CAN wideband.

[Steve Bull]

I've got AEM wideband O2 sensor that I believe has the capability of transmitting on CAN. Now I was trying to find out what the advantages of using CAN rather than a 0-5v input. I know it will free up one input, that could be used for something else, other than that is there any other great advantage. I'm presently at that point of the final fit my ECU and getting/cutting all the Looms to fit the ECU, I realised it if it do go down the CAN route for the Wide Band that i have  to somehow incorporate it into the system or get a CAN extender.

 

[Adamw]

CAN is a digital signal - just 0's & 1's going down the wire.  This means the ecu always receives exactly what the controller is outputting.  With an analog output the controller outputs a voltage in reference to a common (or sometimes not common!) ground. Very few wideband controllers have a differential ground completely isolated from power ground, so even if they have a dedicated analog ground, there is still an influence from load on the power/chassis ground.  Any offset between the ground the wideband is referencing compared to the ECU ground reference will offset the measured signal.  You can usually observe this with an analog controller by for example turning on the fan or head lights and you will see the reported AFR change.  Some of the cheap ones you can even see the wideband heater turning on and off in the analog signal.  A further issue is most of them have a very poorly calibrated DAC - i.e the documentation may say for example it outputs 2.5V at 1.00 lambda, but if you test it you find it is actually only 2.3V. 

[Steve Bull]

Right, be worth doing then. will it be fine to run it with a Link CAN splitter.

[Adamw]

2 hours ago, Steve Bull said:

will it be fine to run it with a Link CAN splitter.

You will only need a splitter if you want to connect more than one CAN device.  

[Steve Bull]

Yes, running a dash as well. Admittedly it’s a Haltech one.

[koracing]

Anything on the same CAN bus needs to be running at the same bit-rate.  The AEM wideband will run at 500kb/sec.  The Haltech dash is probably 1Mbit/sec so you'll have to use a second CAN bus.

[Adamw]

Haltech dash has configurable bitrate, they are fine on the same bus.  

[Steve Bull]

Ive just see the reply, yeah thanks for that .  Ive seen that the Haltech dash can be set at 500kb/sec so both will be  running at the same bit-rate. Shortly I will be running a PDM and the associated can keyboard hopefully these can be set to 500 kilobytes second. For receiving and sending data to the PDM (which is looking like it will be a hard wire electronics one) what's the best setting to have just send/receive configurable generic dash.

[Adamw]

You would generally do a custom setup at both ends for a PDM.  Typically there is not much needed, usually just things like a fan and fuel pump request and maybe a button status or two from the keypad.   

[Steve Bull]

Thanks for that ,yeah I'm just waiting for the company to come back with a decent quote for the PDM but I think that my free up channels . One of things I wanted to try and do was  push button start/stop but the PDM oil accumulator would fire up first the and then not send the message to start over can until the engine oil pressure was at 2 bar. Is that sort of thing possible. Or would the ecu have to be configured to see the can keyboard, if this is possible  do this and the engine not to start until the oil pressure reach 2 bar. The CAN keyboard is a blink marine type but I've not seen anything like that in any of the pull down CAN menus.

[koracing]

I imagine if you have a pressure sensor input over CAN (analog CAN) you could easily use a GP rpm limit table to allow starting or not - or the stop switch function - to enable injectors and ignition based on whatever parameters and RPM values you wanted.  I usually set an oil pressure failsafe to not allow the engine to run for more than 2 seconds if oil pressure doesn't then go over the values I put into a GP rpm limit table.  There may be other ways to use a PDM to do that as well, but I'm not super familiar with them as I've never personally used one.

[Steve Bull]

I'm a bit of a novice as well when it comes to can systems, trying to tune them. The PDM even though Im just by looking at the software seems quite powerful. It's not as user friendly as the link but its got the same functions, I suppose have got used to the link over the years. Now you can do quite a bit with it but you can't manipulate the data  before you send it onto  CAN. Theres no  extra auxiliary or virtual inputs/output so some of the statements are quite long winded. I'm also not too sure how the timers work how there started or if they reset or just stop. Hopefully wont take too along to get used to it is a bit like trying to tune a car with a Haltech  or motec ecu instead of a link  there's going to be differences some are easier someone more difficult. But I'll have to wait really to see what data gets transfer between the ecu and the PDM and vice versa before I make my mind up how everything is going to work. Things like the gear position sensor that will have to be sent to the ecu then transferred to PDM over Can but I'm not sure how the PDM recognises neutral and reverse,  when you set it up  on the link ecu I think reverse is 11 so it may be something similar to that I don't know.