Sudden lean AFR's at Idle and cruse only !
 

Hi,

What will cause the above ? The car was fine and suddenly started to go lean 16~18 AFR on idle and 15~16 on cruse ! WOT perfect.

I have double checked the following;
No exhaust leaks
No vacuum leaks

The tune never been touched ! as the trims were perfect with the current settings ! So is it because of FPR or Plugs or Coils ?

I don't run on O2 sensor been disabled, HKS 1000cc, Kelford 272. Before this my AFR's were 13.5 Idle 14.5 cruse same as my map AFR's. But now as above problem !

Bad wideband o2 sensor, fuel pump on the way out, boostleak hope you have tbolt clamps all around hope. I would double check the tune too.

When the car goes lean during idle does it feel the same or does it shake/vibrate, drop revs?
My guess is that it's either a problem with your front O2 or your WB O2.

This sounds like the issues I am having as well, my friend.

This week I am preparing Megatron for his remote tune by Tom on Saturday morning. I am pretty excited about this. Currently, my AFRs are in the high 18-19+ range and that is encouraging even on pump/91. The off throttle bucking around town needs to be smoothed out as was as the idle which is currently set at 1,200 RPM.

My car encountered the same symptons recently until the CEL finally came on today and it was for a faulty map sensor ( I run a Omni 4 bar and made a thread about it). Have yet to replace the faulty sensor because after getting my alignment today, the CEL turned off lol

impact blue & HaVoC187

Thanks, but as I stated before that my front O2 is disabled from the tune ! so running on MAP fueling, also I did able it to check if its toasted, but I do get reading from it and its showing signal .7~.9. Also no issue with fuel pump as I am running double pumps, but really need to know how faulty WB O2 going to effect this ! also I have removed it to check but still the same

But one thing I have noticed during evoscan is the my timing advance is not stable ! it's dropping to -1, then 0 then between 4 to 7* as in the map its set to 18* ! I have replaced to new plugs but no change ! still showing the same ! could it be the coils ?

I thought you were talking about the rear o2, I didn't even know you could run without a front o2.
If the WB o2 is on it's way out, it could give faulty readings making afr on your gauge go lean while it really isn't.
If it is really lean you should feel it.

our models Evo 6.5 don't have rear O2, and yes you could run without front O2 ! meaning you disable it and run open loop all the time ! good If you have big cams and really want to avoid lumpy Idle's. My car Idles around 13.3~13.5 timing advance to 18* on Kelford 272 and no lumpy idles ! feels like stock cams, and regarding WB O2 really I don't think its faulty, because I calibrate it frequently and all looks fine and readings are +,- .1 or .2 the most from my base map, guess have to do a boost leak, and vacuum leak test all around as I think its mechanical related and not tuning issue.

Perfectly normal. Your car is going into closed lope for fuel savings etc.

your front O2 sensor is failing.