Thread: Tuning for Gas Mileage

ScanGauge II that connects to the OBDII port. It's kinda nifty. It takes about 30 seconds from cold start for the Plano type O2 sensors to enter closed loop, while thimble styled O2 sensors take about a minute.

Just got back from my trip and have some positive numbers.

Going at 65 MPH I got better gas mileage then at 70MPH (expected), but going 65MPH I also got better gas mileage then 55-60MPH.

It was hard to have similar driving conditions for the whole trip, it ranged from crappy construction roads on the highway, to stop and go traffic.

Average MPG at 65mph yielded me 31-32MPG. At 70mph my average MPG was 30-31. I setup my ScanGauge II to read the numbers accurately, and it was down to the tenth correct of what my MPG would be at the pump. This is how I saw that my MPG was better at 65mph.

Anyway, what has changed was, TP table was setup to not be in the last two columns on even slight throttle. Thus the car did not go into boost as much or got 10-12 AFR's while just cruising.

My tire pressure is at 38 Front, and 34 back. Usually my tire pressure would be at 35/33, but I've done as much as 40psi in the front with no gain.

I also Updated my timing table to have a little more timing in the commonly traveled parts of the map.

And lastly, I noticed that with cruise control I'm loosing a good bit of gas mileage going down the hill. Cruise Control tries to keep the throttle open and O2 sensor keeps the AFR's at 14.7 thus going down hill I would get 60-70 MPG, when just in gear without cruise I would get 180-200mpg.

This is very interesting for us with widebands! To have the wideband autotune in closed loop will be great.

The E-Manage Ultimate also has an autotune feature that leaves the AFR close to what you want as a starting point. It only worked in open loop though as the closed loop ECU adjustments wouldnt let it work down low and mid ranges.

As far as I understand, Cruise Control is only efficient in an ideal long straight highway with no ups or downs. Everywhere else it will lose extra gas.


So what AFR you shoot for while still in vacuum? 14.7? And what about on low boost 1-5 psi?



What did you do here? up the timing a bit?

I know this is long overdue, I somehow missed it .

Either way bringing this from the dead, I'm going to start this back up now that my car is drivable again .



That's correct .



This is what BenFenner suggested to me, and it makes sense, but please use at your own discretion .
14.7 under slight load (cruising), 12.8 at WOT before boost. In low boost applications, 1-4 psi, about 12.3-5, 5-10psi 12.0:1 or richer.



I added more timing in the common cruising speeds.