Hi,

I recently installed wideband sensor on my car(installed near the rear O2 sensor), and noticed lean AFR during idle, around 17-17.5. Front O2 sensor fluctuates between 0.5-0.7V when WDB is reading 17-17.5. I get more or less better AFR reading when cruising around 15-15.5. Any ideas why it is so lean at idle?

My setup:
Gsc S1 Cams,
Blitz Air filter.

Checked for boost leaks. No issues there.
Also didn't see any exhaust leaks, when visually inspected.

P.S. Don't know if it's realted or issue at all, but noticed that when pressing brakes during idle, AFR goes around 19-20.

 

Anyone? help please.

 

maybe its a tuning issue, show it to a tuner, he can mess with timing and fuel and make it better.

 

when you installed your cams and air filter did you get your car tuned? if not then it explains the lean AFR's because you need to get it tuned after installing cams.

 

Maybe a voltage issue. Just throwing that out there since pressing on the brakes shouldn't change a thing. Maybe the Alt is going out.

 

it might be, recently my serpentine belt was slipping causing lean conditions and bucking.

 

Thanks for replies guys!
I got tuned after I changed those things, I though it was exhaust leak issue since my manifold had little crack but I changed manifold, and it still remained. Tuner says this lean conditiin is caused by cams, meaning big overlap, and says he can't get it more rich.

What was the system voltage when you had that issue? I don't rally have any other issue(well turbo needs rebuild), idle is stable and runs/pulls more or less fine.

What causes confusion for me is that, O2 thinks afr is fine, as I understand 0.5-0.7volts doesn't mean it's lean. Also what that braking making it more lean, is it normal behaivor?

 

i didnt log the voltage, my serpentine belt was slipping and getting chewed up by the water pump, this was causing altenator not to work properly as the belt was slipping, i put on a tighter belt and the lean condition was gone.

if you can try replacing the altenator aswell.

 

You've probably fitted the sensor in the wrong place.

 

I installed it at the end of the downpipe, at 45 degree angle. Around 5-10inches before the rear O2 senror. Is that the wrong place?

 

That's fine.

 

Make sure the wideband has clean power and a clean ground. If it does not, it will show symptoms like you are seeing.

 

that is BS... I have gsc S2s and have perfect 14.7 idle even when I turn off the O2 sensor closed loop...

I would check the fueling with the OE O2 sensor closed loop correction turned off.. thast way you have good base fueling and can then see if the O2 sensor is giving you trouble..

which WB are you using?

 

If your afr goes leaner with the brake pedal depressed it can be a vaccum leak at the brake booster.

Go under dash and press brake pedal listen for a hiss noise from booster. Maybe spray brake cleaner at the back of the booster inside the car while pressing the pedal. See if engine stumbles

 

yeah, maybe he could block the vacuum line just to se if it behaves normally