engine and drivetrain Air Fuel Ratio Sensor Installed: Autocross Photos

gliding_serpent2 · May 2, 2014

Had a number of things done to my tii including the 3.91lsd, and a air fuel sensor. When warm i get 13 at wot, 13-14 part throttle. Idle when warm is lean at 14-17 however.

Edited May 4, 2014 by gliding_serpent

gliding_serpent2 · May 3, 2014

More details. The sensor was welded vertically a few inches past where the exhaust manifold joins to a single pipe.

Idle is 14-17 and about 800-900rpm. It does not stall, but sounds a little sick at times.

Partial throttle is 12 to just over 14.5 warm in 4th. 12 is breathing on the throttle. 3.5k rpm (3.91 ratio diff, 4 speed) in 4th says 65mph. This is light throttle. Just under 14 at this throttle. More throttle leans it out up to 14.5 in a pretty linear fashion (hills for the same speed add about 0.5) with max on hills a hair over 15.

WOT is 12.5 to 13.5 (latter hill in 4th).

Lift and it goes to 18, but no backfiring.

Jgerry2002 once posted "At WOT you should be (ideally) ~12.5-13, idle Tii's seems to like about 12.9.-13.1. Cruise should be ~15. "

1. Is the sensor too close to the manifold and will this skew what i see? Looked similar to jgerock for position.

http://www.bmw2002faq.com/topic/97869-tii-running-issues-updated-2272012/?hl=air%20fuel

2. I feel i may be running lean at least for idle. How to i best adjust idle only? Simply the tuna can idle screw?

Edited May 3, 2014 by gliding_serpent

jgerock · May 3, 2014

Adjust the tiny screw inside the tuna can for CO at idle. You may have to adjust the outer screw for engine rpm as a result.

gliding_serpent2 · May 4, 2014

I turned the idle mix screw counterclockwise about 1/4 a turn for an idle that was 12-13.5 on the air fuel ratio. Much better, can idle all day long. WOT and part throttle was still as above.

That being said, I did drop in some STP octane booster (jet fuel) into the tank prior to my autocross event today. Seems like WOT moved from 13 to 13.5 afr. Part throttle was about the same, maybe 0.5 less lean across the board. I assume that is the booster, not the idle change. Hard to know given that I added booster, and changed idle richness at the same time.

anyway... photos. Not sure why the camera made everything so grey...

gliding_serpent2 · May 4, 2014

gliding_serpent2 · May 4, 2014

Not to brag, but I just wanted to state that my 40 year old car was about as fast as this modern tuned Subaru WRX STI... and that was with me babying my transmission and taking gentle starts. The driver was new like me and pretty pumped that he had beat a number of the experienced guys including our instructor. He was riding our instructor pretty hard. Anyway, I come over (I had the same instructor), and said "Congrats man, what was your time?" He said his time and that he only got one cone. I replied "Well you beat me too, as I was 3 tenths slower. But then I didn't hit a cone..." He shut right up. :-D My old girl is keeping up its rep as a bit of a giant killer.