Quote:
Originally Posted by Techno Duck
The puzzling thing is your saying bad MPG, but your data log looks like its running lean during city driving and normal at steady cruise.
Your saying no soot on the tailpipe or bumper so the only other place for it to go is in your oil. How many miles are we talking since this has been going on? Oil may smell like fuel if its bad enough, or send it in to be tested. The low tech way is to compare viscosity with a new sample of the same oil. Put a small amount on a piece of glass and hold it at an angle, both samples should run the same amount over time. Look up lube oil viscosity race test to see what i mean.
With the data log you posted, the reason i question the air flow meter is the test you did only checks the carbon track for wear. If the carbon track is worn, you will experience bucking or hesitation when accelerating.
What you cannot test on the air flow meter is how far the barn door is opening at a set engine load. This is what influences your air fuel ratio at partial throttle conditions. Adjusting the clock spring changes the tension on the door. Less tension on spring means the door opens further than normal, so it will run richer. More tension on spring means the door opens less, so leaner mixture. The clock spring can really only be set using a flow bench and to my knowledge ive never seen official numbers on where to set it at posted. The clock spring in the AFM never needs to be adjusted, unless you know the full history of your AFM i would still question it.
More info on the AFM and the clock spring;
https://forums.pelicanparts.com/porsche-911-technical-forum/835870-afm-mixture-am-i-lean.html
https://forums.pelicanparts.com/porsche-911-technical-forum/1105174-air-fuel-meter-adjusting-screw.html |
Actually, the AFM can be tweaked using a CO tester, e.g. from Snap-ON, very easily with good results, nothing complicated here!
I've tweaked numerous 911 3.2 AFMs to pass emissions tests, and then re-adjusted for optimum performance.
Followup testing an be done using a wideband O2 sensor under various driving conditions.
Now when to get to a 993 and later Porsches with MAF sensors, tweaking AFRs are basically impossible.