Jeep 4.0 Volumetric Efficiency

[BBeach]

Just filled up today and got 20.5mpg with mostly (85%miles) at 55mph and the rest on trails (think of it as rough city driving). It almost brought a tear to my eye to see 20+.

 

[scottbky]

Idle in D, or coast in D. I think of idle with the brake on or under 5 mph. Even rolling at 30 or 40 in D, foot off the gas ign goes to 14. Idle in N = idle in P. Saw some other thread (can't remember where) about 12 being the most geometrically efficient. RPM's are higher with higher speed in an auto; not really idling when off the gas.

ScottB

 

[MaXJohnson]

Thats interesting about the MPG, having the conflicting results of MPG dropping after 55 or 65:

The ignition timing was also interesting, thanks for collecting that data. I had just assumed that max advance was 36, but it appears its as high as 42 under lean cruise as you stated. Two areas at important, the lean advance for maximum MPG under cruise, and a under full load(low vacuum , high RPM). Can you log advance, at some reasonable refresh rate? It would be interesting to see a WOT run, what advance it maxes out at, and how soon it reaches that max. I'm guessing 32 degrees at maybe 3000 RPM, mind if you get a change, checking that out?

I made lots of progress on my computer, but it will have to wait until this semester is over until I can do more work on it. I going to made a circuit to input the VSS(vehicle speed sensor) to my computer(MegaSquirt) so I can figure out gas mileage. I need a frequency to voltage converter IC, which I will have to order. Then I can start posting finds of my own.

This is really interesting stuff

here's some data that might put a smile on your face:

MPH, RPM, Throttle Position, MAP and Timing data in table form based on my 13 mile trip to work(stock 97 auto). 2 1/2 miles on city streets followed by 10 miles on the freeway with the first half in heavy, slow traffic. Another 1/2 mile of city street driving after the freeway. Sample rate is at 6 second intervals. Note that the throttle position is a % of travel with 15.69% being closed throttle blade and WOT at around 75% to 80%. MAP is in psi. The speedometer reads a percent or two on the high side. This particular trip would yield a trip average of about 18MPG.
http://home.everestkc.net/alynloya/97XJ_home_to_work.htm