Replace Fuel Pressure Regulator on 1999 Legacy B4 RSK

[Bulldog37]

Hello from America.  I have a 1999 Legacy B4 RSK (EJ208 Dual Turbo) that I need to do a Fuel Pressure Regulator change on.  Should be an easy job, right.....Not really.  On my model, the FPR looks like it lives on the very end of the fuel rail back towrds the drivers side turbo.  Not real easy way to get to it that I can see without removing the intake.  Is this a true statement?  Has anyone done this on theirs?  Any tips, tricks or cheat codes are gretaly appreciated.  

Edited January 28 by Bulldog37
Spelling.

[richie2990]

Hi no not easy to remove without taking intake off and , I'm sure the regulator is a part of the fuel rail if I remember correctly , pink injectors are easier to remove than the side feed yellow ones to get fuel rail off too

 

Don't tear primary turbo intake hose when taking intake off ,they are brittle after a few heat cycles , I replaced mine with a silicone replica type 

[Bulldog37]

Richie2990.   Thanks for info and confirmation.   I will start to wrestle with this soon.  I will update of my woe 😱. 
 

John 

[richie2990]

No problem and if you need to know anything else just message me , been working on these cars for well ove 15 years haha 

[Bulldog37]

Hi Richie,   
          Thanks for the info and the offer.  So I will ask for a bit of advice.  My 1999 B4 has, what we call here in America, the Subie Stumble.  It hesitates just a bit between 2,500 and 3,500 rpm.  For about half a second.   Once the stumble is done, it accelerates like normal.   Things I have done so far:

1.  New plugs and coil packs. 
2.  New fuel filter. 
3.  New knock sensor. 
4.  New fuel line dampers.  Both of them.  
5.  Cleaned idle sensor.  
6.  Cleaned MAF.  
 

Next thing is fuel pressure regulator, but that was the original question.  Any other things to check before the pressure regulator?   Thanks. 
 

John

[richie2990]

It's always to get to a good baseline with service parts , I have had this issue before and the boost / map sensor switch solenoid wasn't switching in the black box I would check that for a start 

[richie2990]

6 hours ago, richie2990 said:

It's always to get to a good baseline with service parts , I have had this issue before and the boost / map sensor switch solenoid wasn't switching in the black box I would check that for a start and also slow response 02 sensor can cause similar issues too , if you are able to see live data you should be able to view the sensor outputs , also when they go from closed loop to open loop they can also do this haha so you have done the service items,I would be looking at data to pin point what the ECU is seeing, have you measured fuel pressure? I have never had issues with that before, but some models pulse width modulate fuel pump which can be see on data pids which goes from 33% duty to 100 but just another thing to look at 

 

[Joker]

 

On 2/03/2025 at 1:19 AM, Bulldog37 said:

 It hesitates just a bit between 2,500 and 3,500 rpm.  For about half a second.   Once the stumble is done, it accelerates like normal.  

 

that's a little low in the rev range but "could" be what we call the Valley of Death

 

is the changeover point between Single small Primary and Parallel Twin turbo mode (both)

 

I'll see if I can find a Dyno graph of my BG5c in the garage thread or archives

 

photo bucket has eaten the images (but I know I have them @ work so please wait 10-12 hours hah

 

[Joker]

This is one of the earliest Dyno Sheets of my TT (the 1998 BG5c) = 160kw

 

 

bonus actual video of the Rolling Road setup & run on a Digital Camera with no Mic

 

 

October 2004 not long after I traded in the 1990 BC GT for it

 

Sorry no RPM's but a notable dip in power / torque : No-ones been able to explain the funky backwards lines but I think you can see the VOD there on the PSI chart

 

2007 Hub-dyno Petone

 

 

 

 

I call it 180 kw WITH Boost Spike : split 4mm or 6mm hoses on the top of the intake

[Joker]

so yeah between 4 & 5k rev range

[richie2990]

i had a brainwave about this issue and you could be on the right path , i was looking at data on my car and noticed the fuel compensation pids and forgot about them and  i remember subaru added software instead of fixing the issue,  The fuel compensation values can be adjusted but the root cause is the pulsing in the fuel system causing surging/ stumble at around the rpm you are describing , adding bigger injectors makes it worse so i was unsure if the fuel line mod fixed this issue, i have not had it with any of my cars but have heard of this issue years ago 

[Gripless]

@Joker No-ones been able to explain the funky backwards lines but I think you can see the VOD there on the PSI chart.
 

The plot X axis is road speed and the line from data logged over time plotted in time order, so the run started at 90kph then dipped back to 85kph 

 

likely caused by operator error, you can rule out car if you have other good plots.

-Wheelspin from not being strapped down well. 1 strap and not at steep angle rushed at dyno day. Or too much power applied too quickly.

-starting run and not giving it more gas so dyno load drags speed down.  

 

[boon]

Was it a slushbox? Old autos sometimes do that on the dyno.

[Joker]

5 hours ago, boon said:

Was it a slushbox? Old autos sometimes do that on the dyno.

 

nope if you're asking me Manuel