View Single Post
Old 05-21-2007, 06:31 PM
b3lha's Avatar
b3lha b3lha is offline
Phil & Belha
Join Date: Aug 2001
Location: Alcyone Limited, Buckinghamshire UK
Posts: 2,671
Originally Posted by Trevor
Hi PHil,

I have just typed up thoughts with a view towards posting. Having opened the thread I find that there are other rather confirming comments. This is indeed interesting and I would say conclusive.

Further overnight thinking:-

The concept of “learning” as applied to computer controlled activity, has always eluded me in as far as being a proper description. No sensor in the automotive area can be expected to have intrinsic accuracy on the basis of manufacture or life expectancy. Learning as such, would require massive memory.

This aspect does not present a problem provided all devices are employed as providing a means of proportional output. There are means to this end and the advent of the op amp IC is one. The use of this principle would provide the so called “learning” aspect.

On this basis all inputs after interfacing, could be finally become evident as divided into increments of 5 volts, or -5 through +5 volts and 10.

In the application of the TPS, an applied voltage of five would be readily available in regulated form, but could not remain static as a result variables within the TPS and wiring, as is indicated by the test tolerances quoted in the manual. However as a proportioning device applied across a 5 volt circuit the resulting output would be accurate and remain as such.

I am in the dark here and am groping on the basis of logic. The idea is to provide the ideas you have requested, so as to promote further possible research.
Hi Trevor,

I'm afraid I don't have enough electronics knowledge to understand everything you are saying here, although I think I get the general idea.

However, having thought about it some more, I think that the actual voltage is irrelevant - it's just a means to an end. The ECU actually wants to know how open the throttle valve is. The TPS measures this, some unknown magic happens and the ECU ends up with a number between 0 and 255. Think of it as a percentage except it goes from 0 to 255 instead of 0 to100. So if the number is 0, the throttle is 0% open, if the number is 255 the throttle is 100% open.

The only reason I mentioned the TPS was to highlight that the pioneers in this area have differing opinions on how to decode the data. Maybe I should have cited the knock correction as a better example, where the vwrx software outputs the number from the ECU whereas the Legacy software decodes this into degrees of retard.

It has occured to me that one way to find out more about the ecu would be to trigger some check-engine codes and see where in the memory they are stored. Then look for the line of program code that stores them. For example, the line of code that stores code 32, must be part of the subroutine that processes the signal from the Right O2 sensor and the line that stores code 21 must be concerned with the water temperature sensor. That's my theory anyway, I'll have to see whether it works in practice.

Subaru ECU and TCU Website
1992 Alcyone SVX Version L
1992 Alcyone SVX Version L
1994 Alcyone SVX S40-II
2004 Subaru Legacy 2.5 SE Sports Tourer
1996 Subaru Legacy 2.2 GX Wagon
1988 Subaru Justy J12 SL-II

Last edited by b3lha; 05-22-2007 at 01:12 PM.
Reply With Quote