Is This Too Many Additional I/O For CAN bus?

[wes7143]

Hello all,

I am looking into aftermarket ECU options for my USDM 2005 Subaru STi and the Link G4X pnp looks like a good option. I have experience in flash-based tuning of the factory ECU, but am completely new to the aftermarket ECU tuning world and especially CAN bus.

One of the reasons why I want an aftermarket ECU is to accommodate additional inputs and outputs.

The recommended ECU for my car is the G4X WRX104X. This ECU looks like it will do the tuning part great, but the additional I/O is pretty limited through the expansion connector:

2004-2006 ECU 
The following expansion connector inputs/outputs are provided: 
Blank                AN Volt 11 
An Temp 4        Temperature sensor input 
Blank                No function 
Blank                AN Volt 12 
Blank                No function 
Blank                No function 
+5V Out        Low Current +5V Supply 
Gnd                Sensor Ground Only 

The G4X WRXLink (04) and WRXLink (07) Plug-in ECU has two CAN buses.

It looks like anything beyond one additional temp sensor and two 0-5v sensors will have to go over CAN bus.

I would like to keep all of the factory equipment in place in case I ever need to swap the factory ECU back in, so I don't want to delete anything to gain additional I/O.

Here is the list of all the extra junk I want the ECU connected to:

Additional Inputs:

• AEM Wideband O2
• IAT Sensor (additional)
• AEM Oil Pressure
• Fuel Pressure
• Coolant Pressure
• Exhaust Gas Pressure
• 4x Exhaust Gast Temp Thermocouples

Additional Outputs:

• Volvo Electric Power Steering Pump (CAN bus only), seems possible with G4X in this thread.
• Electric Water Pump for W2A Intercooler

Could someone look over this hypothetical setup and let me know whether or not it would work:

• AN Volt 11   <- AEM Wideband O2
• AN Temp 4 <- IAT Sensor
• AN Volt 12  <- AEM Oil Pressure
• CAN Bus 1  <- 4 Channel Analog to CAN Bus <- Fuel Pressure, Coolant Pressure, EGP
• CAN Bus 1  <- 4 Channel Thermocouple to CAN bus <- 4x EGT Thermocouples
• CAN Bus 2  -> Volvo Electric Power Steering Pump
• CAN Bus 2  -> CAN Bus to PWM Motor Driver? -> Electric Water Pump

 

Do I understand the situation correctly? Can I fit this much additional I/O through CAN bus?

[koracing]

The only real rule as far as I know regarding quantity with CAN is that anything on a particular bus needs to operate at the same baud rate, and all the AEM stuff is going to use 500kbps, and the Link can bus in the software only has up to 10 configurable channels for streams in or out.    It looks like both of your other devices you list for Bus 1 are also capable of operating at 500k.  Of course you'll also need to make sure you have a 120ohm terminating resistor at the end of the bus but both of your devices appear to have a built in terminating resistor that you can toggle on/off (only use 1).  So your can expansion device 4 channel most likely would be received on 1 stream (maybe up to 4 worst case), wideband on 1 stream, CAN EGT on one stream.

The wideband I would recommend using their X-Series wideband and placing that on using CAN 1 as well to avoid analog offset/drift issues.    

I'm not sure what your Volvo pup and water pump can bus speeds are going to need to be, but they would also have to be the same (and could also be on bus 1 if they were operating at 500k).  

Otherwise I think what you have proposed should work.  The math there for sorting out the CAN byte addresses for the 4 channel modle is a bit confusing for me, but I'm sure someone here could help once you get to that point.

[wes7143]

Thanks for your reply!

The AEM devices I have are both the older style (not X series). I was originally planning on using the 0-5v wires that come out of each gauge, but like you mentioned they do also spit out serial data that I could use instead.

I downloaded the file from the Volvo pump thread and it looks like it works fine at 500k.

[semih]

6 minutes ago, wes7143 said:

Thanks for your reply!

The AEM devices I have are both the older style (not X series). I was originally planning on using the 0-5v wires that come out of each gauge, but like you mentioned they do also spit out serial data that I could use instead.

I downloaded the file from the Volvo pump thread and it looks like it works fine at 500k.

 

 

i used older style aem wideband with g4x but it read wrong, i bought can lambda controller, for example can lambda controller read 13.4 aem read 12.2 i don't trust them

 

other than i'm using bosch combined pressure temp sensors for oil and fuel, i love them

[wes7143]

3 minutes ago, semih said:

 

 

i used older style aem wideband with g4x but it read wrong, i bought can lambda controller, for example can lambda controller read 13.4 aem read 12.2 i don't trust them

 

other than i'm using bosch combined pressure temp sensors for oil and fuel, i love them

So far I have had good luck with these sensors. I've been using the serial data with an old school serial to USB adapter into the laptop for logging with COBB or Romraider. I've always had good agreement between the factory O2 sensor, the AEM wideband gauge, and the logged AEM wideband data.

[semih]

10 minutes ago, wes7143 said:

So far I have had good luck with these sensors. I've been using the serial data with an old school serial to USB adapter into the laptop for logging with COBB or Romraider. I've always had good agreement between the factory O2 sensor, the AEM wideband gauge, and the logged AEM wideband data.

 

can lambda controllers faster than older wideband controllers, i was thinking the same as you, but i changed my mind after buying a can lambda controller.

[koracing]

If the analog output has a ground output as well, then reading it in via anaolog (or via your analog to can device) should work ok.  If your analog output doesn't have a ground output as well, then calibration can change over time which is less than ideal.

[wes7143]

So it sounds like I should have no problem fitting everything into CAN bus. Based on your suggestion, the setup would maybe look more like the following:

• AN Volt 11   <- Fuel Pressure
• AN Temp 4 <- IAT Sensor
• AN Volt 12  <- Coolant Pressure
• CAN Bus 1
  • Stream 1 <- AEM Wideband O2 (Serial Data)
  • Stream 2 <- AEM Oil Pressure (Serial Data)
  • Streams 3-6 <- 4 Channel Thermocouple to CAN bus <- 4x EGT Thermocouples
• CAN Bus 2
  • Stream 1 -> Volvo EPS Pump (Keep Alive)
  • Stream 2 -> Volvo EPS Pump (PWM)
  • Stream 3 -> CAN bus to PWM -> Electric Water Pump

I ditched the EGP sensor to fit everything without needing the 4 channel analog to CAN.

Does anyone have a good recommendation on a good budget CAN to PWM for controlling the water pump? I do already have a couple of solid state relays, but they need something to generate the PWM. I can't seem to find anything that is actually for sale that fits this purpose. Worst case scenario, I run the pump dumb, but ideally I'd like the ECU to control it based off of boost pressure.

[Adamw]

Note you also likely have these IO unused:

Inputs:  AN Temp 2 & AN Volt 8 in the MAF connector.  AN Temp 3 on pin C12.  AN Volt 4 & 5 in the TGV plugs.  AN Volt 7 in the rear O2 plug. 

Outputs:  Aux 7 & 8 in the TGV plugs.  Inj 7 in the 02 sensor plug 

[wes7143]

1 hour ago, Adamw said:

Note you also likely have these IO unused:

Inputs:  AN Temp 2 & AN Volt 8 in the MAF connector.  AN Temp 3 on pin C12.  AN Volt 4 & 5 in the TGV plugs.  AN Volt 7 in the rear O2 plug. 

Outputs:  Aux 7 & 8 in the TGV plugs.  Inj 7 in the 02 sensor plug 

Hi Adam,

This is true and would be good information for most users. However, I am too paranoid to delete any emissions related factory hardware. I would like to keep all that stuff in place and functioning so that I could quickly swap the factory ECU back in the event of needing to pass an emissions test in the future. My state does not currently do thorough emissions testing, but probably will in the future.

I also prefer MAF tuning to speed density. That may change once I start playing with a less janky ECU than the factory unit, though. In the past, I've played around with moving the one factory IAT sensor to a post-intercooler location for safer tuning, but it does make the MAF value less accurate since the temperature of the air at the MAF is part of the quantitation. So ideally with the G4x, I'd like to have two IAT sensors - one to help the MAF MAF, and one to help me not blow up the motor.

[Adamw]

We dont currently have a proper MAF based fuel strategy, although you can make it work, I wouldnt bother.  

[koracing]

I don't think you can make gauge serial output data work as an input on the CAN bus to read o2 sensor data or oil pressure data - maybe @Adamw can confirm?