I have the AutoTap and I've
 

I have the AutoTap and I've used it extensively to diagnose problems with my car and also just to gather data under measured conditions to make accurate judgements about gas mileage using conventional motor oil and synthetic motor oil. Guess what? Under identical conditions, you get the same gas mileage with synthetic as you do with conventional motor oil.

I agree, the AutoTap is fantastic. You can log lots of different parameters and replay the data after a run. The logs are exportable to a spreadsheet-readable format also so you can chart and graph whatever you want however you want to make sense of the data. The more parameters you log, though, the lower the sampling rate becomes, so you have to choose wisely what you want to see if you want to gather the data frequently enough to capture the specific condition you need. The software that comes with it will allow you to replay a sample through the logs, graphs, and gauges that you set up yourself, so the display is fully customizable with all the data that's available to you. Pretty cool to tinker around with, and it can save you a bundle in diagnostic fees if you have problems with your OBD-II equipped vehicle, which is any vehicle 1996 or newer.

Re: I have the AutoTap and I've
 

care to share details of your methodology & results (maybe start a new thread)? i for one would find that very interesting.

Re: I have the AutoTap and I've
 

Ditto

Here you go.
 

oopsie, duplicate.

Here you go.
 

Good old college memories...

The gist of it is we duplicated as many factors as we could control, with environmental conditions being the most difficult and costly of those. Humidity, temperature, and even barometric pressure were duplicated as closely as possible. We changed the oil between Pennzoil 10W-30 and Redline 10W-30 in a Cadillac with a 4.6L V-8 engine. The mileage figures were so close as to be almost statistically insignificant. The Redline showed a mileage increase of 0.21% (22.059 MPG versus 22.105 MPG). Two of the runs were slight advantage to Redline and one was slight advantage to Pennzoil, so you can judge that for yourself. The advantage probably comes from the short duration that the synthetic oil is slightly less viscous than the conventional oil. There were factors we did not duplicate, such as cold weather and hot weather. We started at 75*F oil temperature and stopped after 20 minutes of varied and identical "driving" conditions on a dynamometer, 3 times with each oil. During the runs, the PCM stayed in "open loop" mode for almost the exact duration, within less than 10 seconds, fuel trim rates on the AutoTap log files showed almost identically, MAF rates showed almost identically, ignition advance showed almost identically, and coolant and oil temperatures rose almost identically. We used the AutoTap to graph that kind of information so we could better gauge the accuracy of our results. A special adaptation was made to the car's fuel rail by my nerdy friend Jason so we could insert flow rate meters on the delivery and return lines to accurately gauge fuel consumption. When we were done, that fuel rail was removed and discarded for safety reasons. The AutoTap was used in conjunction with the dyno logs and the flow rate meters and the oil temperature meters were handled by separate devices because that car didn't have an oil temperature sensor. A Fluke meter with a printer gave us the oil temperature information, and the flow meters were wired to some kind of device made by HP, but Jason the nerd took care of that part so I don't have any details on what it was or how it worked. All I know about it is that we paid a lot of money to use it.

We did a total of 8 oil changes on that car, and at 7.5 quarts for each change, we racked up a huge bill for Redline oil (almost $200).

Time for my vacation. There are some reefs (and other things) in Australia that I've been wanting to see. I'll be back in a few weeks. In the meantime, discuss amongst yourselves.

Re: Here you go.
 

Enjoy yourself!

nice summary - thanks for
 

nice summary - thanks for the reply.

Question - when I get my
 

Question - when I get my Hondata installed, do you think comparing the areas under the curve from the injector pulse width graphs would be a good measure of fuel consumption? This could be done in short or long things... A short thing would be tesing whether driving at WOT in 5th is better than light throttle [is reducing pumping losses outweighed by a larger injector pulsewidth?].

Things like this I really can't wait to test out.

i'm no expert, but it sounds
 

i'm no expert, but it sounds like a good method to me. if you can log injector pulses accurately, you're effectively logging fuel used, aren't you?

I suspect this is exactly
 

I suspect this is exactly how Scangauge works. Just because a car is OBD2 equipped doesn't mean it has flow meters on the fuel rail. I don't see how else you'd know fuel consumption other than injector pulses. Being that a typical injector pulse is on the order of a couple milliseconds, a PIC microcontroller with a 4MHz clock is capable of executing 1,000 instruction every millisecond, so you can effectively measure each pulse +/-0.001 ms, in other words, very accurately.