Narrowband oxy sensor Page 1 / 2

morrisman1, Jan 17, 4:10am
Thought Id bump this to the top, I ended up fixing the issue. After finding my fuel pressure gauge I put it on and found it was dropping pressure down to 24psi as the demand increased. swapped fuel pressure reg in case it was leaky. Had injectors ultrasonic cleaned and flowed as one had a buggered o-ring and was leaking heaps, and finally found the fault as being the high pressure flexi in the tank from the pump to the tank fitting, it had perished and cracked so was leaking.

After replacing that I now have proper fuel pressure 37 psi idle, up to 50psi on boost.

Interesting fault finding exercise in all and took far too long but all fixed now and its running like a dream.

msigg, Jan 17, 4:43am

morrisman1, Jan 17, 7:33am
what do you mean?

intrade, Jan 17, 8:05am
"It reads the normal fluctuations at cruise and idle, but at WOT reads lean"
End of cp that was your clue at wot lean means its got not enough fuel. pressure test of fuel is the frst step then injector balance test.
he probably refers to you swaping parts you can check a pressure regulator without removing it unless you dont have the tool or knowhow of course .
checking pressure on rail if its got a shrader valve is most easy . next test should be befor the fuel filter this way you can test if the filter is blocked up if you get almost the same readings befor the filter then the problem is further back.

morrisman1, Jan 17, 8:25am
I did test the fuel pressure, and with it not maintain what it was meant to, and leaking down to zero after shutdown then I suspected a regulator issue. If you have the parts there, then why not do a swapatron to eliminate a component?

I see what you mean intrade with it reading lean - the narrowband wasn't lying it seems. But what became confusing was when a wideband read normal AFR (but car was running fine for once during that test so I couldn't confirm if the narrowband was right or not).

msigg, Jan 17, 8:51am
morrisman1 no offense, it's Intrade's favorite word, I thought I would mention it. You did well, yes if the parts are there why not.

snoopy221, Jan 17, 9:02am
WTF am i doing skipping posts and simply posting?


W O T is sensed by T P S and gives a 9 percent increase in injection volume.

Go bak ta damn basiks T P S. WOT.

morrisman1, Jan 17, 9:48am
Go easy on the moonshine snoop dog.

snoopy221, Jan 17, 10:24am
Aye by Gum laddie.
Most TPS from factory ar like 50 thou or so on the idl and they can be stepped (Tweaked) in to 10 thou bringn the ole 10 per cent increase in earlier.
But tya yng bkwds cap beeeenie wrn lowered seat railers.
Yae cannae realise input=output.
Or if ya dannae Ken-yasss blmn da moonshine. LOL

aredwood, Jan 17, 11:42am
Nissan most likely set the fuel maps so it will always run rich when ECU is running "open loop" And then use oxy sensor readings to lean it to stoich. With factory oxy sensor working = correct AFR values at cruise - Low fuel pressure under boost causes leanout. Factory oxy sensor disconnected = too rich under cruise, leanout still happens under boost, But due to AFR being too rich to start with. It only goes from very rich to a little rich.

If you had been able to leave the factory o2 sensor in place as well as your wideband sensor. You would have picked up the leanout straight away.

morrisman1, Dec 5, 9:47am
Im just trying to work out why my GTIR is going into limp mode after about ten minutes running. I put it on the wideband sensor today and it was reading all good, but we noticed it stopped going into limp, and no matter how hard I pushed it, up to but not over 101km/h, I couldn't get it to replicate the results and go into limp. So that makes me think its the narrowband sensor (which is about 10,000km old)

It reads the normal fluctuations at cruise and idle, but at WOT reads lean. Im not sure what they are meant to do but I thought it would just read rich as the car is actually running at about 11:1 AFR on the wideband under the same conditions.

My thoughts are that with it indicating lean the ECU is going into limp to save the engine from what would (if true) would cause detonation.

Has anyone got any feedback on the normal readings of a working narrowband during rich mixtures?

aredwood, Dec 5, 10:57am
Are both sensors installed in the same place in the exhaust? Supposedly if an oxy sensor overheats it will read lean in error.

mechnificent, Dec 5, 6:58pm
Most cars ignore the O2 at full throttle and resort to a fixed rom. The symptoms do sound like O2 though.
As far as readings go, it should read between about point one and point nine.

mechnificent, Dec 5, 7:00pm
It doesn't have two sensors does it ? And the cat is malfunctioning.

bigfatmat1, Dec 5, 7:09pm
as above o2 ignored at wot. should run rich Pretty sure only has one sensor on these. Unless you have a aftermarket or modded ecu

mechnificent, Dec 5, 7:28pm
Yeah. that's what I was thinking/wondering about the lean at full throttle. someone has reprogramed the ecu.

These cars that have been modded are a nightmare if the owner doesn't know what has been done. I generally keep right away from them.

mechnificent, Dec 5, 7:32pm
Oh. and a rich reading will be near the point nine. lean is near point one.

pericles1, Dec 5, 8:55pm
Have you tried taking negative off battery and resetting ECU?

intrade, Dec 5, 9:03pm
Ok to make one thing clear a narrow band oxigen sensor is completly different from a" wideband air-fuel ratio sensor", that is the therm for the wideband sensor, it also functioning complete different with a signal going in opposite direction, as what narrow band or lambda 02 sensor do. I hope you know that if not you do now.
Next thing would be where do you get your readings from as above are correct the computer ignores the signals, dont means you wont see the signals displayed the most accurate signal you will get from backprobing sensor and a scope , as anything else is not live data its processed data and can be wrong processed obviously.
fueltrim data is what to understand and the 2 sensors working opsite dont makes the whole thing any more easy to learn.
so if you really want to learn how the sensors work and how the data is used in a ecu you would want to take the "scantool class from aecs" he covers fueltrim on the scantools .

morrisman1, Dec 6, 6:38am
Ive tried resetting the ECU from the diagnostics. They only have one o2 sensor, its a titania style one which the ECU measures the resistance of.

ECU, engine, everything is stock. wideband sensor has confirmed that AFR is normal. It should tell me that its rich at WOT, but its saying lean (wideband is reading about 11:1 AFR - so rich).

I know how the ECU uses the data, but Im not sure if it receiving an incorrect lean indication under acceleration is causing it to go into limp.

intrade, Dec 6, 7:54am
ok you want to take some professional training as the ecu does not mesure any form of resistence on any oxygen sensor nor on a wideband sensor
it goes in to limp mode because the ecu cant compensate for the condition. like low fuelpressure is a lean condition under heavy load thats just one example of why it could go in limp mode mass airflow reporting incorrect data or vaccume leeks "at idle* also cause lean conditions
Fueltrim data of long and short trim would need to be inspected to see what direction to take
but you whiped out that data probably by resetting th ecu. You should seriously do the course for 600+$ from post 9 you wont be erasing codes nilly willy after the course as it contains vital clues for more easy diagnostic.

intrade, Dec 6, 7:57am
Back to the problem you fitted the car that has programming for a normal oxy sensor on to a wideband? or was there always a wideband sensor on there- ?

morrisman1, Dec 6, 9:18am
So are you saying that Nissan are wrong in their factory service manual intrade?

Also why would an independent wide-band sensor read completely normal AFR, 13.5 under cruise (no trimming cos the factory 02 was disconnected at this stage, it normally trims down about 10%), 11:1 under WOT. This is showing me that the car is not actually running lean. How hard is that for you to understand, I've already said that.

I put a wideband in it which was completely independent of the ECU for diagnosis reasons, to see if it was actually lean at WOT or if the factory o2 was telling porkies. It is a 1990 ECU, it doesn't have that much self diagnosis other than knowing when components go open-circuit. It does have the ability to drop to low-octane maps if detonation is detected, and I believe this is a separate function to limp mode. In low octane maps it retards the timing across the board about 5 degrees

bigfatmat1, Dec 6, 9:55am
disagree here. Morrisman is correct in what he says titania sensor switches restance quickly via resistor pulling a 1 volt signal down to ground. Unlike zirconia sensor that creates a voltage titania works Like how a coolent sensor works. If car is running rich and 02 sensor is low voltage would possibly indicate a manifold or exhaust leak before o2 obviously

intrade, Dec 6, 9:29pm
manufacurer write a 600 page document on how a potentiometer works . they write stuff so complicated that you end up doing the wrong thing
they dont say the ecu mesures resistence they just confuse you to think that . thats a example of what manufacturer do not that anyone comes now and says there is no potentioemter on a oxygen sensor
its simply a example to show what manufacturers do.

Voltage drop occures when there is resistence yes correct its friggen ohms law.
the ecu gets feed the voltage not the resistence resitence is not mesured but the resultiing voltage fluctuation. of this aproximate 1 volt
A oxigen sensor is a voltage generator classic one wire toyota oxygen sensor on 90s toyota. generates 1 volt maximum if heated. and generates nothing if its dead.
Wideband sensors get a woltage in to them and it makes the voltage drop with its oxigene cell more accurate then the one who needs heating up first befor it makes anything , its why its called a wideband-air fuel ratio sensor= a-f-r its signal is oposite of what the o2 cell do so you can not swap out a old oxy sensor for a air fuel sensor both send voltage to the ecu but the meaning is different for high and low voltage.

So i am still stuck not knowing if you changed from a old o2 sensor to a wideband as you cant do that i explained it now 3 times why not.

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