power when running full and stock wiring is really bad for it. We had one Forester on a dyno that had same pump and stock controller and it acts quite same when it gets to boost.
Hmm good question. It's a fairly old kit I've been running for years. Maybe it's finally showing its age? I'm out of town for a bit but when I get back I'll check on that and a vac leak test
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Old 05-14-2021, 12:43 PM   #11
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As others have stated this sounds like a wiring issue or possible dying pump, even if it's new. That pump draws a lot of amperage and needs a decent gauge wire if you are hard-wiring all the way from the engine bay to the tank. Even with good wiring there will be voltage drop due to the distance. If the pump is not seeing enough amperage it will cause it to prematurely die, ask me how I know. A well placed and designed surge tank is the best way to go in the long run.
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Old 05-20-2021, 07:37 PM   #12
Subi3b00bi3
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Quote:
Originally Posted by umscooby View Post
As others have stated this sounds like a wiring issue or possible dying pump, even if it's new. That pump draws a lot of amperage and needs a decent gauge wire if you are hard-wiring all the way from the engine bay to the tank. Even with good wiring there will be voltage drop due to the distance. If the pump is not seeing enough amperage it will cause it to prematurely die, ask me how I know. A well placed and designed surge tank is the best way to go in the long run.
I'm going to purchase the iwire kit next and see if that fixes my issue.
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Old 05-20-2021, 08:40 PM   #13
Marvick08GT
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Replace the fuel filter.. The sock that is on the pump is NOT the filter. The filter is built into the fuel pump assembly, but can be replaced ( the lower bucket )
Good luck!
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Old 05-26-2021, 10:26 PM   #14
Subi3b00bi3
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Quote:
Originally Posted by Marvick08GT View Post
Replace the fuel filter.. The sock that is on the pump is NOT the filter. The filter is built into the fuel pump assembly, but can be replaced ( the lower bucket )
Good luck!
Thank you but I've already done that recently. I do not have the in tank filter. I have a inline race filter .
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Old 06-23-2021, 04:43 PM   #15
e_navarre
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I’m having the same issue and running the same parts. I replaced my pump and it didn’t do anything. FPR is my guess. Since you’re dropping fuel pressure at WOT it seems that there’s something wrong with the regulator since it should be a raising fuel pressure 1:1 with boost.
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Old 07-17-2021, 03:31 PM   #16
Subi3b00bi3
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2006 WRB STi 2007 SWP STi

Default

Quote:
Originally Posted by e_navarre View Post
I’m having the same issue and running the same parts. I replaced my pump and it didn’t do anything. FPR is my guess. Since you’re dropping fuel pressure at WOT it seems that there’s something wrong with the regulator since it should be a raising fuel pressure 1:1 with boost.
I replaced the regulator 3 times with same results. Im pulling out the hardwire kit and installing an iwire fuel pump control kit instead and see if that fixes it. I'm wondering if it's dropping voltage too end and the pump isn't getting enough voltage to keep up.
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Old 07-17-2021, 05:45 PM   #17
e_navarre
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Quote:
Originally Posted by Subi3b00bi3 View Post
I replaced the regulator 3 times with same results. Im pulling out the hardwire kit and installing an iwire fuel pump control kit instead and see if that fixes it. I'm wondering if it's dropping voltage too end and the pump isn't getting enough voltage to keep up.
Let me know if that fixes it, I’ve replaced everything in my fueling system and I’m ripping my hair out trying to figure it out
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Old 08-10-2021, 08:16 PM   #18
Thorium06
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Assuming you are speed density. Did this issue start as a new build or did it develop?

If its a new build and SD on a AP3, it could be hitting the max allowed VE on the MAF table. COBB SD for whatever reason still references the MAF table which oddly has a very low VE limit. Bumping that up might solve your issue.
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Old 09-23-2021, 12:25 PM   #19
Brandon Wedderburn
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Default Similar issue

Quote:
Originally Posted by Subi3b00bi3 View Post
Hey guys been tackling this for a few months now and can't figure this out for the life of me. Basically when I get into boost my fuel pressure drops instead of rises. Base pressure is set at 45psi and I'm only on my 2nd or 3rd revision at 20psi and fuel pressure drops to 25psi only towards red line. Daily driving everything is fine and fp lingers in the 45ish range. My injectors shouldn't be hitting over 100%idc but are compensating for the lack of fuel pressure. If I'm not mistaken they should be around 60%idc if I'm not mistaken.



mods:
walbro 450 pump (274) new less than 800 miles

id1300 recently sent to ID to be cleaned and flow tested
Fuel Labs 6 micron inline filter with new filter
iag rails and fuel lines
fore innovations t2i fpr installed just a few days ago (fuel labs Fpr for sale with gauge btw lol)
cobb flex fuel kit
cobb fuel pressure sensor
omni 3 bar map sensor
johnson tuning iat sensor


bcp x500+ turbo
el header up pipe full catless exhaust
manley htuff rods wisco pistons
stage 1 bc racing cams and valves


i know there are a few other threads like this but no one ever posted if they solved it or not.
Did you ever solve this issue?
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