kill1308 Posted December 12, 2009 Share Posted December 12, 2009 (edited) Hi peeps, My car (96 BPU TT - double decat) has been smelling very very rich for quite some time. After the fuel consumption dropped below 200miles per tank I figured something might be up. The idle is also a little unstable at times and I seem to have lost a bit of performance (this is what the butt dyno tells me ). Would severe overfuelling cause a loss of performance, or am I probably imagining this? It's not drastic, just doesn't seem as quick as it used to. After reading a guide on how to check the O2 sensor on your car I decided to give it a whirl. Warmed the car up, got the fluke meter out and followed the instructions as per the guide on this site... Well the results were a fluctuation of voltage between 0.135v and 0.850v. It seems to be all over the shop... Reckon this is a buggered O2 sensor, or is the fact that it's not a solid figure between 0.8v-1.0v mean this is a red herring for overfuelling... or do we think it's knackered ? Thanks for any advice Edited December 12, 2009 by kill1308 (see edit history) Quote Link to comment Share on other sites More sharing options...
kill1308 Posted December 12, 2009 Author Share Posted December 12, 2009 Well I've been doing a bit more research into this and I'm still not sure whether or not to bite the bullet and get a new O2 sensor from Toyota... Quote Link to comment Share on other sites More sharing options...
Andy Blyth Posted December 12, 2009 Share Posted December 12, 2009 Would severe overfuelling cause a loss of performance, or am I probably imagining this? It's not drastic, just doesn't seem as quick as it used to. Overfuelling will hurt performance, but I strongly doubt your o2 sensor plays a role in this. It is not used to control fuelling when on boost with wide open throttle; the ecu will be in open loop mode. Well the results were a fluctuation of voltage between 0.135v and 0.850v. It seems to be all over the shop... That's the behaviour I would expect. The stock o2 sensor can only detect lean or rich, not in-between. This means that the stock ecu must constantly move from rich to lean and back to approximate stoich. a red herring for overfuelling Maybe. If you have been cruising off-boost lots and still getting less than 200 miles to the tank it could still be a bad o2 sensor. Could be something like a faulty MAP sensor or a sticky injector. Quote Link to comment Share on other sites More sharing options...
kill1308 Posted December 12, 2009 Author Share Posted December 12, 2009 Thanks for the reply Andy appreciate it, I might take the car to a Supra specialist somewhere then if it could be stuff other than the O2 sensor as I've not really got any way of testing anything else. I thought with the O2 sensor it was ideally supposed to hunt between 0.5v-0.7v rather than such a wide fluctuation like I'm getting? Quote Link to comment Share on other sites More sharing options...
Andy Blyth Posted December 12, 2009 Share Posted December 12, 2009 I thought with the O2 sensor it was ideally supposed to hunt between 0.5v-0.7v rather than such a wide fluctuation like I'm getting? The sensor should be fluctuating between approximately 0.15 V and 0.85 V. Here's a graph shamelessly stolen from stealth316.com: You can see that the voltage varies rapidly for a small change in air to fuel ratio around the stoich point (AFR = 14.7). Quote Link to comment Share on other sites More sharing options...
Ian C Posted December 14, 2009 Share Posted December 14, 2009 The sensor should be fluctuating between approximately 0.15 V and 0.85 V. Here's a graph shamelessly stolen from stealth316.com: http://www.stealth316.com/images/o2sensor-output.gif You can see that the voltage varies rapidly for a small change in air to fuel ratio around the stoich point (AFR = 14.7). From here: http://www.mkivsupra.net/vbb/showthread.php?t=35940 You should see, at warm idle, a hunt between 0.5v and 0.7v. Any solid figure between 0.8 and 1.0v is running too rich and the ECU can't compensate. Any solid figure under 0.4v means it's running too lean and the ECU can't compensate. That's from solid experience and proven to be correct on Supras Your narrowband reading being all over the shop may be because of misfires due to the mix being too rich. A misfire causes an artifical lean condition in a cylinder, which confuses the lambda sensor when mixed with the rest of the exhaust. -Ian Quote Link to comment Share on other sites More sharing options...
kill1308 Posted December 15, 2009 Author Share Posted December 15, 2009 Cheers for the info guys.... looks like I'll be changing the O2 sensor then Quote Link to comment Share on other sites More sharing options...
pistonbroke Posted December 15, 2009 Share Posted December 15, 2009 If you wanted to go one further with verifying the fault, I've heard you can remove the sensor and stick it in a lemon overnight to clean it. Then stick it back in to see if it makes a difference. Quote Link to comment Share on other sites More sharing options...
mellonman Posted May 18, 2010 Share Posted May 18, 2010 Hi i have this proplem too tryed the lemon juice thing but only put the reading down to 0.74 for about a day and now i am back to 0.83 so should i replace my o2 sensor? would like to know how you got on with replacing it did it help or have you not bothered? Quote Link to comment Share on other sites More sharing options...
Nic Posted May 18, 2010 Share Posted May 18, 2010 (edited) If the oxygen sensor is duff the ECU defaults to a rich mixture which makes the car very thirsty. They are not cheap but a new one will pay for itself in fuel savings in no time. The engine should also feel smoother and livelier at low rpms. They are not difficult to replace, just a couple nuts to undo and plug to disconnect. They are a bit fiddly to get at, removing the turbo heat shield will give you access from inside the engine bay. Reset the ECU if you do fit a new one. Edited May 18, 2010 by Nic (see edit history) Quote Link to comment Share on other sites More sharing options...
Konrad Posted May 19, 2010 Share Posted May 19, 2010 Cheers for the info guys.... looks like I'll be changing the O2 sensor then Erm... your O2 sensor is fluctating between proper values. Check coolant temperature sensor. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted May 19, 2010 Share Posted May 19, 2010 A normal O2 sensor is little more than a switch, the reading will go either side of 0.45v which is the threshold, more than this and the engine is running lean, less and its running rich. The ECU will just monitor the voltage and compensate, it has no idea what the AFR is, it just responds to the voltage, and most ECUs respond in the same fashion. Some reading here:http://mr2.com/TEXT/O2_Sensor.html Quote Link to comment Share on other sites More sharing options...
mellonman Posted May 19, 2010 Share Posted May 19, 2010 so does the oxygen sensor control the car running rich or just moniter it? nic what is your price on a stock o2 sensor and how much for a wide band o2 sensor Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted May 19, 2010 Share Posted May 19, 2010 so does the oxygen sensor control the car running rich or just moniter it? nic what is your price on a stock o2 sensor and how much for a wide band o2 sensor Both! It basically monitors the lambda voltage/ AFR ,and tries to keep it around stoic = 14.7 AFR which AFAIR equates 0.45V maybe very slightly less, The ECU sees the voltages change either side of 0.45V and increases or decreases the injector DC/duration to keep the AFRs to around the ideal 14.7AFR Quote Link to comment Share on other sites More sharing options...
mellonman Posted May 20, 2010 Share Posted May 20, 2010 so a wide band o2 sensor is better for correct fueling are they a stright fit or have to wire in as should have more wires Quote Link to comment Share on other sites More sharing options...
Nic Posted May 20, 2010 Share Posted May 20, 2010 so a wide band o2 sensor is better for correct fueling are they a stright fit or have to wire in as should have more wires If using with an aftermarket ECU. With a stock ECU use a stock O2 sensor. Sorry I'm not trading at the moment, due to ill health. Quote Link to comment Share on other sites More sharing options...
mellonman Posted May 20, 2010 Share Posted May 20, 2010 sorry to hear that nic but thanks for the information and hope you feel alot better soon:innocent: Quote Link to comment Share on other sites More sharing options...
mellonman Posted May 25, 2010 Share Posted May 25, 2010 just to let everyone know have now fitted new sensor and have the correct voltages now goes between 0.5 and 0.7 nothing higher nothing lower so we will see but just went for a blast and seemed to pick up better off boost might be just me though[GRIN][/GRIN] Quote Link to comment Share on other sites More sharing options...
little num Posted May 25, 2010 Share Posted May 25, 2010 Strange reading this, i have a cruising and idle problem, i have a vems afr gauge and it mostly reads 20 - 22 on idle and the engine is just about holding on (almost stalls) and then cruising its around 19 but then WOT shoots down to 11.0 - 11.5 so not bad on boost, whats the best way to clean the 02 sensor. And its greeeaat on fuel lol. Quote Link to comment Share on other sites More sharing options...
Brazil Posted May 25, 2010 Share Posted May 25, 2010 Strange reading this, i have a cruising and idle problem, i have a vems afr gauge and it mostly reads 20 - 22 on idle and the engine is just about holding on (almost stalls) and then cruising its around 19 but then WOT shoots down to 11.0 - 11.5 so not bad on boost, whats the best way to clean the 02 sensor. And its greeeaat on fuel lol. Couldn't this be a problem with a dirty ICV..? http://www.mkivsupra.net/vbb/showthread.php?t=210956&highlight=icv Quote Link to comment Share on other sites More sharing options...
mellonman Posted May 26, 2010 Share Posted May 26, 2010 well i did try the lemmon juice but didnt work well i guess you could try cilit bang but have not got a clue to be honest you cant clean them affectively the heat from the exhaust keeps them clean its just the sensor braking down making resistance tollarances greater Quote Link to comment Share on other sites More sharing options...
CanisLupus Posted June 20, 2010 Share Posted June 20, 2010 Didn't want to open a new thread so i'm asking here. I've checked the Lambda readings(Ox1 port and ground on battery) today with warm engine idling and got readings between 1 and 2 Volts sometimes even over 2 Volts oO I presume right that the O2 Sensor is down or do the J Spec TTs have other voltages? Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted June 21, 2010 Share Posted June 21, 2010 A average std type narrow band lambda sensor will have a signal voltage output of 0-1 volt with the switch point for the ECU being 0.45v which will approximately equate to 14.7 AFR. There are other types of sensor that output a changing resistance in response to the O2 levels, usually a sensor with an output of 2V or more usually 5V is a wideband sensor. So if your seeing voltages of 2V or more, then you are either measuring it wrong or the sensor is completely fooked. Quote Link to comment Share on other sites More sharing options...
CanisLupus Posted June 21, 2010 Share Posted June 21, 2010 So if your seeing voltages of 2V or more, then you are either measuring it wrong or the sensor is completely fooked. Measured like it's said in the FAQ here. Positive on Ox1 Port of the Diagnostic box and negative on battery ground, tried some other grounds everywhere the same. Right way to do it? The meter I'm using is a professional one which cost many $$$ so i don't think it reads wrong Readings were about 1,8V dropping to 1,05 and up again to 1,8/1,9. Suddenly over 2 and staying there. When revving it changed a little but not much. If everything is ok with the measuring i guess the sensor is crap? Quote Link to comment Share on other sites More sharing options...
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