JDM GC8 - O2 sensor & rough idle question

bluegc8
Learner Driver
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JDM GC8 - O2 sensor & rough idle question

Postby bluegc8 » Mon Jul 24, 2017 9:58 am

First post after searching, searching and reading.

Firstly let me introduce the car. Purchased a couple of months back - a 1997 EJ20K Japanese import.
It has mild modifications like, TMIC, EL Headers, 3" exhaust, bigger turbo, 1000cc injectors and a tuned Apexi PowerFC

The car runs sweet. Plenty enough go for me, even at gate pressure. She runs fine until it warms up or sits in traffic, then the car would start to idle hunt.
Now I've been searching and reading up on this from IACV to AF sensors to doing upper head cleaning etc etc..

One thing I have notice consistently with the car is that the O2 sensor reading on the PowerFC commander.
Usually starts at about .20v and slowly creeps up as the car gets warmer. It drops and cycles through whilst driving and typically even goes down to 0.00v at spirited driving but quickly comes up to .20v - 0.40v. Car runs sweet.

Although at times during traffic I would see this creep up and almost every time it hits about .60v its starts to idle hunt. Car wants to shut off it actually did a couple of times.
The car would run rough during this time and I clear clear this up by giving the engine a few revs but usually mild boost a few times and the O2 would read back to about .30v - .40v and she is sweet again.

At time I've shut off the car to pay for petrol only to come back and the O2 would read about 0.70v - 0.80v and the car is idle hunting again. She runs rough - until I give it a boot a couple of times then until the O2 sensor reading would read 0.30v - 0.40v.

Its consistent every time.

O2 related issue or just coincidence ?
PowerFC Tunning Issues ?
I've read elsewhere non GC8 related threads where stuck EGR valve could be an issue ?

Any feedback would be much appreciated.
THANKS !!!

Lovin the GC8 !
Last edited by bluegc8 on Thu Jul 27, 2017 11:24 am, edited 1 time in total.

mv75
WRX STi Driver
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Location: Brisbane Northside.

Re: JDM GC8 - O2 sensor & rough iddle question

Postby mv75 » Mon Jul 24, 2017 1:19 pm

0.00 - full lean afr 20:1
0.45 - about stoich, afr 14.1:1
0.9 = rich. afr 10:1

Take that as you will.

It's in open loop from cold. Goes into closed loop when you hit a certain coolant temp, and you get sheet performance. Replacing the o2 is what looks like the go on paper here.

bluegc8
Learner Driver
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Joined: Mon Jul 24, 2017 9:40 am

Re: JDM GC8 - O2 sensor & rough iddle question

Postby bluegc8 » Wed Jul 26, 2017 10:19 am

thanks for the feedback mate !!!

its in the 0.45 - 0.50 when it starts to go funny. I'm assuming this is when it goes to closed loop.
it runs crap until i hit likt 3500rpm-4000rpm when it goes open loop and the runs fine. a few of this brings the O2 reading back down to the 0.20v - 0.3v. Then if i'm stuck in traffic this creeps up and up and up and starts to idle hunt when i get to the 0.50v

I turned off O2 Feedback on the PowerFC. From what i've read this will keep it in open loop. I just wanted to see.
i've see O2 reading up to 0.90v and the car runs and idles fine. no hesitation or idle hunting.

Is it potentially tune at closed loop ? if that can even be done - my apologies as I am new to tuning.
Or bad O2.
Stuck in traffic today and the O2 reading just stayed on 0.90v

Thanks

mv75
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Location: Brisbane Northside.

Re: JDM GC8 - O2 sensor & rough iddle question

Postby mv75 » Wed Jul 26, 2017 5:39 pm

Running rich all the time it'll run great, but increased risk of cylinder wall wash.

You could tune it to run like crap, but it's not consistent, if the tune was bad it would logically run bad the entire time. Replace the o2 sensor. On a car that old, don't be afraid to replace sensors. Remember this is still an internet diagnoses, it all points at the sensor for now.

ryano
Impreza WRX Driver
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Re: JDM GC8 - O2 sensor & rough iddle question

Postby ryano » Wed Jul 26, 2017 7:04 pm

just remember if you decide to tweak the idle map in the first few cells the power fc will require an idle relearn from memory any cell 4 across and 3 down, fuelling or timing will mess things up unless the relearn is done

bluegc8
Learner Driver
Posts: 6
Joined: Mon Jul 24, 2017 9:40 am

Re: JDM GC8 - O2 sensor & rough iddle question

Postby bluegc8 » Thu Jul 27, 2017 10:53 am

Thanks guys.
I'm not too keen on messing around with the maps. not confident enough in this yet.

I'm running O2 F/B Off just for the interim. Until I get another O2 sensor.
Car is running great and so far Fuel consumption is the same, if not a bit better - which is wierd.

Whats the go with Narrow Band and Wide Band O2. I'm still reading up on this but have been told I should get wide band since i am replacing it anyways.

Thanks

ryano
Impreza WRX Driver
Posts: 270
Joined: Thu Aug 19, 2010 9:12 pm

Re: JDM GC8 - O2 sensor & rough iddle question

Postby ryano » Thu Jul 27, 2017 11:05 am

the wide band won't be the same range so won't work with the power fc I'm pretty sure, if it was me i would get a narrow range for the power fc and a wide range with gauge to monitor

bluegc8
Learner Driver
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Joined: Mon Jul 24, 2017 9:40 am

Re: JDM GC8 - O2 sensor & rough iddle question

Postby bluegc8 » Thu Jul 27, 2017 11:22 am

oh ok. Thanks.

With regards to O2 Sensors - OEM ?
any recommendations

thanks !

ryano
Impreza WRX Driver
Posts: 270
Joined: Thu Aug 19, 2010 9:12 pm

Re: JDM GC8 - O2 sensor & rough idle question

Postby ryano » Thu Jul 27, 2017 3:43 pm

OEM would be best but might be expensive, i put an after market one in and its fine and has been for 100,000km now but its always a gamble. look on eBay

bluegc8
Learner Driver
Posts: 6
Joined: Mon Jul 24, 2017 9:40 am

Re: JDM GC8 - O2 sensor & rough idle question

Postby bluegc8 » Fri Jul 28, 2017 1:09 pm

you wouldn't happen to have a manufacturer and part number for the O2 you used ?
thanks

been a couple of days and car has been running so sweet. Fuel consumption is about the same. I don't see a difference.
although the car is on the rich side. 14L/100km - normal driving w very occasional boost.

once i get a new sensor, i will want to get her tuned again.
last tune was a couple of years back, but prev owner have mentioned she runs rich.

ryano
Impreza WRX Driver
Posts: 270
Joined: Thu Aug 19, 2010 9:12 pm

Re: JDM GC8 - O2 sensor & rough idle question

Postby ryano » Fri Jul 28, 2017 4:38 pm

bluegc8 wrote:you wouldn't happen to have a manufacturer and part number for the O2 you used ?
thanks

been a couple of days and car has been running so sweet. Fuel consumption is about the same. I don't see a difference.
although the car is on the rich side. 14L/100km - normal driving w very occasional boost.

once i get a new sensor, i will want to get her tuned again.
last tune was a couple of years back, but prev owner have mentioned she runs rich.


sorry it was years ago so not sure brand or number

mv75
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Location: Brisbane Northside.

Re: JDM GC8 - O2 sensor & rough idle question

Postby mv75 » Fri Jul 28, 2017 8:09 pm

http://www.ebay.com.au/itm/New-Genuine- ... 1c2caea495

I had this on my 2000 gc8. It's up to you if it fits your car. I also had a pec one from them too, wasn't that great like the walker was.

Was funny, while I was at subievolution today, Russ got a call for an o2 replacement. :)

bluegc8
Learner Driver
Posts: 6
Joined: Mon Jul 24, 2017 9:40 am

Re: JDM GC8 - O2 sensor & rough idle question

Postby bluegc8 » Wed Aug 02, 2017 3:29 pm

after a tank or so of fuel, running open loop - ignoring the O2, I'm getting better kms.
Ive been getting 300s on a tank. It is running rich.
Yesterday i had 340 and light hadn't turned on.
Filled up anyways.

I am going to get O2 and have the car tuned.

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