I was wondering if the O2 sensor voltage should be reading rich at wide open throttle while the engine is under load. My RB30DE has some issues under load where it pings as some of you may know,I tapped into the 02 sensor wiring and went for a drive,when the engine is under no load and you back down the gears and open the throttle,the motor runs rich (about 0.7 - 0.8 volts),the mixture when I open the throttle right up under load (labouring the motor ) drops right down to 0.11 volts (very lean),I stopped the car & checked the fuel pressure on the in line gauge and revved it up,the fuel pressure went up with the revs (which it didn't do the other day). I gave it a hard rev for a period but not at WOT,the voltage on the multimeter displayed 1 volt ( constantly rich) and stood there whilst idling,jabbed the throttle and it changed down to about 0.25 volts. I understand that the O2 sensor should be reading 0.75 whilst idling,is that correct? The motors performance actually picked up after doing that. Is this the sign if a faulty O2 sensor? I think it could also be a fuel pressure problem.

I would say invest in a cheap JayCar Air Fuel Ratio, save messing about with a multimeter, plus a multimeter can't sample fast enough for accurate readings. I have a Air Fuel Ratio guage in my car and its extremely useful. (Even though it is a narrow band sensor) Basically, at cruise speeds, (light throttle, high vacuum) the ECU should be in closed loop, the Air Fuel Ratio will be cross counting continually from Rich to Lean and vice versa(0.1V-1.0V constantly). The multimeter probally won't be fast enough to show this though. If you stab the throttle, the mixture should go rich instantly (acceleration enrichment) with a stock ECU the O2 will show close to 1.0V (Stock Nissan ECU's run notoriously rich). Under load (Very Low Vacuum/or boost) the mixture should be rich (once again a stock ECU will show 1.0V on the O2 sensor) Under heavy de-acceleration, the mixture should go lean or cut off altogether. (0.2V or less) Under idling conditions the ECU should be in closed loop as well(crosscounting continually between 0.1V-1.0V), but I wouldn't worry about this to much, as its quiet difficult to calibrate the AFM to get the ECU to get into closed loop operation. The 02 sensor only comes into play under closed loop operation, the ecu uses the sensor to maintain a stoich ratio (14.7:1). Not only does this help fuel economy but this is where the Cat Converter works best/most efficiently. The 02 sensor has no bearing under open loop condition at all, for open loop, the ECU relies entirely on the AFM and other engine sensors. If you had the car under heavy load and the mixture was lean, no wonder it was pinging its ass off. Once again don't rely on the Multimeter to much. Ideally what you need is a Fuel Pressure Guage and Air Fuel Ratio meter in the cabin, whilst you sort these issues out. The main reason I have gauges in my car is i find them extremely useful to diagnose any potential faults, they are very useful.

I had been contemplating on getting one of those Jaycar mixture meters,right after I get my car alarm & engine immobiliser,I fitted a new O2 sensor I had bought when I had other problems (ECU was shot with the package I bought) but hadn't fit the new one yet. I fitted the new unit and had the multimeter connected to the sensor output,took the car for a drive and under even a light stab of the accelerator the voltage jumped up to 0.75 - 0.9 volts (within that range everytime I did it),but when I laboured the motor the multimeter went to zero volts,could that be an out of range signal? When the revs started to pick up the voltage dropped sharply to around 0.7 volts. The thing is before the the car went sluggish,I noticed it this morning when going to work,I had to pull into an intersection and there was a slight hesitation under load (no one else in the car would've noticed but),my brother borrowed the car and was saying how sluggish it was in the morning then for some reason it was o.k. in the afternoon,when he came to pick me up it went sluggish. That is when I took it out and gave it a hard rev and the motor performed better after that,the voltage from the O2 sensor went to 1 volt but wouldn't come down after the throttle was closed,it was then I decided to fit the new unit because I believed the old one wasn't sampling anywhere near fast enough. I'll just see how it goes as I may have mentioned there may also be other underlying problems in the fuel system causing this.