Code: EGR and CTS conversions

[1project2many]

1project, what ECMs are we talking about?

I can tell you that the 7148 (A C3) and 7783 (also a C3) uses the dual pull up setup. If you go here:
http://www.aces.edu/~parmega/efi/inside7747.htm there are links to pictures of both types of circuits for visual confirmation.

This whole thread is 1227747 $42 for now.

Makes it easier, but still... who wrote some of those disassemblies? Where did they get the temp conversions? Can you say for sure someone didn't copy the wrong info because they had no idea it was wrong?? Maybe not now but after you're done with this I'll bet yes.

The others I looked at were $4E, $4F and I forget, but all the same C3 type ECM, none of which had IAT.

I wonder how hard it is to identify the code that handles the switch from one resistor to another. That would be a sure way to know what you're working with. Maybe it's as simple is identifying the shape or curve of the conversion table(s)?

When it looks like now they did not need a conversion at all?

You know, some of these guys had actual GM data in hand when they did this. For example, the commonly found GM P4 turbo document has this information:

2.4.1 Coolant Temperature
Due to the nature of the transducer interface configuration and the characteristics of the
temperature sensing thermistor, the A/D conversion is non-linear with coolant temperature.
ROM tables *FCLT348* and *FCLT4K* linearize coolant temperature to provide a coolant
range from -40 to +152 Deg C (3/4 of a degree per count).

So the raw A/D counts cannot be converted with a simple formula, but there is a math conversion for the eight bit value that represents coolant temp after the table lookup. And since most of the gmecm's I've worked on report CTS within roughly the same range, it's hard to imagine using any other formula for an eight bit value. The actual conversion from a GM paper is N = (E + 40) * 256 / 192.

Now you need to know if you're using values that represent raw a/d temp or linearized temp. The note "1K p/u" is the author's way of distinguishing the two. Three different datastream definitions for the L05 use the same chart of A/D to CTS values and based on the values it appears that inverted CTS is output on the ALDL. Is this how the conversion is set up for the scanner part of TP? If not, then the values you see when testing may not be correct. If you're monitoring events using ALDL data and you're unsure of the temp conversion, use the hex values. You'll be able to make a direct comparison between programmed and sensed temp and you can often tell if you're testing a linearized value vs a raw a/d count value.

I think I'm going to stop here for now. The kids are up and active and I don't get more than three minutes of clear thought before I have to go resolve one conflict or another.

HTH.