Welcome to the North American Subaru Impreza Owners Club Wednesday September 24, 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 > Pre-2002 Factory Turbo 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 08-06-2012, 07:40 PM   #1
Merko
Scooby Newbie
 
Member#: 317488
Join Date: Apr 2012
Chapter/Region: International
Location: Adelaide, Australia
Vehicle:
1995 GC8C WRX import
White

Default 95 WRX - Removing over-boost fuel cut

Hi guys, I've got a 95 WRX, relevant mods being VF34, 3" turbo back exhaust, Walbro fuel pump and Z4 ECU (15.65psi fuel cut). A couple of months ago I raised boost to about 16psi with my MBC and the car would hit fuel cut at about 4500-5000rpm at WOT, which was when it would hit the 15.65psi fuel cut. We fixed this by tricking the MAP sensor and putting a one-way valve into the air hose for it so that it would only detect vacuum but no boost. This has worked perfectly for the past month or 2, but now it's suddenly hitting fuel cut again... and I can't figure out why! I've swapped that one-way valve for a brand new one to see if it just broke, but it's still happening. I've reset the ECU in the hopes that might do something but it hasn't. I have a spare MAP sensor so I'll try putting that in next. It's just weird that it was fine for this long with the one-way valve trick and now suddenly it's not :/

Is there anything else that controls fuel cut from overboost apart from the MAP sensor? Is it possible to just run no MAP sensor? Any other ideas?

Thanks
* Registered users of the site do not see these ads.

Last edited by Merko; 08-06-2012 at 07:45 PM.
Merko is offline   Reply With Quote
Old 08-07-2012, 12:17 AM   #2
RallySport Direct
NASIOC Storefront Vendor
 
Member#: 33174
Join Date: Feb 2003
Chapter/Region: RMIC
Location: Salt Lake City Utah
Vehicle:
We are Open Late!
888-457-2559 Every day!

Default

There are a few Fuel cut Defenders on the market. I ran the HKS "Fuel cut defencer" on my old EJ20G's awhile back and they worked perfectly

Hope this helps.
Thanks,
Rick
RallySport Direct is offline   Reply With Quote
Old 08-07-2012, 12:30 AM   #3
Merko
Scooby Newbie
 
Member#: 317488
Join Date: Apr 2012
Chapter/Region: International
Location: Adelaide, Australia
Vehicle:
1995 GC8C WRX import
White

Default

Yeah I was looking at the HKS unit but was hoping to avoid one altogether as my setup has worked and should still be working. But might end up going down that road. Where do you wire the defencer in? The MAP sensor wires or some wires at the ECU?

Thanks
Merko is offline   Reply With Quote
Old 08-07-2012, 09:37 AM   #4
pmugabi
Scooby Newbie
 
Member#: 280926
Join Date: Apr 2011
Default

Maybe the one way valve is leaking?

I used a similar setup for a few months at one time and it worked perfectly. Although it was not a one way valve, it was simply a T inline with the MAP sensor with one side left to the atmosphere (I know unmetered air etc, but it worked fine).

Another option is to put the 97+ MAP sensor, which is what I'm using now, by default it will cut boost at 1.5bar. It has a different electrical socket, so there is a bit of re-wiring to do.
pmugabi is offline   Reply With Quote
Old 08-07-2012, 12:53 PM   #5
TommyAtomic
Scooby Newbie
 
Member#: 257043
Join Date: Sep 2010
Chapter/Region: VIC
Location: Vancouver BC
Vehicle:
1993 JDM WRX Wagon
Black

Default

Quote:
Originally Posted by pmugabi View Post
Maybe the one way valve is leaking?

I used a similar setup for a few months at one time and it worked perfectly. Although it was not a one way valve, it was simply a T inline with the MAP sensor with one side left to the atmosphere (I know unmetered air etc, but it worked fine).

Another option is to put the 97+ MAP sensor, which is what I'm using now, by default it will cut boost at 1.5bar. It has a different electrical socket, so there is a bit of re-wiring to do.
If the valve was leaking I would think replacing it would have done the trick.

As to the 97+ MAP sensor. I would think that using Sensor that max's out at a higher value would require the ecu to have a new or rewritten table of MAP sensor values in the same way that a giant MAF sensor cannot simply be dropped in without a new tune that correctly interprets MAF values from a sensor with a higher max value.

As to the OP question, Do you have any datalogs with MAP sensor readings from before and now?
Is it possible that you have a vacuum leak somwhere else that is effecting the functionality of your one way valve. I dont think the ECU would typically let something doesnt run for months and stop working. If the ECU somehow relearned its usually in 2 weeks not 2 months.
TommyAtomic is offline   Reply With Quote
Old 08-07-2012, 01:19 PM   #6
Matt Monson
Scooby Guru
 
Member#: 832
Join Date: Jan 2000
Chapter/Region: RMIC
Location: Teh Ghetto Garage, CO
Vehicle:
99 2.5RS, '85 911
'73 914 and 2012 BRZ

Default

Over on Legacy Central, there is a sticky on how to make your own FCD. The one they describe there will work on an EJ20G just as it works on an Ej22T.
Matt Monson is offline   Reply With Quote
Old 08-07-2012, 06:43 PM   #7
Merko
Scooby Newbie
 
Member#: 317488
Join Date: Apr 2012
Chapter/Region: International
Location: Adelaide, Australia
Vehicle:
1995 GC8C WRX import
White

Default

I've checked for vacuum leaks and can't see any. I am stumped as to why it's suddenly started cutting again. I don't see how it's possible if the MAP isn't getting the pressure! And it's definitely boost cut because if I drop the boost a few PSI it will boost perfectly. Maybe the MAP is faulty? I'm still going to put my spare on there and see what that does.

But anyway, I bit the bullet and bought a HKS fuel cut defencer off eBay for $60. Hopefully that fixes it, or at least it'll tell me the problem is somewhere else.
Merko 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


All times are GMT -4. The time now is 12:54 AM.


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.