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  #46  
Old 05-21-2007, 06:03 AM
ItsPeteReally ItsPeteReally is offline
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You can take things a little too far in the search for accuracy

Without knowing anything at all about the ECU I think we can safely surmise that the TPS voltage read by the ECU is unlikely to be used to access a myriad of subtly different lookup tables. I'd be very surprised if the TPS output was interpreted as being any more than the equivalent of none, a little, some, a lot, and maximum, which would call for five different mappings (and I suspect that this is too many!).

Similarly, I would venture that other voltages are only significant to the CPU when they cross certain threshold values.

Most inputs can be categorised as rich/lean, cold/hot, etc.

I don't dispute that the input values are readable to quite high degrees of apparent accuracy but I have my doubts as to the dependability of the calibration behind them.
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  #47  
Old 05-21-2007, 09:24 AM
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Quote:
Originally Posted by ItsPeteReally
I'd be very surprised if the TPS output was interpreted as being any more than the equivalent of none, a little, some, a lot, and maximum, which would call for five different mappings (and I suspect that this is too many!).

Similarly, I would venture that other voltages are only significant to the CPU when they cross certain threshold values.
You make a lot of sense. The accuracy is within tolerance whichever way it's calculated.
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Last edited by b3lha; 05-21-2007 at 09:50 AM.
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  #48  
Old 05-21-2007, 09:31 AM
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I haven't made much progress in decoding the ECU of late. The problem is that I don't understand enough about how the ECU is supposed to work in order to understand the meaning of the calculations I'm looking at. It's complicated and it will take some time to figure out.

However, this weekend I discovered how to download the TCU . I have managed to dump it to a file and disassemble the code. This looks like it could be an easier job to tackle. Details on my website. http://www.alcyone.org.uk/ssm

Phil.
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Last edited by b3lha; 05-21-2007 at 09:38 AM.
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  #49  
Old 05-21-2007, 02:40 PM
Trevor Trevor is offline
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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.
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  #50  
Old 05-21-2007, 07:31 PM
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Quote:
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.

Phil.
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1992 Alcyone SVX Version L
1994 Alcyone SVX S40-II
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Last edited by b3lha; 05-22-2007 at 02:12 PM.
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  #51  
Old 05-21-2007, 07:50 PM
Trevor Trevor is offline
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Phil,

You are spot on in my book. Percentage is the operative word for sure.
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  #52  
Old 05-21-2007, 08:13 PM
Trevor Trevor is offline
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Quote:
Originally Posted by ItsPeteReally
You can take things a little too far in the search for accuracy

Without knowing anything at all about the ECU I think we can safely surmise that the TPS voltage read by the ECU is unlikely to be used to access a myriad of subtly different lookup tables. I'd be very surprised if the TPS output was interpreted as being any more than the equivalent of none, a little, some, a lot, and maximum, which would call for five different mappings (and I suspect that this is too many!).

Similarly, I would venture that other voltages are only significant to the CPU when they cross certain threshold values.

Most inputs can be categorised as rich/lean, cold/hot, etc.

I don't dispute that the input values are readable to quite high degrees of apparent accuracy but I have my doubts as to the dependability of the calibration behind them.
I am confident that set points or calibration to a known value/figure will not be involved, and as you state there will be no apparent accuracy based on any specified criteria.

I think Phil has it right in considering the reading/indication/signal, always in terms of a percentage. As you say a percentage of between none and maximum and not as a specific measurement of a quantity/value/'position/whatever.
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  #53  
Old 05-26-2007, 01:45 AM
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Phil!!! I found something really interesting while perusing the TSB page linked in the General forum... it's a whole TSB about communicating with the Cruise Control Computer through the select monitor!!! Uploaded it to my locker for ease of access.

http://www.subaru-svx.net/photos/fil..._Wan/44146.pdf

Hopefully it will help somehow.
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  #54  
Old 05-26-2007, 07:50 PM
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Quote:
Originally Posted by Nomake Wan
Phil!!! I found something really interesting while perusing the TSB page linked in the General forum... it's a whole TSB about communicating with the Cruise Control Computer through the select monitor!!! Uploaded it to my locker for ease of access.

http://www.subaru-svx.net/photos/fil..._Wan/44146.pdf

Hopefully it will help somehow.
Good find Nomake! Thanks!

It corroborates what I found in the service manual. Actually, your post inspired me to do a little more investigation on the cruise control unit and I found something rather puzzling. The TSB you found says that the cruise control master switch must be turned on.

The unit that responds to command "89", sends responses even when the cruise control master switch is off. And the data doesn't change when I wiggle the cruise engage lever. So it probably isn't the cruise control unit sending the responses.

Heaven knows how you get the cruise control unit to respond, I've tried every command from "00" to "FF" and the only ones that respond are 78(ecu), 45(tcu) and 89. There is an extra wire in the select monitor plug that goes to the cruise control unit, so I reckon that you have to do something with that wire to get data from the cruise control.

The other question is, what unit is responding to command "89". I thought that the only units connected were the ECU, TCU and Cruise. So I had another look at through the (USDM) wiring diagram and found that the Aircon unit is also connected. So I turned the Aircon panel off, but the unit still responds, so it's not the Aircon either - Unless the Aircon controller is still powered when the control panel is turned off.

I can't think what else it could be. The other thing I noticed is that the mysterious unit 89, stops responding when the engine is running. It only talks to the select monitor when the engine is off, but the ignition is on.

It's a mystery to me.
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Last edited by b3lha; 05-26-2007 at 07:53 PM.
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  #55  
Old 05-26-2007, 08:02 PM
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I notice that there is a genuine Subaru Select Monitor on ebay uk at the moment. Rather pricey though at 600 pounds. It is, after all, 10+ years old and pretty much obsolete. There aren't enough old scoobies around to justify a garage splashing out it. They would only use it once in a blue moon. And it's too expensive for car enthusiasts like us to even contemplate.

I offered him 60 for it, but he turned me down.

http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=200112707128

He doesn't mention whether he has the SVX cartridge for it or not.
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Last edited by b3lha; 05-27-2007 at 07:18 AM.
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  #56  
Old 05-26-2007, 08:13 PM
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Actually, you might be right with your initial guess.

The cruise control computer turns off when you turn the switch off.

The Zexel aircon unit doesn't.

Now, I'm just guessing at this point... but remember you can hit the "Outside Temperature" button when the Zexel unit is "off" and it will still display the temperature and beep as it should. To be able to do this, the computer would have to be on, would it not?
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  #57  
Old 05-27-2007, 06:51 AM
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Quote:
Originally Posted by Nomake Wan
Actually, you might be right with your initial guess.

The cruise control computer turns off when you turn the switch off.

The Zexel aircon unit doesn't.

Now, I'm just guessing at this point... but remember you can hit the "Outside Temperature" button when the Zexel unit is "off" and it will still display the temperature and beep as it should. To be able to do this, the computer would have to be on, would it not?
You're right!

I did some more investigating. The data returned by command 89, changes when I press the buttons on the A/C panel. So that proves it. I even managed to figure out what some of the values mean and I've updated my website accordingly. http://www.alcyone.org.uk/ssm/acu

Phil.
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  #58  
Old 05-27-2007, 04:44 PM
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Have you seen the technical information video on the Zexel aircon unit, on the SVX User DVD that's on eBay? It has a ton of information on how the computer functions. Very useful... well, just for learning how the compressor works and how to use the Debug mode, for me... but it'll probably have lots more info for someone who's trying to disassemble the code!
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  #59  
Old 05-28-2007, 04:57 AM
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Quote:
Originally Posted by Nomake Wan
Have you seen the technical information video on the Zexel aircon unit, on the SVX User DVD that's on eBay? It has a ton of information on how the computer functions. Very useful... well, just for learning how the compressor works and how to use the Debug mode, for me... but it'll probably have lots more info for someone who's trying to disassemble the code!
I haven't seen the video, but my Japanese aircon is a little different to the USA system at least in terms of the user interface.

Unfortunately, there doesn't seem to be a way to get the program code for the aircon unit. The system just returns a few bytes of status information for the select monitor. I don't think it will be too much of a problem to figure out the meaning of these status bytes. I've got some already, like the temperature setting, outside temperature, button pressed and fan speed.

I had quite a productive evening yesterday. I figured out how the ECU stores trouble codes, which gives me a bit more insight into some of the variables. For example, having found the piece of code that flags a sensor error, I know that the code that processes that sensor must be nearby. I also discovered that my car does not have any code to set the Atmospheric sensor error, AF Learning error, or any of the EGR errors. I guess these errors are specific to the emissions system on the USDM model.

I also found the code in the TCU that decides whether to use the normal map or the power mode map. I was thinking that it might be possible to change the variable and thereby switch power mode on through software. But it's not that simple because the TCU recalculates the variable 25 times a second. Then I discovered the timer that determines how long power mode stay on once you ease off the pedal. I was thinking that if I keep resetting the timer over and over, and never let it timeout, then power mode will stay on permanently. The theory is good, but at present it's not working in practice. I need to study it some more and see where I'm going wrong.

Phil.
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  #60  
Old 05-28-2007, 07:45 AM
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Quote:
Originally Posted by b3lha
I also found the code in the TCU that decides whether to use the normal map or the power mode map. I was thinking that it might be possible to change the variable and thereby switch power mode on through software. But it's not that simple because the TCU recalculates the variable 25 times a second. Then I discovered the timer that determines how long power mode stay on once you ease off the pedal. I was thinking that if I keep resetting the timer over and over, and never let it timeout, then power mode will stay on permanently. The theory is good, but at present it's not working in practice. I need to study it some more and see where I'm going wrong.

Phil.
Hi Phil

Good work on the data breakdown so far.

Regards the Power mode, you know we have had long discussions about this, and the only one that we know to actually work as an override is a pulsed voltage to I think the TPS input.

Your breaking down of the software inside the TCU may well lead to better or less complicated permanent switching, which would be great!

If you think the OZ WSM for the gearbox might be useful, I'd be happy to post it to you, and collect at JAE.

As regards your point above with the timer, the complication could be the speed signal, as Power mode shift map is put in place by two variables, throttle position and road speed. The following is how the WSM describes the drop back to Normal:

The power pattern is shifted to the normal pattern depending on car speed. Shifting to the normal pattern is determined by the throttle position as shown in the figure on the right. Time lag in shifting [from power to normal] is also determined by car speed. The maximum time lag is 3 seconds.

The diagram is a simple Venn diagram. Judging by the relative areas shown it would be reasonable to presume that Power will drop off [on cutting back throttle opening] after 3 seconds at lower speeds, after 2 seconds at mid speeds, and after 1 second at high speeds. I expect low, mid and high speeds are preset at specified ranges within the firmware.

This in turn leads me to believe that you may have more success holding power mode in the software by "fooling" it into seeing an open throttle all the time in the TCU software, rather than changing the timed drop-off interval.

The ECU will still operate as normal on the real and actual TPS input signal. The shift map changover for the TCU needs to see WOT all the time to hold power mode all the time.

Joe
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