AFR Maxed out but still lean

[PandA]

Morning everyone!
The car: 86 911, 270k miles, only upgrade is fabspeed exhaust.

I decided to stop trying to re-invent the wheel and stop trying to be super cheap. I purchased:
https://www.amazon.com/gp/product/B00N3VGPYS/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
"installed" using alligator clips, hooked up WBO2 and fired up the car. Holy cow was I lean!
Ended up tightening the screw on the MAF all the way (which unless something is REALLY wrong, should be making the car run more richly.) Even with the screw tightened I am still getting 16-17 afr.

I am 99% sure I do not have an air leak, but from those numbers, maybe I need to keep looking?
Other suggestions?

Andrew

[juanbenae]

did you unplug/disconnect the OE oxygen sensor to install the sensor for the AF meter?

[911obgyn]

I did the same thing a couple weeks ago, you have to bypass the idle control and adjust base idle speed while adjusting CO, sounds like you may need to find leak. I used the same wbo2 sensor make sure you calibrate in free air before you install it. Check plugs and make sure your injectors are clean or you will be adjusting around other issues.

[al lkosmal]

+1...a good question. That gauge is meant to be used with a wideband O2 sensor.....I believe the stock Carrera sensor is a narrowband sensor. If I remember correctly the narrowband voltage range is...0-1V and the wideband is 0-5V.....so mixing a narrowband sensor with a wideband gauge would result in incorrect readings.........some gauges allow you to select between the two.
Not clear if that is your issue, but........
regards,
al

[pampadori]

Well, you did claim to get 27mpg on a trip where you were doing 100mph the whole way. SO who knows....

BTW, you will not have a happy running motor at 16.5-17:1. It will jerk and pop and probably not be very driveable at all.

Originally Posted by PandA

My 3.2 with wife and stuffed to the gills did the San Antonio to Big Bend trip at 100+mph the whole way and we averaged about 25 to 27 mpg.

[juanbenae]

Originally Posted by al lkosmal

+1...a good question. That gauge is meant to be used with a wideband O2 sensor.....I believe the stock Carrera sensor is a narrowband sensor. If I remember correctly the narrowband voltage range is...0-1V and the wideband is 0-5V.....so mixing a narrowband sensor with a wideband gauge would result in incorrect readings.........some gauges allow you to select between the two.
Not clear if that is your issue, but........
regards,
al

in addition to what al suggests if you do not have the OE sensor installed that could play havoc with AF mixtures. ive never had an 02 sensor equipped 911, but would have to assume that with it disconnected you would lose the ability for the injection system to adjust mixture in real time. as I understand it the 02 sensor monitors exhaust and adjusts mixture for the best results in a given situation, like ambient temps, motor temps (such as during cold start warm up), and altitude.

[pampadori]

This is an interesting experiment. What happens to AFR readings when there is a leaking exhaust gasket or even a 1/4" hole within the headers? https://www.hotrod.com/articles/exhaust-leak-affects-widebando2-sensor-readings/

I was surprised how lean the readings went from just a small gasket failure. I guess I need to check for leaks more often on my car.

[911obgyn]

When you disconnect the O2 sensor it goes into bypass mode and with the idle air control centered and engine warm is when you adjust the air meter at idle. Then remove wbO2 install regular o2 sensor hook it all up remove jumper and engine management takes over.

[PandA]

Yes, WBO2 sensor was only plugged into the gauge.
The AEM claims that if you are using the correct Bosch SBO2 no calibration is required.

As far as 27mpg, it was running leaner than that before richening it up. Truthfully I am surprised I didn't melt valves or put a hole in a piston, and yes it would pop and generally up upset with life under partial throttle coming down a hill. Under load it would richen itself up enough to run well. As for city driving there is alot of wide open driving to get into the open loop maps on the computer so it would not act like an idiot.

Having just put on the new exhaust I am satisfied that it is sealed correctly.
That being said I probably should put a wrench on it again to make sure the SS hasn't loosened up on the gaskets.

Other than check exhaust gaskets any other suggestions?

['76 911S 3.0]

How long ago did you purchase the gauge?

[911obgyn]

Check for vacuum leaks also, did you use the wbo2 sensor that came with the gauge to read co levels?

[PandA]

I purchased the gauge two days ago, yes, using the same sensor that came with it.