+12V and GND on Motronic

[MonkeyChap]

Folks,

I need to re-map the CANEMS ECU I've got, but don't really have the space (or power, or lights) in the lock-up I keep the car in. So...I'd like to work on it in my office with a bench power supply. From this:

 

 

It seems to be pins 35 and 28, but I thought I'd better ask the experts. Maybe I need 16, 17, 19, 23 grounded too ? Does seem a bit odd to have so many grounds.

Ta

Ian

[Dr Rock]

20 minutes ago, MonkeyChap said:

Does seem a bit odd to have so many grounds.

What is the No.1 thing that goes wrong with car electrics?

[MonkeyChap]

Well, if I had to guess, making the ECU (and its loom) a single point of failure for all the earths ?  

[Dr Rock]

I was thinking earths are the things that cause the most electrical issues on a car. Hope you get it sorted.

[Chris T]

I also have a Canems ECU and although I haven’t played with it recently, I recall you can do all the mapping in the software and then send that to the ECU in the car. All you need is a laptop with a battery once the car is running. I assume like me you got it with a base map the car will run with?

[MonkeyChap]

Thanks, Dr R, Chris. It's a bit frustrating trying to connect up (from a Macbook, using a VM, with USB C ports) in the road outside the house, or in a dark garage 200m from the house...hence trying to do it on my desk. 

[Phill]

I think one ground will be the power ground to the ECU. The others will be the independent grounds for the various sensors. I cannot tell you which I'm afraid.

From the list I would suggest 28 is the ECU ground. The others are marked chassis ground which, like my Megasquirt, all ground the sensors to the chassis. If that makes sense.

[Jonny Hart]

On 3/10/2019 at 8:01 PM, Dr Rock said:

I was thinking earths are the things that cause the most electrical issues on a car. Hope you get it sorted.

Actually, the reason for multiple grounds has to do with all the various externally connected devices.  

As Phill said, sensors often require their own grounds.  Because of the small voltages involved, if a sensor does not have its own short path to ground, it leads to inaccurate voltage readings and false sensor readings.

If you are powering an ECU on the bench you ought to use a current limiting bench supply.  This will protect the ECU in the event that you have it wired incorrectly.   The temptation to use a car battery should be avoided unless you are 100% sure if the connections and at least put a fuse inline.

 

 

[Chris T]

VM ware on my Mac works just fine, I had no problem tweaking things offline and saving the map that was in the ECU or uploading another. Guys at Canems were helpful if you contact them.