Oxygen sensor issues - hesitation in closed loop

[dimin]

Took the car away for a decent trip this long weekend, did 450odd km. Ran it in open loop with O2 unplugged for first half of the trip, ran beautiful and smooth. Wasnt too bad on gas either, about 250km from full tank to half.

On return trip I plugged the factory o2 back in for the last 50km or so, seemed to be a lot less hesitant after driving for a bit. Still there but far less noticeable, strange. Also the AFR's were holding a bit more stable around the 14.7 mark, cycling between 14.3-15.1. Still hoping I can disconnect the o2 completely though and get it tuned purely in open loop. One thing I want to check is for any sign of exhaust leaks as EJ20T said, maybe there's a small one I havent noticed thats letting clean air in and throwing off the o2 readings. Might do a little more investigating tomorow. Did check for airleaks too, but I might double check that tomorow.

[Guest]

this is a sensor issue, have seen this many times - Genuine sensor time or bosch replacement unit ,

NOTHING ELSE seems to be up to the requirements of Subaru system

Your new O2 still has great output, but is technically "SLOW" -

Did some teswting about 5yrs ago and I have run a genuine in a test alongside a aftermarket at the same time

When in closed loop, and the voltage from the sensors is occillating up and down 0.2v to 0.8v

due to sensor aftermarket sensor output being slow, it is miss timed with the actual AFR

When the car is 0.2 the A/M sensor is showing 0.8 - so the ecu leans the mixture

Then it becomes so lean it richens up, as sensor is slow it is still showing lean so ecu increase's inrichment again - now going too rich

Replace sensor and all will be well

One other question, how are you reading AFR - wideband sensor? if so does the system give a simulated narrowband for ECU?

[WRXONP]

he said he tried the simulated o2 out put . still same problem. its ver7 yeah? has the o2 and the air fuel ration sensor in the manifold too ?

[gazzy2000]

i thought it was a v5/6..

did you reset the ECU when you unplug and replug the o2 in?

[WRXONP]

yeah i all ways reset my ecu. i had the same problem as above. my o2 sensor got damaged from removing and re fitting my down pipe so many times to make my new waste gate set up . i replaced my o2 and reset ecu and is fine now . i used Bosch o2 sensor

[gazzy2000]

so is his car a v5/6 or v7?

his sig says current v5

[Guest]

So O2 at top of down pipe if V5/6 and three wire narrowband

If it is running simulated voltage off wideband display then this will cause issues too

(Just read entire thread, -- refit ya old sensor if it worked ok)

[dimin]

V5 Sti is the car, 3 wire narrowband sensor in the downpipe. Ichi Ban your theory sounds on the money, I might try and find a proper Subaru factory one and try that. Unfortunately the old one I pulled out i damaged removing so cant refit it ! But never mind. Am going to Tauranga for work tomorow, might stop into the Pick a part there and see if there are any standard Subaru sensors I can grab and try.

Also been trawling through threads on O2 sensors and saw in one that QRAF had problems with a repco a/m sensor and changing to a geniune Suby one sorted the surging issues so keen to try a genuine one now ! Will update once Ive tried it if it has sorted the problem.

Also running the narrowband simulated output does make it worse, assuming the signal delay causes this. Oh and yes tried resetting the ECU plenty and hasnt made a difference unfortunately.

[gazzy2000]

the genuine subaru ones are bosch and are around $350-$400. bosch make the 3 wire univeral, if you know the right person you can get em for around $140-$180

i have used three of these, one of which was on my v3/4 STI that had hestiation probs like yours and it worked a treat, another was on my BH5 TT to ST conversion (essentially a v5/6)

heres the bosch 3 wire universal part number

[WRXONP]

strongs has the Bosch ones used for 60 buck with 6 month warranty

[gazzy2000]

 WRXONP said:

strongs has the Bosch ones used for 60 buck with 6 month warranty

if it were me i wouldnt buy second hand, o2's are meant to be changed around the same KMs as your cam belt, so really its money better spent towards a new one... IMO

[Guest]

 gazzy2000']

[quote name='WRXONP said:

strongs has the Bosch ones used for 60 buck with 6 month warranty

/quote]

if it were me i wouldnt buy second hand, o2's are meant to be changed around the same KMs as your cam belt, so really its money better spent towards a new one... IMO

+1 iv yet to replace mine.gave it a quick clean when i swapd my downpipe.

is one of the things on my list to change.not keen to pay 399 tho

[gazzy2000]

 sti8u']

[quote name='WRXONP said:

strongs has the Bosch ones used for 60 buck with 6 month warranty

/quote]

if it were me i wouldnt buy second hand, o2's are meant to be changed around the same KMs as your cam belt, so really its money better spent towards a new one... IMO

+1 iv yet to replace mine.gave it a quick clean when i swapd my downpipe.

is one of the things on my list to change.not keen to pay 399 tho

once again... bosch universal FTW ;D

less than half the price & have worked absolutely mint for me in the past

(they are still genuine bosch, prolly the same as OEM subaru part without the price tag)

[QRAF]

yeah it went away with genuine one but its come back so i'm not 100% sure if thats the issue mine ver5 wrx

to tell the truth its only ever started to have these issues after i did 946kms on that force 10 gas from gull i know now that it says on the subaru website not to use that gas for my car.

But i didn't know at the time so i'm thinking i've burnt something out?

[gazzy2000]

PM clubsub member robertsm for getting you an bosch universal o2 sensor for around $135.00, that is VERY cheap, genuine subaru will be $250+

(dunno about v7 on, they may use those ghay expensive o2s)

[Guest]

V7 runboth a 4 wire (AFR) and 3 wire (O2)

[WRXONP]

can't complain with a 6 month warranty though aye if it stuffs out i go get another one :-) . and i red in a brochure that gull force 10 can damage o2 sensors

[QRAF]

yeah i've replaced it already tho 1st one with a sti one same version 5 fixed it but it came back after the next tank replaced it with a bosch one which did the same thing it came back faster tho like 100kms later i reset the computer under the dash each time.

i'm thinking about taking it to a garage and letting him have a go at fixing it might be a easy fix.

I've also changed my afm, fuel filter, fuel pump cleaned my intake cleaner as said before.

[WRXONP]

ya fuel pick up sock not blocked ?

[QRAF]

 WRXONP said:

ya fuel pick up sock not blocked ?

thats a thought when i switched over pumps we didn't change that part ??? : got me thinking now i have done a lot of kms and i do run the tank dry now and again. ???

[Guest]

Re Fuel pump pick up, the fault would be worse with rpm/load if supply is restricted (unless DC % pump set up)

As in first post by Dimin - fault started afetr O2 replaced

[dimin]

So ive been playing round with the programmable output of the Innovate MTX-L, have found voltage settings that seem to make the closed loop fuelling behave somewhat. Have got it so it sits between 14.6 and 14.9 AFR, which is spot on what it should be really. Not sure how long before the ECU throws a code, if it does at all. So far its been running good, and the AFRs dont swing wildly all over the show, very stable.

Will see how it goes for the next week or so and if its fine like that it can stay that way !

May try another TPS in the meantime though, to see if it has any effect.

[Guest]

Have you set a "false" O2 reading to ECU?

[dimin]

Ive set it so that at 14.5 afr its 0.41V, at 15.3 afr its 0.49v, the ECU looks for it switching across the 0.45v value as far im aware ? So the hope was to the ecu its still functioning right. Dunno though, not sure how the software/code works in the ECU.

[Guest]

think you might encounter an issue when the ECU tries to correct fuel

Have you tried leaving it idling for 10min when warm and seeing what happens to AFR?