Welcome to the North American Subaru Impreza Owners Club Saturday August 23, 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 > Factory 2.0L 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 12-15-2002, 12:04 AM   #1
toobluewrx
Scooby Newbie
 
Member#: 4911
Join Date: Mar 2001
Location: Mauldin, SC, USA
Vehicle:
2002 Impreza WRX
Blue

Lightbulb Part throttle hesitation mod....

I think I've found an inexpensive fix to minimize the hesitation that occurs under part throttle & light boost on some WRXs. My mods are uppipe, downpipe, muffler, and TXS Stage 2 Unichip.

Thinking that the hesitation is caused by the fuel mixture being slightly too lean while in closed loop control, I researched how to make the mixture richer. In closed loop mode, the ECU uses feedback from the front O2 sensor to control the air/fuel ratio. So if I could alter the signal from this sensor to indicate the A/F ratio was leaner than actual, the ECU would add fuel to compensate.

The front O2 sensor produces a milliamp signal proportional to the A/F ratio. The signal changes polarity as the A/F ratio changes from lean to rich. By externally adding a milliamp signal of the right polarity, I could shift the A/F ratio being reported by the sensor.

The sensor has four wires, two for a heater element, and two for the A/F signal. I used a 10K resistor between the +12V lead for the heater element and the + connection of the A/F signal. This provides ~1 milliamp of signal in the lean direction. The ECU compensates for this during closed loop by adding more fuel.

The connector for the front O2 sensor is located beneath the cover for the boost control solenoid. There is a vertical stack of three connectors here. The top connector is for the O2 sensor. On the female side of this plug, using a pair of needle nose pliers, push the resistor leads about an inch into the top two holes where the wires exit. With the key switch on, use a voltmeter to verify you have 12 volts on one resistor lead, and about 3.8 volts on the other.

Here is a simple diagram of the connector with the resistor installed:
Code:
   /\/\/\
  |     |
+-|-----|-+
| O     O |
|         |
| O     O |
+---------+
This mod has virtually eliminated the hesitation. I've had it in for about two weeks. The only downside that I've noticed is a drop of about 1 mpg in mileage.

Those of you with hesitation may want to give this a try. Post your results.

AB
* Registered users of the site do not see these ads.
toobluewrx is offline   Reply With Quote
Old 12-15-2002, 03:19 PM   #2
nhluhr
John Wayne Toilet Paper
Moderator
 
Member#: 7327
Join Date: Jun 2001
Chapter/Region: NWIC
Location: Seattle, WA
Vehicle:
2008 Mazdaspeed3
2006 Wrangler Sport

Default

so you're telling me the current through the O2 sensor rises as the sensor reads leaner and leaner? And adding the 10kohm resistor across the two signal leads in effect presents LESS resistance to the entire circuit (resistors in parallel do not add more resistance)...

is that right?
nhluhr is offline   Reply With Quote
Old 12-15-2002, 04:08 PM   #3
inthememof911
Scooby Newbie
 
Member#: 14055
Join Date: Jan 2002
Location: subyland
Vehicle:
2013 Mustang GT
-RIP bug eye-

Default

same confution as nhlur. Please elaborate a little more.
inthememof911 is offline   Reply With Quote
Old 12-16-2002, 12:02 AM   #4
toobluewrx
Scooby Newbie
 
Member#: 4911
Join Date: Mar 2001
Location: Mauldin, SC, USA
Vehicle:
2002 Impreza WRX
Blue

Default

nhluhr & inthememof911 - The A/F sensor's output is a current signal. This current is produced by an electrochemical reaction occuring in the sensor (like a battery) when the sensing element is heated to ~700 degrees C (by the heater circuit). The sensor produces zero current at an A/F ratio of 14.5, an increasing positive current for lean mixtures (>14.5), and an increasing negative current for rich mixtures (<14.5).

For the A/F sensor to work, the ECU must provide a bias voltage across the sensor of ~0.3V. It does this by holding one side of the sensor at 3.8V, and the other side at 3.5V. What I am doing is using the +12V supply (through the 10K resistor) to provide a current source to sum with the current signal produced by the A/F sensor.

The circuit that measures this current in the ECU thinks the current comes strictly from the A/F sensor. With the engine running, the battery voltage is about 14V and the + sensor terminal is about 3.8V (so there is ~ 10V across the 10k resistor which means there will be ~ 1 milliamp flowing). This current sums into the signal from the A/F sensor.

Use this link to learn more about this type of A/F sensor:
http://jon.in.ct.home.att.net/SAE970843.PDF
Credit to "Jon [in CT]" (who posts here frequently) for the link.

There is also evidence that the pressure in the exhaust manifold changes the calibration of the A/F signal. See this page: http://forums.nasioc.com/forums/show...hreadid=269143

Maybe this is the real reason we're having this poor driveability at low boost in closed loop. We've changed our exhaust system (uppipe, catless downpipe, low restriction muffler) which has significantly reduced the exhaust back pressure. Since the ECU can't measure the back-pressure, it must have look up tables to correct the signal from the A/F sensor. Since the back pressure with the revised exhaust is now less, the ECU is calculating an incorrect A/F ratio (too lean).

Comments?
toobluewrx is offline   Reply With Quote
Old 12-16-2002, 12:53 AM   #5
nhluhr
John Wayne Toilet Paper
Moderator
 
Member#: 7327
Join Date: Jun 2001
Chapter/Region: NWIC
Location: Seattle, WA
Vehicle:
2008 Mazdaspeed3
2006 Wrangler Sport

Default

it seems to me it would be possible to have a pressure sensor in the exhaust near the O2 sensor and you would then have a small circuit that scaled the O2 signal, as necessary, with respect to the pressure in the exhaust at that point.
nhluhr is offline   Reply With Quote
Old 12-16-2002, 01:12 AM   #6
koloumb
Scooby Newbie
 
Member#: 28268
Join Date: Oct 2002
Chapter/Region: NWIC
Location: Oregon
Vehicle:
2002 WRX Sedan
WRB

Default

Wouldn't an ECU reflash take care of this? My understanding of reflashing the ECU is the tuner can alter settings to adjust for modifications done to your engine/exhaust.

_0wen_
koloumb is offline   Reply With Quote
Old 12-20-2002, 11:05 PM   #7
toobluewrx
Scooby Newbie
 
Member#: 4911
Join Date: Mar 2001
Location: Mauldin, SC, USA
Vehicle:
2002 Impreza WRX
Blue

Default

Anyone else tried the resistor mod yet?
toobluewrx is offline   Reply With Quote
Old 12-20-2002, 11:17 PM   #8
recursian
Scooby Newbie
 
Member#: 9976
Join Date: Sep 2001
Location: Atlanta, GA
Vehicle:
2003 Subaru WRX
Blue

Default

Are you talking about poor closed loop performance during boost or non-boost conditions?
recursian is offline   Reply With Quote
Old 12-20-2002, 11:28 PM   #9
toobluewrx
Scooby Newbie
 
Member#: 4911
Join Date: Mar 2001
Location: Mauldin, SC, USA
Vehicle:
2002 Impreza WRX
Blue

Default

recursian
Quote:
Are you talking about poor closed loop performance during boost or non-boost conditions?
During boost (20-50% throttle & 2-7psi boost).
toobluewrx is offline   Reply With Quote
Old 12-20-2002, 11:42 PM   #10
recursian
Scooby Newbie
 
Member#: 9976
Join Date: Sep 2001
Location: Atlanta, GA
Vehicle:
2003 Subaru WRX
Blue

Default

That's what I thought. It should be illegal for a person to make a turbo car that runs closed loop during boost. It's all politics. I'm concerned that the heater power isn't regulated. Also, if your mod is working, you are sacrificing fuel economy during the majority of the time you are driving. If you took a 300 mile trip on the highway and never ran boost, you would have blown some fuel. The best thing to do is make the computer go open loop. You can make your own circuit to do this as I did on my Honda or you can buy the Vishnu EMI Adapter. Yes, I talk about the EMI Adapter a lot, but it's because the thing works. Most people don't understand the importance of it. Anyway, the other thing you may consider is making your additional current flow only when under boost. You can get a 1 psi Hobbs switch and wire a relay or make a simple circuit with a comparator on the MAP sensor circuit. I would get a 5 volt regulator, comparator and trim pot and do it that way. Oh yeah, you might need an analog switch or cheap multiplexer too.
recursian is offline   Reply With Quote
Old 12-21-2002, 01:02 AM   #11
Vishnu Performance
Vendor
 
Member#: 14494
Join Date: Jan 2002
Location: SF Bay Area, California
Vehicle:
WRX Porsche 996
blue & black

Default

Quote:
Originally posted by recursian
You can make your own circuit to do this as I did on my Honda or you can buy the Vishnu EMI Adapter. Yes, I talk about the EMI Adapter a lot, but it's because the thing works. Most people don't understand the importance of it.
Judging by the demand we're seeing, I think enough people do Certainly keeps us and our fabrication house busy. In fact, I just spent two hours this evening programming 75 of them! Time to go to sleep...

Cheers,
shiv
Vishnu Performance is offline   Reply With Quote
Old 12-31-2002, 01:56 AM   #12
Lit4
Scooby Newbie
 
Member#: 23758
Join Date: Aug 2002
Location: Delaware/Cali
Vehicle:
SOLD MY03 REX SILV
miss the dang SCOOBYSPORT

Default

so has anybody else tried this? is it safe?
Lit4 is offline   Reply With Quote
Old 12-31-2002, 07:08 AM   #13
recursian
Scooby Newbie
 
Member#: 9976
Join Date: Sep 2001
Location: Atlanta, GA
Vehicle:
2003 Subaru WRX
Blue

Default

So Shiv, you're flashing the Pic microcontroller? Are you doing the programming too? Are you open to requests to modify the code if we come up with viable additions?

Chris
recursian is offline   Reply With Quote
Old 12-31-2002, 08:15 AM   #14
IggDawg
Celebrity Guest Star
 
Member#: 10648
Join Date: Sep 2001
Chapter/Region: NESIC
Location: Sort of Boston, MA
Vehicle:
2002 Escort... D:
Mostly kind of white

Default

I've been getting some bucking/hesitation at part throttle and full boost with my MBC. I'm thinking this might help a lot. Only thing is, if I'm running rich at WOT already, won't this just make it worse?

-IggDawg
IggDawg is offline   Reply With Quote
Old 12-31-2002, 06:23 PM   #15
toobluewrx
Scooby Newbie
 
Member#: 4911
Join Date: Mar 2001
Location: Mauldin, SC, USA
Vehicle:
2002 Impreza WRX
Blue

Default

Quote:
I've been getting some bucking/hesitation at part throttle and full boost with my MBC. I'm thinking this might help a lot. Only thing is, if I'm running rich at WOT already, won't this just make it worse?
-IggDawg
IggDawg,

This mod only comes into play during closed loop operation (<50% throttle and < 4300 RPM). It will have no effect during WOT.

Go to Radio Shack and buy a pack of 5 resistors for $1. Try it and let us know if it works for you. This simple mod has made a night and day difference in the drivability of my car!

AB
toobluewrx is offline   Reply With Quote
Old 01-01-2003, 09:25 AM   #16
IggDawg
Celebrity Guest Star
 
Member#: 10648
Join Date: Sep 2001
Chapter/Region: NESIC
Location: Sort of Boston, MA
Vehicle:
2002 Escort... D:
Mostly kind of white

Default

Quote:
Originally posted by toobluewrx

IggDawg,

This mod only comes into play during closed loop operation (<50% throttle and < 4300 RPM). It will have no effect during WOT.

Go to Radio Shack and buy a pack of 5 resistors for $1. Try it and let us know if it works for you. This simple mod has made a night and day difference in the drivability of my car!

AB
As soon as I read "colsed loop" a big smile smeared across my face . I completely forgot that whole 02 sensor/closed loop thing. I skimmed 79 cents off petty cash yesterday when I was out getting lunch for everyone and snagged the resistors. that's the only question I had before I try this . I'll let you all know how it goes.

-IggDawg
IggDawg is offline   Reply With Quote
Old 01-01-2003, 10:24 AM   #17
Lit4
Scooby Newbie
 
Member#: 23758
Join Date: Aug 2002
Location: Delaware/Cali
Vehicle:
SOLD MY03 REX SILV
miss the dang SCOOBYSPORT

Default

Im no genius about this kinda thing so I'm still having second thoughts. There isn't anything that could go wrong after doing this mod?
Lit4 is offline   Reply With Quote
Old 01-01-2003, 12:16 PM   #18
djerickd
Scooby Guru
 
Member#: 3782
Join Date: Jan 2001
Chapter/Region: South East
Location: Tampa B*tch!
Vehicle:
02 WRX WFC#040
Clean on 19's

Default

Anyone else tried this??
djerickd is offline   Reply With Quote
Old 01-01-2003, 01:01 PM   #19
Chuck H
Scooby Specialist
 
Member#: 20442
Join Date: Jun 2002
Chapter/Region: NESIC
Location: Chelmsford, MA
Vehicle:
KTR tuned 2003 WRX
VF34 equipped, 270 whp

Default

I don't know enough about the Subaru ECU to really judge, but this doesn't seem like a very good idea. What you're doing is fooling the ECU so that it doesn't know the stoichometric a/f ratio (14.7:1) any more. That's going to affect a lot of other stuff, besides a stumble at it comes into boost at part throttle. You will be making the car run too rich the whole time it's in closed loop mode, even when not at boost. It will use more fuel, and probably damage the catalytic converters over time by dumping unburned gas into the exhaust.

I also don't know anything about Shiv's auxiliary electronics, but I would think that a circuit to trick the ECU into open loop mode at lower RPM would be a better solution.
Chuck H is offline   Reply With Quote
Old 01-01-2003, 06:12 PM   #20
sajohnson
Scooby Specialist
 
Member#: 6140
Join Date: Apr 2001
Chapter/Region: MAIC
Location: Middletown, MD, USA
Vehicle:
2002 WRX 5MT Sedan
WR Blue. Cobb Stage 2

Default

toobluewrx's mod seems fine to me. Other than the excess fuel consumtion, the price is right.

Ideally though, if you have the cash, an ECU reflash or aftermarket device from Vishnu or turboXS would be the way to go.
sajohnson is offline   Reply With Quote
Old 01-02-2003, 10:54 AM   #21
AndyHidley
Scooby Newbie
 
Member#: 1031
Join Date: Mar 2000
Location: PA, USA
Vehicle:
2002 WRX
Blue

Default

toobluewrx.. On the connector there are 4 wires, two black, one white, one blue. Which ones did you use?

Did you try any other value resistors than 10K? If so what were the effects of more or less resistance. Other than making it richer or leaner... What I'm gettin at is using your method how much richer should it really be so it does not hesitate?

Also, Is the O2 sensor heated electrically ALL the time? Or only during the first few mins of operation? If only a few mins then the 12V would terminate...............

Last edited by AndyHidley; 01-02-2003 at 11:00 AM.
AndyHidley is offline   Reply With Quote
Old 01-02-2003, 11:10 AM   #22
Lit4
Scooby Newbie
 
Member#: 23758
Join Date: Aug 2002
Location: Delaware/Cali
Vehicle:
SOLD MY03 REX SILV
miss the dang SCOOBYSPORT

Default

Any1 with an EGT gauge do this and see a change?
Lit4 is offline   Reply With Quote
Old 01-02-2003, 11:17 AM   #23
IggDawg
Celebrity Guest Star
 
Member#: 10648
Join Date: Sep 2001
Chapter/Region: NESIC
Location: Sort of Boston, MA
Vehicle:
2002 Escort... D:
Mostly kind of white

Default

I've got a legacy turbo, not a WRX. as a result, my front O2 sensor has 3 wires, not 4. any idea which ones I need to bridge? I went to try this out and saw I had a different setup. I'm getting a little tired of only being able to drive at 0-20% throttle or 80-100% throttle.

-IggDawg
IggDawg is offline   Reply With Quote
Old 01-02-2003, 09:43 PM   #24
toobluewrx
Scooby Newbie
 
Member#: 4911
Join Date: Mar 2001
Location: Mauldin, SC, USA
Vehicle:
2002 Impreza WRX
Blue

Default

Quote:
toobluewrx.. On the connector there are 4 wires, two black, one white, one blue. Which ones did you use?

Did you try any other value resistors than 10K? If so what were the effects of more or less resistance. Other than making it richer or leaner... What I'm gettin at is using your method how much richer should it really be so it does not hesitate?

Also, Is the O2 sensor heated electrically ALL the time? Or only during the first few mins of operation? If only a few mins then the 12V would terminate...............
AndyHidley,

I used the top black & white wires (actually the wires on the female connector that mate to the top black & white wires). The two black wires go to the heater, and the white and blue are the sensor output.

I started with a 100K resistor, and kept decreasing the value until I got a noticeable effect. I'm currently using a ~8K resistor (two 3.9K in series). I would estimate that with this resistor, the A/F ratio is ~ 13.5 to 1.

It seems that one side of the heater always has 12V applied (with the key switch on). The other side is being switched to ground (probably varying the duty cycle to control the temperature).

AB
toobluewrx is offline   Reply With Quote
Old 01-03-2003, 02:06 AM   #25
Lit4
Scooby Newbie
 
Member#: 23758
Join Date: Aug 2002
Location: Delaware/Cali
Vehicle:
SOLD MY03 REX SILV
miss the dang SCOOBYSPORT

Default

Is there any significance of a 10k over an 8k? Why did you change
Lit4 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
On/Off throttle hesitation, cured by ecu reset Draken Factory 2.5L Turbo Powertrain 15 09-29-2005 01:54 PM
Hesitation in part throttle MY03 Lancer3d Engine Management & Tuning 4 01-08-2005 09:29 AM
Part throttle hesitation with Ecutek? Equilibrium Tuning Factory 2.0L Turbo Powertrain 11 05-30-2003 06:13 PM
Part throttle hesitation merlot Factory 2.0L Turbo Powertrain 6 01-04-2003 09:13 PM
serious studdering when car lauches also throttle hesitation=>HELP AliBenn Normally Aspirated Powertrain 10 04-02-2001 08:46 PM


All times are GMT -4. The time now is 03:05 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.