AFR idle lower than 14.7
 

Hey guys,

So just Question - I’ve got FI test pipes and a Greddy exhaust on my 2016 Nismo 370z and I seem to be idling lower on my AFR than I should be? Or maybe it doesn’t matter.

Im idling at 13.8 - 14.1, which is what I’m cautious about. No other issues.

I talked to Seb and sent him some logs - he didn’t think anything of it - but said you can always check for an exhaust leak.

My AFR WOT is still normal - above 12.5 to 13.5 (May dip a BIT lower but so hard to tell when driving it)

Thanks.

Overall, it really isn't anything to worry about.

I suspect the cause is your test pipes.

Starting in about 2011, a "Rear Fuel Trim Monitor" was implemented in the ECM software.

As the front Air/Fuel sensor ages and gets exposed to contaminants, it can develop a rich or lean bias.

The rear fuel trim monitor system is designed to compensate for any of these bias shifts using the post cat O2 sensor. This system looks for any bias shifts at the stoichiometric point of the front air/fuel sensor and compares it to the rear o2 sensor.

Since you don't have a catalytic converter and the rear o2 sensor is generally out of the main exhaust steam to prevent P0420/P0430 (catalytic system below threshold) this might provide the ECM with information that it interprets as the air/fuel sensor has a lean bias, so it adds a little fuel.

If it bothers you, I'm sure your tuner could adjust the AFR targets for idle.

Question:
What are your long & short term fuel trims for both banks at a hot idle?

I'll check that once I get them hot enough. I tend to only drive a few miles a day back and forth from my job, and gym and stuff - and as of now with the virus - I'm not driving much at all, but I'll run it for 15 mins or so and get it hot.

Thanks for the information. I've also thought about retraining the idle - and resetting the ECU - but like i said, nothing is going on - nothing abnormal, but I wanted to make sure - so I don't cause any damage that could be avoided by catching it early.

Ok I pulled up my CSV file I sent Seb. Here's what it looks like (92 - 105 throughout the banks) - and those banks fluctuate from 92 - 105 throughout the drive.

Also - I do have my O2 sensors shut off from reporting on the codes... it kept turning my engine light on - not sure if that matters?

Unfortunately changing the fuel targets away from 14.7 will probably cause the ecu to switch to open loop fueling where trims are ignored. Your tuner should be able to disable (uncheck) the rear o2 sensors, this should help.

That's good to know :)

Ok so I should just ask seb to uncheck my rear 02 and it should get me closer to 14.7?

Those fuel trims look good.

There is no harm in doing a idle air volume learning and it would be interesting to see if that changes anything.

I don't know if turning off the O2 sensor codes just stops the code from popping up, or it is tells the ECM to ignore the sensor's output.

Anyways, I think you don't have anything to worry about - just enjoy your car :)

Appreciate the knowledge and advice!

If Seb didn't see any problems with it, then you are good to go :driving:

UPDATE: So I had 2 screws that were loose on the back piece of the exhaust - everything seems to be solid again!

Thanks for all the responses!