AFR problems
 

Hi there,

2015 Nismo 6MT BP single kit, Motordyne exhaust, open dumps, stock block, ID 1050cc injectors, 340lph pump, s1.e fuel return, remote tuned by Seb @ 12psi. 33,000 miles, about 8000 on the turbo kit. For the first few months, car ran perfectly. Then, overnight, my aftermarket AFR gauge starting reading about 1 unit richer at idle. The weird thing is, the oem sensors still read 14.7. I thought no problem, the oem sensors went bad. I replaced those and the problem remains. Then I thought it was the aftermarket gauge. I replaced all the wires, sensor, gauge, module, and the problem remained. You can definitely smell the extra gas. At WOT, the afr is also richer but is within acceptable values. (10.5-11.5). Another symptom, when cruising, and letting off the gas, about half the time when coming back into the gas, the cruising afr is super rich at about 12:1 for 20-30 seconds before normalizing back to 13.5-13.7.

The car is still lightning fast and if it werent for the afr reading itself, and the smell, you would never know anything is wrong. But I figure it’s time to get to the bottom of this before things get too fouled. If anyone has any ideas before I throw more parts at it I would appreciate it. Thanks

Here's a video Seb posted on Youtube last night showing how you would be getting different readings from your factory sensors than your aftermarket gauge sensor(s). I know it doesn't answer your issue but still good info. Have you emailed Seb, he'll probably want to look at your logs.

https://youtu.be/zf3U7OxlwHY

Neat video. I have spoken to Seb about this problem in the past. I sent him logs and he even adjusted the tune for the WOT richness. Honestly, I think he kind of grew tired of me complaining about the unusual behavior I was experiencing and he attributed it to normal divergences that he displayed in the video you posted. He said it was normal. The reason why I beg to disagree, for my case at least, is because it did not do this when he initially tuned it and for many months and thousands of miles after. Additionally, the AFR divergences are most notable at low loads (idle and cruising) rather than high loads, as you might expect. This is why I began to suspect a mechanical defect. But I can’t think of what defect would cause this. So, perhaps we should just try tuning this condition out? Of course, that should be the last thing we try, hence this thread..

I realize this was kind of a shot in the dark. It is difficult to diagnose problems like these over the internet. But it was worth seeing if someone had experienced something similar.

Thank you for your input!