Welcome to the North American Subaru Impreza Owners Club Wednesday August 27, 2014
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC Technical > Normally Aspirated Powertrain

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 03-24-2003, 11:19 AM   #1
jeffg
Scooby Guru
 
Member#: 2958
Join Date: Nov 2000
Chapter/Region: NWIC
Vehicle:
2001 WRX (GC8)

Default Fuel Pressure and running rich

I was wondering if lowering the fuel pressure would help our cars from running to rich. Is there a minimum fuel pressure we should not go under?

I assume that you would need an adjustable fuel pressure regulator, but would a restrictor in the vacumn line that goes to the FPR work? Kind of like the used on WRXs to control boost?

I imagine if you lowered the vacumn the FPR sees there is a possibility that you could end up lean at high throttle precentage, but it seems like we have a lot of room to work with.

J
* Registered users of the site do not see these ads.
jeffg is offline   Reply With Quote
Old 03-24-2003, 12:37 PM   #2
nySulli
Scooby Specialist
 
Member#: 32617
Join Date: Feb 2003
Chapter/Region: Tri-State
Location: NY
Vehicle:
2008 STi
DGM

Default

i wouldn't screw around with the fuel pressure, if you want to run leaner then i'd just go with some engine managment and adjust the fuel map
nySulli is offline   Reply With Quote
Old 03-24-2003, 01:31 PM   #3
jeffg
Scooby Guru
 
Member#: 2958
Join Date: Nov 2000
Chapter/Region: NWIC
Vehicle:
2001 WRX (GC8)

Default

While I value you comments, the possibility of a near free way to slightly lean the air/fuel ratio is worth investigating.

To play around, I moved the vacumn source for my stock FPR to the vacumn port on the top of the intake manifold, rather than the one on the #3 runner. The fuel pressure dropped about 2 psi under cruising (low throttle precentage), but jumped right back to normal at idle (closed throttle) and heavy acceleration (high throttle precentage).

My EGTS went up ~75-100 depending on throttle application. Right now I am running at ~1400 @75 on the freeway with the cruise set, and about 1300 running around town. My EGT is in the #3 header primary.

J
jeffg is offline   Reply With Quote
Old 03-24-2003, 01:50 PM   #4
Legacy777
Scooby Guru
 
Member#: 4800
Join Date: Mar 2001
Chapter/Region: TXIC
Location: Houston, Tx
Vehicle:
1990 Legacy & 97 OBS
AWD 6MT EJ22T AWIC Swap

Default

Which line did you tap into on top of the manifold? Was there some other line attached at that point?

Your findings do make sense.....there's going to be more vacuum in the center of the manifold then in one particular intake runner.

But I would keep an eye on things.....
Legacy777 is offline   Reply With Quote
Old 03-24-2003, 03:27 PM   #5
jeffg
Scooby Guru
 
Member#: 2958
Join Date: Nov 2000
Chapter/Region: NWIC
Vehicle:
2001 WRX (GC8)

Default

The line I tapped into origionally went to the evap emissions valve. My valve is broken so there was no line on this port. I had it blocked with a plug.

I will keep an eye on the car and see how it turns out.

J
jeffg is offline   Reply With Quote
Old 03-24-2003, 08:51 PM   #6
Legacy777
Scooby Guru
 
Member#: 4800
Join Date: Mar 2001
Chapter/Region: TXIC
Location: Houston, Tx
Vehicle:
1990 Legacy & 97 OBS
AWD 6MT EJ22T AWIC Swap

Default

Quote:
Originally posted by jeffg
The line I tapped into origionally went to the evap emissions valve. My valve is broken so there was no line on this port. I had it blocked with a plug.

I will keep an eye on the car and see how it turns out.

J
There is a problem with doing this.......the canister purge valve tube only sees vacuum when the throttle is open.

So at idle the fpr isn't seeing any vacuum.

Unless of course you've modified things a little, or they have changed where the canister purge valve hooks up.
Legacy777 is offline   Reply With Quote
Old 03-25-2003, 08:51 AM   #7
Hawk296
Scooby Specialist
 
Member#: 14555
Join Date: Jan 2002
Chapter/Region: MWSOC
Location: Troy, MI
Vehicle:
1995 Impreza L
Baja

Default

I was considering tweaking the Fuel pressure regulator myself after my 2.5l swap cause with the 1.8l ECU it runs really rich. Im looking for a totally cheap way to fix that problem. ide like to learn more of this.
Hawk296 is offline   Reply With Quote
Old 03-25-2003, 01:20 PM   #8
jeffg
Scooby Guru
 
Member#: 2958
Join Date: Nov 2000
Chapter/Region: NWIC
Vehicle:
2001 WRX (GC8)

Default

Quote:
Originally posted by legacy777


There is a problem with doing this.......the canister purge valve tube only sees vacuum when the throttle is open.

So at idle the fpr isn't seeing any vacuum.

Unless of course you've modified things a little, or they have changed where the canister purge valve hooks up.
Can you explain to me how this is different from where the vacumn line was origionally connected?

I can imagine that there is some vacumn in the runner going to the cylinder because of the smaller immediate volumn, but really the intake runner and the intake phenum (spelling?) are the same air space, so vacumn should be the same at both parts. Obviously this is incorrect because I see a difference in fuel pressure.
Further problems could exist if you left the purge vavle connected to this same vacumn line. Since my purge valve is broken I had no vacumn hose on this port, just a cap.

anyway, I am going to keep it this way and watch for problems. So far it seems to be working just fine. I have an autocross this Sunday and I will keep an eye on things to see how it handles aggressive driving.

J
jeffg is offline   Reply With Quote
Old 03-25-2003, 01:45 PM   #9
Legacy777
Scooby Guru
 
Member#: 4800
Join Date: Mar 2001
Chapter/Region: TXIC
Location: Houston, Tx
Vehicle:
1990 Legacy & 97 OBS
AWD 6MT EJ22T AWIC Swap

Default

Quote:
Originally posted by jeffg


Can you explain to me how this is different from where the vacumn line was origionally connected?

I can imagine that there is some vacumn in the runner going to the cylinder because of the smaller immediate volumn, but really the intake runner and the intake phenum (spelling?) are the same air space, so vacumn should be the same at both parts. Obviously this is incorrect because I see a difference in fuel pressure.
Further problems could exist if you left the purge vavle connected to this same vacumn line. Since my purge valve is broken I had no vacumn hose on this port, just a cap.

anyway, I am going to keep it this way and watch for problems. So far it seems to be working just fine. I have an autocross this Sunday and I will keep an eye on things to see how it handles aggressive driving.

J
Well.....not knowing 100% thatyour TB/intake is setup the same way as mine.....I'm going to explain why it wouldn't be good to do what you did on my car.

If you can get a hold of some pictures of your engine and exactly where the vacuum tube is located, I should be able to tell you whether it's the same setup or different as mine.

On my car the vacuum line on the TB that the CPV hooks into is right on the edge of where the throttle plate sits.

When the throttle is closed the vacuum hole/source is behind the throttle plate and there is no vacuum. When you open the throttle vacuum is created at that source.

The way the CPV works is that the charcoal canister absorbs excess fuel vapors. When engine rpm is above a certain point for more then a specified time....the ECU sends a signal to the CPV which opens up, and allows the vacuum from the intake manifold to suck up those fuel vapors in the charcoal canister to be burned in the engine.

That is how things work on my car. There is a chance they have changed how/when this operation occurs and they may just give it a constant vacuum.

Have you hooked a vacuum gauge up to both locations and read vacuum and see how it changes with a change in throttle?

I would suggest doing this, that way you have an actual number/gauge needle and you can compare the two vacuum sources. Do this, see what you get, and if they are different, post what the differences are, and we can try and discuss the reasons why.

Josh
Legacy777 is offline   Reply With Quote
Old 03-25-2003, 01:55 PM   #10
jeffg
Scooby Guru
 
Member#: 2958
Join Date: Nov 2000
Chapter/Region: NWIC
Vehicle:
2001 WRX (GC8)

Default

Josh,

I have found the problem. the purge valve vacumn port on the EJ25 is well behind the TB. It is tapped into the actual intake manifold, rather than the TB housing. I can see on your car where the vacumn port is on the wrong side of the TB, where you would be in trouble.

I guess what it comes down to is that fact that all I did is move the vacumn hose from a single runner of the intake manifold to a port on the phelum.

My idle fuel pressure is exactly the same. The only thing that is really changed is the low throttle precentage fuel pressure, which dropped by about 2 psi.

J
jeffg is offline   Reply With Quote
Old 03-25-2003, 06:30 PM   #11
Legacy777
Scooby Guru
 
Member#: 4800
Join Date: Mar 2001
Chapter/Region: TXIC
Location: Houston, Tx
Vehicle:
1990 Legacy & 97 OBS
AWD 6MT EJ22T AWIC Swap

Default

hmmmm......anyway you could get some vacuum readings off the two ports?

What sort of mods do you have on the car? Do you have an intake of some sorts?
Legacy777 is offline   Reply With Quote
Old 03-26-2003, 11:37 AM   #12
jeffg
Scooby Guru
 
Member#: 2958
Join Date: Nov 2000
Chapter/Region: NWIC
Vehicle:
2001 WRX (GC8)

Default

I do not have an actually vacumn guage but I can try and borrow one.

I do have a cobb CAI, but I dont think that would really effect this. I think if I can find a good engine bay picture it will make sense.

J
jeffg is offline   Reply With Quote
Old 03-26-2003, 02:16 PM   #13
Legacy777
Scooby Guru
 
Member#: 4800
Join Date: Mar 2001
Chapter/Region: TXIC
Location: Houston, Tx
Vehicle:
1990 Legacy & 97 OBS
AWD 6MT EJ22T AWIC Swap

Default

Let me know if you can borrow a gauge or not.

Here's my hypothesis......with an intake you create a freer flowing intake system. At idle, throttle plate is closed....so that won't matter much what you have, so vacuum should remain the same no matter where you tie into the manifold.

At light throttle with the intake on, you have more air flow....especially in the main chamber where you've hooked the fpr line up to. This could produce more vacuum then at this particular point, compared to at the no. 3 intake runner.

I guess if you wanted to test this theory, you'd have to put the stock air box & crap back on......unless someone with a stock intake system and same MY car can take vacuum readings at the same two points.

Josh
Legacy777 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale: DEFI BF AMBER IMPERIAL fuel pressure and oil pressure syoung0298 Interior/Dressup/Audio & Security 5 06-09-2008 01:12 PM
97 Sti Afterfiring and running rich - Please help bradsti Newbies & FAQs 9 04-16-2008 07:30 PM
BOV means MAF messing up and running rich? Eijin Factory 2.5L Turbo Powertrain 5 08-08-2007 02:33 AM
relieve fuel pressure without running engine? gatts Factory 2.0L Turbo Powertrain 4 05-30-2007 05:08 PM
First results: High fuel pressure, and... scootr Normally Aspirated with bolt-on Forced Induction Powertrain 12 11-24-2001 02:18 PM


All times are GMT -4. The time now is 11:05 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2014 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.