Very low mpg, help plz

[911monty]

Hey JayG; Good to have an instructor chime in! I hope I'm not giving bad info. Some of my style may be due to my driving a 2.5 so keeping it in the power band (3.2k+) is a job. When on the freeway I typically don't use 5th until above 75 indicated where I can keep in the aforementioned power band. That said in response to the OPs question regarding poor fuel mileage my thought is he is shifting just as he is entering the power band but more importantly may be spending too much time below the power band and in the lugging range of the engine with the knock sensor picking up the gears/chains lashing, then retarding ignition timing causing the poor fuel economy? If he is shifting 3.2 k then he is 2.2k after shift. OP lives in Monterey so as I'm sure you know it is not all sea level driving there. Viva Laguna Seca!:dance:

[JayG]

Originally Posted by 911monty

Hey JayG; Good to have an instructor chime in! I hope I'm not giving bad info. Some of my style may be due to my driving a 2.5 so keeping it in the power band (3.2k+) is a job. When on the freeway I typically don't use 5th until above 75 indicated where I can keep in the aforementioned power band. That said in response to the OPs question regarding poor fuel mileage my thought is he is shifting just as he is entering the power band but more importantly may be spending too much time below the power band and in the lugging range of the engine with the knock sensor picking up the gears/chains lashing, then retarding ignition timing causing the poor fuel economy? If he is shifting 3.2 k then he is 2.2k after shift. OP lives in Monterey so as I'm sure you know it is not all sea level driving there. Viva Laguna Seca!:dance:

Not an instructor (yet, maybe one day) but an enthusiast.

I don't see how shifting below 3.5 will reduce MPG. If anything running at higher RPM will decrease MPG. My 996 has a tip ( same tranny as 986 tip) and unless I am putting my foot into it, will shift right around 3k My guess is the tip in a Boxster will shift pretty much the same.

I would think that higher RPM = lower MPG n matter what gear or tranny you are using

[Giller]

I think OP should check his math. Based on what he has said, no leaks, no odours - it might just be bad math? 16 mpg is quite low. He hasn't answered Monty's question about total miles driven per/trip. If it's start, short drive then stop, that will impact economy more than anything really.