I had to replace a disconnected rear O2 sensor (behind the cat) so I would pass emissions (I was throwing a code). Afterwards, you have to reset the ECU to get the SES light off. I left the battery disconnected overnight wednesday night, and drove it to work as usual. The acceleration and power is markedly decreased compared to before I reset it. Especially below 4000rpm, it is sluggish to say the least. It shifts a little below 6000 when floored, it used to shift at 6000. Before I reset it, I could lay down rubber off the line, now the most I can get is a tiny chirp, no spin. What is going on?

 

the o2 sensor you are talking about in your fed spec maxima is a secondary o2 sensor. it only monitors the cat and has no impact on air/fuel ratios which means it is not affecting acceleration. the two primary o2 sensors (one for each bank) and the mass air flow sensor determine your a/f just cruising along and the maf is solely responsible @ wide open throttle.
you cannot measure acceleration by the amout of tire spin. are you sure the secondary sensor was the problem and not a primary? what code did you have pulled?

 

Not true, the Nissan guy confirmed that the rear O2 sensor does in fact affect the fuel map. I am positive that was the problem, I cut all the wires 4 months ago, the sensor has been physically disconnected. While it was disconnected, it wasnt running perfect (still isnt, I need a tune), but it had significantly more power). It was P0141. Obviously wheelspin is not a valid indicator of power, but there is a huge difference in the off the line performance. I'm not an idiot. Any ideas?

 

i never said you were an idiot, im stating fact. why do you think an o2 simulator can mock a secondary o2 sensor and not a primary? because the secondary only monitors the prescence of a cat. thats why when you get put a test pipe on a fed spec maxima, it will trip a cel for catalyst below efficiency. how exactly did your nissan guy confirm this by the way? one of the reasons i know this is i had both secondary sensors unplugged from their connectors for over 3 months after my headers. there was no lack of power and the only gas mileage drop was attributed to me mashing the car to feel the new power. in fact, after i got over that, my gas mileage improved quite a bit even with both disconnected.

 

He just said it had an effect on the map, he may be wrong. Then why do I have so much less power?

 

is the ses light still on? is the negative terminal tight on the battery post?

 

I have a similar problem... The SES light is on and the Nissan dealership said they need to replace the o2 sensor in front of the cat and reprogram the ECU.. Total cost =$475 Is that typical cost? Is there anything else to correct the problem. By the way I do have the high flow cat from customenterprise.

 

SES light has been out since I hooked the battery up again. The terminal is tight, yes. Any ideas?

 

i know you said it felt sluggish below 4k but does it feel the same above? do you feel the power loss cruising around or @ wide open throttle?

 

yeah, the whole power band is suffering, but the biggest losses are below 4k

 

I also have 'chugging' right when I start her up cold (not cold weather, just cold engine). I was reading another thread, I have identical symptoms to another guy who had a bad MAF. loos of power, chugging, etc. Im almost positive its not my vias cause its better in the high revs than in the lower ones. Any reason I shouldn't buy a new MAF?

 

I had the same symptoms before I replaced my MAF sensor. I got it from Dave B and it was $80 something dollars. Money well spent, in my opinion; for the results. Your call. Also in regards to reseting the ECM. The computer has to re-learn your driving habits. So it might feel diffrent because of that. In your case though sounds like your MAF might be going out.