ive seen a couple of guys here saying that their oxygen sensor in the 3rd gen can give problems - whats the symptoms?
is it something to do with putting on extractors?
ive noticed recently my car seems to lack power / torque.. but im thinking it could also be a blocked CAT - since there seems to be a rattle when its cold...
any ideas on how to test / diagnose this?!
Cheers,
GuRu!

You can simply unplug your o2 sensor to test it, although it maybe masking some other problem.

To unplug it pull the console carpet down in the passenger foot well and remove the foot plate. The plug should be under the ECU, its got 4 wires and goes under the car thru a grommet.

ive seen a couple of guys here saying that their oxygen sensor in the 3rd gen can give problems - whats the symptoms?
Cheers,
GuRu!
I've had problems with a bad sulphury smelling exhaust, which some out there think might be due to a faulty O2 sensor, but the local Mitsi dealer reckoned it was the CAT, which they have replaced. The smell is still there at times, and when it is, power is down :shock:, and fuel consumption is up :mad:. I am thinking it could be the O2 sensor faulty, making it run rich. Anyone out there know if the MAF sensor can be faulty, causing similar symptoms?? I am going slowly mad with this problem, as when my ride runs well it canes:badgrin: I would like it to go this well all the time. :cool: Guru and I would like to know more!

Guru and StevoGSR have you tried to get the fault codes from your ECU? they should be able to tell you what sensor is playing up. Alternativly wip out the sensors and go down to the nearest Petroject or any EFI or bosch repairer and have them tested.

Guru take out your cat and go for a drive and see if it helps. you can also look into it to see if it has colapsed. Its amazing how bad it can make a car run, a mates soarer wouldn't boost past 4psi until he took it out and ran it, all was fixed.

something funny: GTI-r and the tt soarers have stickers and notes in the handbook not to park in long grass after highway or sustained heavy driving as the cat gets so hot its able to start a fire :redface:

Im having exactly the same problems and have just been advised to disconnect the O2 sensor as well and try that.

I know it is not the cat as i have replaced that.

Can someone who has disconnected or replaced the O2 sensor help out to see if these are symptoms of that and if it fixed the problem.

I replaced mine. The symptoms I experienced were rough accelaration at partial throttle. But good acceleration at near full and full throttle.

The effects of the oxy sensor will only be felt whilst the ems is in closed loop.

Best bet is to test for stored diagnostic codes as turbo_charade stated. Very easy to do and you don't have to pull your car apart or get your hands dirty. The procedure is as follows.

1. Firstly be sure your battery is nice and charged. Engine at operating temp and trans in Park or Neutral. If battery has recently been D/C then any stored codes will have been erased.
2. Best to make sure all accesories are off, stereo, head lights etc.
3. Turn the ignition switch to the 'ON' position but do not start the car.
4. (Refer to included pic) Ground terminal number one on connector located under drivers side dash, up close to the centre console and dash plastic that sits closest to your left leg in normal driving position, have a look around and you'll be able to see it. The best place I've found to ground this terminal to, depending on the length of your wire, is either the bolt holding the drivers seat down (make sure bolt is nice and clean and you can see bare metal) or the metal of the centre console, you just need to pull the carpet down a little to expose the metal.
5. As soon as this terminal is grounded properly with the ignition 'ON', the check engine light will start flashing, 9 consecutive quick flashes means everything is normal. If you have a busted oxygen sensor you will get 1 long flash then 1 short flash. Depending on how many codes are stored, they will keep going over and over with a short break between codes, until the terminal is no longer grounded.

And thats pretty much it, with out me typing too much more. After you replace a broken sensor be sure to D/C battery to cancel to old stored trouble code.

Trouble codes will only be reported if the oxy sensor is operating outside its normal readings.

If its slightly off ... then no error codes will come up ... but the car will accelerate like a bucket of the proverbial!! ;) (At small throttle changes ... full throttle and the oxy goes full rich anyway!!)

Trouble codes will only be reported if the oxy sensor is operating outside its normal readings.

If its slightly off ... then no error codes will come up ... but the car will accelerate like a bucket of the proverbial!! ;) (At small throttle changes ... full throttle and the oxy goes full rich anyway!!)

Interesting, I never knew that. Still though its not hard to check and doesnt take long, so why not give it a go if it hasn't been done already.

Yeah i will definately have a look for any fault codes - will let you know how i go..
im tending to think that the values could just be out a bit - but i think its the CAT now after giving it a bit of stick at WOT she definately feels laggier - if the OXY sensor doesnt do anything on WOT then im guessing its some other issue..
:rant:

*Edit - Magna left my PC logged in as him - this is actually GuRu! logging out now!*

If u r gonna replace your cat.

Go a hi flowed one. They aren't as expensive as you would think, about $200-$300, about the same as a stock replacement.

in my case the oxy sensor was stuffed but when running the diagnostic both through the computer and grounding the the number 1 terminal nothing came up no error coes at all plus i checked it with the multimeter and it was with in all specified ranges, very strange but once i replaced it was all good again

Clarion MAgna,

How did you know it was stuffed ?? What were the symptoms ??

bascially it happnened not too long after i got my extractors installed, the problem started slowly and gradually got worse, what it would do was when i accelerated normally and the revs we reach 2500-3000rpm it would cut out almost like it couldnt get any fuel and if i didnt let off the accelerator the car would backfire which sounded like a small nock, the constant backfiring eventually killed the airflow meter we we ran the diagnosis test the code for airflow meter came up so we thought that was why the car was running crap so we replaced it, it fixed it for a few days and then the problem came back.

after speaking to some one else who had just installed extractors and had the same problem i was convinced it was the oxygen sensor so i replaced it and the car was perfect after that, was very strange as to why the diagnosis test did pick up on it

Before it got that worse, did you notice a lack of power from 2000-3000 rpm? the problem that i have is that say your cruising at 60kph in 4th, and you wanna speed up to say 75kph, you put your foot down about an inch but the car doesnt seem to wanna move or accelerate unless you drop a gear and bring it over 3000rpm?
thats what mine is doing..
there also seems to be a lack of power down low even when you put your foot flat..
GuRu

i didnt notice any power loss, the car was basically running like a dog, if i were crusing at 60 and put my foot down a bit the revs would go up a bit and then the engine would pretty much cut out unless i let off the accelrator if i kept on the accelerator it would just backfire, the only way to try and avoid the cutting out was to put the accelerator flat to the floor e.g stoped then flat to the floor the car would rev fine to about 2000-2500 then start to hesitate sound like it cant get fuel then get to about 3000-3300 and all of a sudden the power would just snap back on jolting the car was very strange

i think basically the oxy sensor was sending the wrong signals to computer and therefore making the wrong mixtures

in your case it dosent sound like a oxy sensor best do a diagnosis test and see if any thing comes up, if nothing maybe the car could be in need of a bit of a tune

If you had your foot flat to the floor, the oxy sensor is ignored (out of closed loop). There must be something else wrong.

The only time the oxy sensor has an effect on mixtures is when in closed loop mode, where the EMS adjusts mixture based on the sensor. Once certain conditions occur ( e.g revs are over a certain amount, or throttle position is past like 40% or somewhere around there) the EMS reverts to using a mapped based mixture control.

You can tell this occurs because when you put you boot into it the oxy sensor just goes FULL rich. So the computer can't possibly be using it.

Unless of course it is registering the fact that its not full rich ... and trying to adjust for this. Now you have me thinking.

Might have to hook up the oxy sensor to a switch and play around with it.

Is it true that if we feel that we have a problem with the Oxygen Sensor then we can just disconnect it and drive the car around like that with the sensor disconnected ??

You can disconnect it with no side effects other than an increase in fuel consumption (oh and more emissions ... but as if that bothers anybody here ;))

If the oxy is disconnected the EMS reverts to maps only and never enters closed loop. When I disconnected mine (to test it of course) ... no check engine appeared (didn't bother checking for fault codes as I reset the EMS after reconnecting anyway).

well all i can say is that after replacing it the car ran perfect, also when starting inthe morning to the let the car warm up after about 2-3 minutes the car would start to hunt getting worse and worse to the point where it would stall

i would have thought disconnecting the sensor would have made things worse, i could have avoided killing my engine in the morning just trying to drive:cry:

The only issue i may have with disconnecting the Oxygen Sensor is that i have a Unichip and that if the computer reverts back to standard maps, my Unichip becomes useless and i lose a lot of power ???

Could that be true ??

I bet you at low rpm etc the unichip is not doing much anyway. It can't possibly be doing anything when the EMS is in closed loop. If it is, the EMS will just be adjusting it out anyway.

If the Unichip controlls the spark timing, this will still be to your advantage giving you extra power and is unaffected by open or closed loop mode. Chances are also that the Unichip has been pre-tuned with better fuel maps (than factory) while at wide throttle openings and thus in open loop mode.
This is the theory anyway, I don't actually have a Unichip so I can't prove thats what it does.
The oxy sensor is important so don't disconnect it except as a test to see what results it has.
Closed loop mode is still probably controlled by the existing factory ECU.

Trouble codes will only be reported if the oxy sensor is operating outside its normal readings.

If its slightly off ... then no error codes will come up ... but the car will accelerate like a bucket of the proverbial!! ;) (At small throttle changes ... full throttle and the oxy goes full rich anyway!!)

dam right, a problem with oxy sensor causing laggy acceleration and cruising below 3000rpm after getting extractors on drove me nuts for months, i took it to mitsubishi and asked if it was oxy sensor, they said no bec error codes ok. when i disconnected it the problem disappeared, then got it replaced.

Seem to be a few people having problems with oxy sensor or poor running after fitting extractors. Think I read that care must be taken when removing the sensor from the old exhaust pipe and replacing it in the extractor pipe.

The question should be asked - has anyone who has replaced their oxy sensor after fitting extractors had the sensor fail a second time?

It sounds like some exhaust shops are just busting the sensor when they take it out...?

a top mechanic told nme he never leaves them exposed hanging out of cars, always puts them in a bag and tapes it up. But its the fumes from the gasket sealant if the wrong ones used that kills the sensor with the extractors :cool:

Yeah i made sure that when i got my extractors fitted we used the correct sealant so it didnt kill the oxy sensor - bad luck perhaps? i wonder if something coming from the HPC coating on the pacemakers is causing a problem with the mitsu oxy sensors?
:redface:

Expensive parts to replace too. I got quoted $270 from Mitsubishi today to just supply the Oxygen Sensor.

Expensive parts to replace too. I got quoted $270 from Mitsubishi today to just supply the Oxygen Sensor.
Repco have suitable ones, usually in stock too! (makes you wonder how often they really fail given they are a stock item and all!!!)

About $180

holy crap $270 for O2 sensor?!?!?! wow.... $180 is more like it. We do them at $165 delivered for a TE-TH or $60 for a TN-TS.
:cool:

Thanks for that Tooslow.

I might check out the suitability for the Ralliart with Repco.

Thing is, i like to try and keep using genuine parts on the Ralliart.