Resistance to Voltage Converter for Gen 3 ECU Logging

jlvaldez
Posts: 155
Joined: Mon Feb 11, 2019 12:48 pm
cars: '01 - Corvette Z06
'20 - Sierra Denali
'03 - Volvo S80 T6
'16 - Accord V6
Location: DFW, Texas

Re: Resistance to Voltage Converter for Gen 3 ECU Logging

Post by jlvaldez »

Good to know! Maybe I should scale this board up and support other forms of input....

EGR is something no one interested in this kind of thing would ever likely use.

So then depending on the level of "race car" you could use:
AC - Sometimes
EGR - Almost always
Secondary O2s (2 channels, almost always)
kur4o
Posts: 948
Joined: Sun Apr 10, 2016 9:20 pm

Re: Resistance to Voltage Converter for Gen 3 ECU Logging

Post by kur4o »

Speaking of different sensors, there is generally 2 types. PCM output 5v on the pin->the sensor through internal resistance brings the output to 0v. Something like 5-0v. Usually you can`t feed voltage output on that kind of sensor pin.

Second type is pcm sends solid 5volts to sensor-> sensor use it as a power supply and through some conversion sends back to pcm 0-5v on another pin, that can sense 0-5v input. On that kind of input you can feed 0-5 volts.

There is also another input that uses frequency modulated signal , but that is not on the subject right now.

ON each pcm I have reversed the board, there are some unused pins, free a/d channels that are not used in software but are mapped and can be patched to whatever you like. Finding these is not easy, and also tracing the ram a/d address is the hardest part but can be done.
bubba2533
Posts: 498
Joined: Wed Apr 11, 2018 8:50 am
cars: 03 Chevy S10 Turbo V6

Re: Resistance to Voltage Converter for Gen 3 ECU Logging

Post by bubba2533 »

kur4o wrote: ON each pcm I have reversed the board, there are some unused pins, free a/d channels that are not used in software but are mapped and can be patched to whatever you like. Finding these is not easy, and also tracing the ram a/d address is the hardest part but can be done.
If you have the PCM pins I can find the a/d address for them quite easily.
LS1 Boost OS V3 Here. For feature suggestions post in here Development Thread. Support future development ->Patreon.
kur4o
Posts: 948
Joined: Sun Apr 10, 2016 9:20 pm

Re: Resistance to Voltage Converter for Gen 3 ECU Logging

Post by kur4o »

I can`t believe nobody mapped all the pins of p59 already.

We need some complete chart of what is already known from all platform schematics, and than start hardware hacking.

5volts pins can be easily found. Apply power to pcm and test each pin for voltage output. Than test for negative voltage each pin. Than remove power and test each pin for resistance to ground. Than some data analysis with pattern finding can bring down suspect pins to couple that can be traced on the board.

Here is some excellent hardware reverse engineering of 97 lt1 board.
http://www.gearhead-efi.com/Fuel-Inject ... F-Body-ECM
Pretty sure there will be lots of similarities to p59 board.
jlvaldez
Posts: 155
Joined: Mon Feb 11, 2019 12:48 pm
cars: '01 - Corvette Z06
'20 - Sierra Denali
'03 - Volvo S80 T6
'16 - Accord V6
Location: DFW, Texas

Re: Resistance to Voltage Converter for Gen 3 ECU Logging

Post by jlvaldez »

That's actually a very interesting idea. However I'm assuming that AD pins are NCed on the PCB and we would have to blue wire the MCU pins to the PCM connector, no?

And then we would even need to figure out how to schedule the sampling in to the OS and assign a PID to it so it could be polled via OBD?
jlvaldez
Posts: 155
Joined: Mon Feb 11, 2019 12:48 pm
cars: '01 - Corvette Z06
'20 - Sierra Denali
'03 - Volvo S80 T6
'16 - Accord V6
Location: DFW, Texas

Re: Resistance to Voltage Converter for Gen 3 ECU Logging

Post by jlvaldez »

Well i finally connected it up to my bench ECU to start testing it. 3D printed a little box for it.

Turns out the O2 signal and ground reference are isolated. So i need to ground the O2 low references to the output to get any data.

Checked for any biasing circuit that might cause issues shorting low ref to ground and see no DC current generated. So it should be safe to simply ground the HO2S low references for the secondaries to ground.

Edit: Finished connecting and testing on the bench ECU. So a few things to note:
1) The O2 sensor's low references are isolated and not by default referenced to anything. You must supply the low reference, and it is not internally connected to ground.
2) The O2 ADC seems to sample up to 1.107V where it caps out.
3) Hard to say for sure the resolution since there are 2 PIDs that HPT shows. One (2 byte PID) gives 0.005v resolution. The other (1 byte PID) gives 0.004v resolution.
4) There does not appear to be any form of filtering on the O2 input, as it bounces around a lot even on a bench harness. The noise is basically 1 step/lsb of resolution.
5) The internal 450 mV bias on the input pin does not appear to source or sink any current, so this leads me to believe they're using an op amp to buffer in the input with a biasing network.
PXL_20221129_212238048.jpg


I also was able to grab the PIDs and do some sniffing to figure out the conversion. It's very strange. 0x00 = 0V. 0xFF = 1.107 V.
IMG6311034210276045552.jpg
jlvaldez
Posts: 155
Joined: Mon Feb 11, 2019 12:48 pm
cars: '01 - Corvette Z06
'20 - Sierra Denali
'03 - Volvo S80 T6
'16 - Accord V6
Location: DFW, Texas

Re: Resistance to Voltage Converter for Gen 3 ECU Logging

Post by jlvaldez »

On track yesterday, today and tomorrow in the new setup for my C5Z testing this box. It works great. Surprisingly well honestly.

Fwiw the setup is a 2001 Corvette. 468 stroker with factory ECU. Dailey dry sump and and trans/diff coolers.

This box was used to log temp data using these extra channels.
Post Reply