Strong gas smell when starting

Z_ealot

Interesting, so if i understand that thread correctly nissan mainly uses the af sensors to determine fuel trims. It does leave me wondering as i have only changed out my bank 1 af sensor if maybe the bank 2 sensor is throwing everything out of whack as that sensor is way overdue to be changed out?


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Jhill

All cars use the AF sensors for fuel trim. The mafs + rpm determine what cell on the map the car is in and the AF sensors give the feedback to verify the AF is matching the desired AF. What I was talking about was Nissan in the oem data does not list or use stft or ltft it uses that alpha data, something a bit foreign to me but I guess it’s like a combo of both.

Can’t say for Nissan but in my experience AF sensors don’t “age” and get lazy like a classic o2 sensor. If it’s way off you can use the rear o2 vs front AF readings to see if something is up.

Z_ealot

Any best method for testing with the rear o2’s?


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Jhill

I have not used this method to test post cat but I’ve heard it still works even post cat (maybe a slower switch), you can make a vacuum leak and watch all sensors react to it, rears should go low voltage like .1 ish and the fronts for the z I believe (I would need to double check) are a 0-5v with 5 being lean I think. If I remember reading right the nissans are opposite what a conventional o2 is and given in voltage. I found information on them before and they are a little different than some of the other AF sensors but now I cant find it.

Then you can force it rich with a little propane and watch all sensors switch.

Not sure if snap throttle method will work for post cat testing. Just an FYI some manufacturers actually use the post cat for fuel trim as well, some are more open about it than others like Toyota I believe the rear o2 heavily effects fuel trim.

Z_ealot

I read in the fsm concerning the fuel system that the post cat o2 are not used for fuel trims when in closed loop mode, but then it goes on to say they are used in open loop and also to fine tune the fuel trims in closed loop mode....confusing to say the least


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Jhill

Ok so snap throttle does work.

Slam throttle hard accel onto freeway (didn’t get that cap) and than snap off throttle. Also a cruise shot where they stay fairly middle of range. Should react fairly quick.

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Z_ealot

didn't get a recording of the wide range voltage which I believe my scanner is capable of picking up, but I did get a snapshot of what the post cat O2's are doing, to me at least if i'm interpreting it right it looks like my post cat O2's are reading a rich fuel mixture at cruising speeds compared to yours