MPGuino install on 2002 BMW R1150RS - Fuel Economy, Hypermiling, EcoModding News and Forum

jsibre · 05-05-2014, 12:38 AM

Hi,
The title is a bit misleading because this post is less about the install, and more about the problems I'm having.

Sorry in advance about the goofy links in the text - I haven't made enough posts to be allowed to include links.

First, a bit of history - original post: h ttp://ecomodder.com/forum/showthread.php/official-mpguino-preassembled-now-available-6914-33.html. I bought my MPGuino (from DCB, via donation) to install on a motorcycle. About 2 1/2 to 3 years ago. I bought an Arduino Uno and display at the same time, just because I like to tinker, and thought maybe I'd enjoy Arduinoing.

My bike doesn't have a VSS - has a mechanical speedo/odo. I messed with Hall Effect Sensors a bit (to provide a VSS), and then got distracted, and then moved to a new house. Since moving, I haven't messed with it until the last few weeks. I rigged up a reed switch for a VSS. Wired everything up, and got it kinda working, but I was getting some crazy speed indications. And they weren't from the reed switch (I promise). I disconnected it. Even with no VSS hooked up, I got crazy speed indications on the MPGuino.

I bought an o-scope. I'd wanted one forever, and this looked to be a problem that I wouldn't fix without one. I noticed major flyback from the fuel injectors (~80v, which appeared to be clamped at that voltage by...something in the ECU maybe?), and spent about a week trying to eliminate it from the MPGuino's world without keeping the injectors open. Simply adding a flyback diode across the injector would keep it open noticeably longer. Adding a resistor in series helped, but it was dicey finding a value low enough to do some good, but high enough to not keep the injector open significantly longer. I finally added an opto-isolator to sidestep the problem.

That worked, but then I noticed that the speed indication was still acting crazy!

I tried adding some power supply filtering to the 12v input to the MPGuino. A pi filter, IIRC it was a pair of 150uF caps and a 10mH inductor, but I'm not sure. Anyway, it didn't help.

Mind you, the VSS had been long since disconnected. I could see that the timing of the noise that was triggering the erratic speed indications was related to the injector pulses, but the magnitude was somewhat random - nothing huge, a volt or two or higher. I don't think it was getting higher than the supply voltage, but maybe it got a bit higher. Nothing like the flyback from the injectors though. The noise was very short duration (I haven't measured it, but it makes the injector pulses look very fat in comparison.)

I'd concluded (with no proof) that the MPGuino was producing the noise in response to the injector pulses. I set it aside for a week.

Fast-forward to today:----------------------
I built up a second MPGuino on a breadboard from the Arduino Uno, the display, and a couple zeners and resistors. Hooked it up to the bike and it worked great! That's without even messing with the opto-isolator. It was running v0.75 of the code (the last version that you could load in via a bootloader on an Arduino, vs an ISP programmer, which I don't have - yet.)

I concluded that there must be something wrong with my pre-built MPGuino, so I opened it up (I'd built a nice little gonna-be-water-tight enclosure for it) and inspected it for bad solder joints, etc. I saw that one lead on the power supply cap was not soldered. I mean, it had a dab, but the lead was loose in the plated thru hole. I resoldered it, and resoldered a lot of other functional but not-so-great joints.

I tried hooking it up again. Same problem. Crap.

So, I started comparing the components on the board to what's called out in the schematics here at h ttp://code.google.com/p/opengauge/source/browse/trunk/mpguino/, and found that the capacitor I mentioned above was a 470uF when the schematic called for a 330. I don't see that doing anything but good... However, R1, 80 ohms on the schematic, is a 453 ohm on mine! I thought that might be the problem, but on further research, I found h ttp://ecomodder.com/forum/showthread.php/official-mpguino-preassembled-now-available-6914-29.html#post243874. Hmmm...

So, I'm ready to build mine from the Arduino, and solder it all up. But the MPGuino is still nagging me. I didn't see any other wrong/misinstalled components. Maybe something damaged? Has anyone else seen problems like this? Any ideas?

Thanks,
Jason