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O2 sensor

itsallgood

By itsallgood,
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poyz Proficient

poyz

Posted
Posted

As far as I've had it explained to me the factory ecu works as follows from the engine speed input and the air flow meter input the ECU calculates a pulse width that should give a stochiometric air:fuel ratio ie 14.7:1. The with that speed and air flow information it looks up a table which contains a number. That number is a multiplier for the pulse width. I do not know for certain, but I don't think that the multiplier can be less than one, ie acts to shorted the pulse width with should give an leaner mixture then 14.7:1.

If you are running in closed loop mode, the ECU can run leaner, but anything over about 30% load/throttle and the ECU will not enter closed loop mode, ie the 02 sensor isn't even looked at most of the time.

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predator Grand Master

predator

Posted
Posted

Adding to the above, the oxygen sensor (I'm assuming you are talking about the one off the exhaust?) is not the only one that the ECU makes it decision, and its a balance of that, AFM sensor, the intake air temp (before the intake manifold), and THR position (butterfly open/close %). Then of course it has to work out how much fuel is going in, boost levels, etc.

Its a complex equation thats for sure!

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blind_elk Grand Master

blind_elk

Posted
Posted

The only time you should have noticed the O2 sensor was faulty would be on 'cruise' (constatnt throttle, constant speed). On a WOT ie accelerating, which most dyno runs are, the O2 sensor would be out of the equation. Nissan programs the ECU to run rich-as on WOT.

So its possible the dyno operator was having a lend of you.

I have replaced mine - for a different reason - and it cost about $150 from Nissan (its a NGK unit, so you might try contacting NGK).

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darkhalf Community Regular

darkhalf

Posted
Posted

im in the middle of building an Air/Fuel meter from one of those jaycar kits. it says the chip in the kit is matched to a particular bosch o2 sensor (making it not perfectly accurate with other o2 sensors). this is because of the skew of the lamda values outside stichiometric ratio (14.7) can be different between various sensors.

anyway to use this accurately on my r31 im going to have to reprogram the PIC chip mappings

hence i think you need an o2 sensor which reports similar lamda values to the original one (for the factory ecu)

mine is rattling (ie stuffed - the sensor inside is broken in half) and i'm planning to go the NGK ones for my RB30 which was $130 repco

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