ECU to PC communication problem with UTC

[Eho]

Hi,

We are using Motec M880 and ADL dash logger on our Yamaha R6 powered Formula SAE race car. We are very familiar with ADL but have just made a initial startup with M880. Everything went very well and without even a single problem until now. We had already made quite a lot tuning on a superflow engine dyno when suddenly communication between ECU and PC got unstable. Engine idles and revs nice but immediately when you get on full load-> ECU Manager freezes-> starts to read ECU data-> again freezes-> starts to read ECU data-> etc. When you decrease the load/TPS everything works fine again. Engine works fine all the time. Strange thing about everything is that the setup might work fine for couple of days but suddenly can't get stable communication at all. Also strange is that communication between ECU & ADL is never interfered.

Our current setup is M880 with M&W CDI, ADL dash and UTC adapter. ECU is fitted to superflow frame and connected to ADL&UTC outside the dyno room with 2m long twisted pair CAN. CAN has a 100ohm resistor at both ends (UTC also has a internal 100ohm resistor).

I have tried almost everything but problem stays. All the wirings has been done properly, all the communication wires have been checked & done by following the motec manual, CDI & other interference has been excluded, ground points separated & checked, several resistor setting tested on the CAN, removed the ADL, changed the PC, re-installed the softwares & drivers, changed the UTC & USB wire.

First I thought it would be some external interference but while scoping the CAN traffic I noticed that UTC makes quite a lot noise to the signal?? I'll attach some lousy pictures but hope they make the point:

ECU can

ECUcan (Small).jpg (30.15 KiB) Viewed 13541 times

ECU can with UTC connected(connecting PC doesn't make any difference)

UTCconnected (Small).jpg (32.5 KiB) Viewed 13540 times

Noise created by the UTC

UTCnoise (Small).jpg (34.08 KiB) Viewed 13543 times

I'll be re-posting if something unmentioned comes to my mind.

Thanks,
Lauri Eho

[MarkMc]

Hi Laurie,
Interesting problem. Can you tell me if you have channels going from the ADL back to the ECU?

It still sounds like a problem due to interferance simply because it happens at high load, i.e. when the ignition system is doing its most.

How have you got your earths setup? I assume you have the ADL on the same power supply as the engine itself?

I always make sure all of my earths on a vehicle are at exactly the same point for everything, normally at the point where the battery negative cable connects to the chassis.

How have you checked your earth points? Based on a voltage drop back to the battery negative or just a resistance value from the device back to the battery negative?

Long USB cables to the UTC are not good either, I believe the 1-1.5m ones are the best bet.

Scoping my UTC and CAN cable here they are definitely not the cleanest wave forms I have ever seen, probably why they have two signals for noise rejection.

Like I said if it only happens when there is a lot of load on the engine, i.e. the ignition system, I would say that is where your problem lies.

[Mazi]

CAN Bus is very immune to different noises as far as they are not differential. Try to add and invert scope channels and you will see what the bus receivers are seeing too. I think that half of your noises will disappear.

The easiest way to find out if something is wrong with CAN bus signals, is to check if ACK bit is present on the end of data string. It is usually different signal level because is sent from another CAN node. If the last signal has different level but is wider then the shortest signal in the frame you have an error or overload flag present on the bus. Sometimes it helps if 120 ohm terminator is replaced with two 60 (56) ohms resistors serial connected and with 100 nF condenser connected in the middle of them with other side on the ground.

Do not forget. UTC is powered from PC via USB and not from ECU's 8V. Typically an unpowered CAN node will not disturb bus until VSS (GND) is connected.

[Eho]

Hi,

I'm deeply sorry for this late reply but we've been in quite a rush for whole winter. Thanks to Mark and Mazi for your help, I checked all your advices back in December but everything was ok.

About the noise on the CAN, we managed to locate the noise source (UTCnoise.jpg from my previous post) to the computers USB port. When we connected the computers USB ports ground(-) to the Motec UTC the noise was immediately there. It also seemed that the noise on the USB came from the battery charger of the computer.

We started to tune the engine with computer not connected to the charger and the connection problem seemes to be vanished!? All in all I'm still not sure what caused the problem. Our dyno room is in automotive emission research laboratory with lots of noise so the problem might as well be caused by it but if someone has samekind of problems I would advise to try disengageing the battery charger.

[MarkMc]

Thanks for the update Eho. Strangely enough we like getting feedback when a problem is sorted.....most of the time people take the advice and run and you can only assume that it was fixed when you never hear from them again.