Using the "Engine Load" number from OBDII...

[root]

I just got a scangaugeII, and the most interesting feature to me is the engine load information it reports (LOD) as well as the throttle position (TPS)

somehow the ECU calculates the percentage of available power being used, from the fuel / air ratio, the intake temp, the RPM, the throttle sensor and so on.

I understand the general technique is to use full throttle at low RPMs with early shift points, but I would like to go a step beyond, perhaps figuring out the LOW cutoff on the RPM range, and how to quickly discover it from the information available.

Now, I can setup a long long set of experiments to figure which combination of throttle inputs and the shift points will yield the best MPG results, but I am wondering if anyone has come up with rules of thumbs that can teach me the techniques using the following ScanGauge information:

Throttle position -- TPS
Engine load -- LOD

Please point me to any info that will help me make sense of this extra information available to me.

(car info -- 2005 mazda3 2.3L, 2000 toyota MR2 1.8L, both MT)

[Bill in Houston]

high throttle openings may cause enrichment, which would be bad for FE. something else to experiment on!

[skewbe]

Good point Bill.

Your scanguage has an "open loop" monitor you can set that might tell you when enrichment kicks in, it does on my metro anyway. And it isn't quite full throttle, more like 2/3, or just before enrichment would be good if you can get a feel for that.

[Bill in Houston]

Originally Posted by skewbe

Your scanguage has an "open loop" monitor you can set that might tell you when enrichment kicks in,

Cool tool.

[Bennet Pullen]

I also find the loop gauge (LP) quite helpful. On my car it also goes into open loop when the fuel is shutoff while coasting in gear. There is no standardized way for OBDII to transmit that data but the loop can show it depending on your car.

My favorite use for the LOD gauge is to tell me when to coast. If you sit in neutral and rev your engine to different RPMs you will notice that while the TPS will change the LOD will not. For me it stays at a constant 27. Because of this I know that if I ever see my LOD at 27 or under while driving that I can coast without loosing any speed.

[bobski]

Open and closed loop operation can be judged with a relatively inexpensive air/fuel ratio gauge. It's simply a 0-1 volt meter (bar-graph, generally) that connects to the oxygen sensor. In closed loop, the value bounces back and forth, in open loop it just jumps to rich.
I bought a cheapie sun-pro gauge for around $30 a few years back, Summit sells their own branded gauge for a similar price... More prominent brands such as autometer run about twice that. A/F gauges are generally compatable with any car using a narrow-band oxygen sensor.