Lean at vac 3k to 5k
 

Hi, Is it ok to be super lean like 17+afr when vacuum is in the teens or lower and rpm is like 3000+?
Basically this is a no throttle situation and pretty sure only when coasting in gear. For cruise speeds I have afr of 15 and 15.5 for slightly higher vacuum.

Thanks
1.8 BPT
2.5 pipes
Microsquirt

Go to Tunerstudio (I believe under fuel settings but don’t have my laptop with me) and check if you have “fuel cut overrun” enabled. If enabled, this feature cuts fuel when you’re cruising off-throttle and allows the engine to be rotated by the vehicle’s inertia, saving fuel. All modern cars that I’m aware of do this. That would explain your lean AFRs under those conditions.

Depending on your settings, it usually takes a couple seconds to enable if conditions are right. I was also confused by this when I first installed my MS/wideband haha.

I actually turned on overrun after i noticed the above and now it really goes off the chart with lean 22 or more, which is expected from over run and hopefully will get me closer to 20mpg. very weird i was having lean spikes before the over run setting but at this point it seems to be doing what it should be doing. Back when i had the BPT matched ECU i was getting about 22mpg so my physical setup can and should still get that but my tune is preventing it.