Been working on problem related to the GM ADC or A/D converter function used by GM ECM's.
Simply wanted to relocate the IAT sensor for my E60 [LLY Duramax] ECM from the combined MAF/IAT unit to the intake runner so it gives a true air temp reading after the turbo and charge cooler. What should be an easy mod has had me racking my brain because the ohms to temperature scale of the different IAT sensors don't match up.
EFIlive gives tuners the ability to modify all sensor scaling. However, GM uses a micro-controller with split "2" resolution scales for each sensor. So we have have a non-linear resistance scale sensor, that is converted to a voltage by a split resolution controller. One scale for hot, other for colder temps, that overlap and the ECM switches them on the fly.... Plus it uses the 10 bit sampling rate scale rather than voltage or resistance levels vs temp.
When I brought this up on the EFIlive forum looking for answers, without a single reply, I knew it was gonna take some research. To a layman, the electrical engineering design or workings of the A/D controller is quite confusing, but I'm slowly understanding it.
Attached is what my "stock" scaling looks like. I have the "ohms of resistance to temp" scale of both IAT sensors. Thanks to EagleMark's explanation on here, I've learned that the GM controller uses a dual 348/4000 ohm Bias resistor to split these scales. I verified this info by using a handy ADC Count Converter in the Megasquirt Manual ..
For the detailed definition on these micro-controllers, see this Berkeley University ADC Explanation PDF
So besides mapping both IAT ohm/voltage conversions manually for each 10 bit step, is there any tools or spreadsheets out there that could be used to convert C or F temp scales directly into that 0-1024 table that GM uses?? I've found the formulas, but am not that good in Excel to start on it from scratch.
Reply With Quote
Bookmarks