back to list| Mailing List flyrotary@lancaironline.net Archived Message #46816 |
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Ed and Mike,
Tracy would be the one to comment on this, if he was available, but it is my understanding that both the A and B controllers are running all the time. The A/B switch operates a relay that just changes which controller’s outputs are connected to the rest of the plane. When the injector relay changes contacts there is the possibility for arcing between the contacts depending on whether or not the injectors were turned on at that time. Tracy said once that he had trouble with corruption of the controllers probably due to this arcing and that was the reason for the transient suppression diodes in the injector driver circuitry. Changing to the snubber circuitry, possibly increased the chance for the arcing problem but helped with injector response time. A compromise like everything else. Moving the A/B switch shouldn’t cause a problem unless this has changed the relay response time and caused an arcing problem. I don’t know if the PCM has any circuitry involved with this other than the switch itself. If it does, it’s not obvious. Is there any chance that any of Mike’s injectors are drawing more current than intended? Wiring for saturated when one or more of them is peak and hold or otherwise damaged? That could cause arcing and corruption problems.
How’s that for speculation?
Steve Boese
-----Original Message-----
I think you may be narrowing in on the cause of your problem, Mike.
Remoting the cold start and/or controller selection switch might have unintended effects. IF this were the cause, my bet would be on the controller select switch. I don’t know what all that switch does – but it clearly transfers control of the ignition and injectors to the B controller (when so switched). So several High Power circuits are being turned on (or switched over) to the B controller by a switch that is no longer co-located on the program Controller PCB. Again, IF this remoting of the switches could cause this, the question is HOW?
Not certain of what de-bounce routine Tracy uses – whether software or hardware – but if you turned on the switch to B controller, I would presume the B controller immediately loads the MAP into its working memory. I would assume the Map (as well as other data such as staging) would normally reside in EEPROM and upon activation one of the first things the B controller would do is to load this MAP and data. Now, lets say a second voltage spike from the un-debounced switch were sent to the B controller during the time it was loading the fuel Map, it could cause the chip to do a reset during this interval. That could result in part of the MAP or other data stored in EEPROM getting corrupted. I don’t know the internal coding for moving data from EEPROM to working memory inside the EC2, I do know that for the Serial data its code is in MIDI format.
Using the MIDI format means if only one bit is corrupted out of the 256 bytes used to transmit the Map over the serial link – then all data after that point is corrupted. That is one of the reasons I had to give the Rs232 USART comm. Module in my EFISM chip top priority during interrupts. I can lose any number of injector pulses and it not affect its accuracy enough to display – but corruption of the most significant bit of the High byte MIDI pair during the MAP serial transmission and the remaining bytes are hopelessly corrupted.
I was pretty confident the problem was not caused by the EFISM as it has no way to talk to the B controller, but glad to have it confirmed. The only way I can see the EFISM affecting the B controller is rather round about. You would have to 1st make the change to the A MAP using the EFISM and then use the EC2 to copy the A MAP to the B MAP. Even then you can not change the staging point using the EFISM only the Map and ignition.
A second thought is whether any “ground currents” could be in play. You have probably already done this, but try connecting an alligator clamp (or your favorite attachment device) to the ground of your controller switch and hook the other end to the grounding stud on the EC2. If a ground circuit current/voltage was playing a role this might eliminate it.
Good luck on your trouble shooting. Don’t give up – I think you may be on the right track. Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.dmack.net/mazda/index.html From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mike Wills
So I vented to you guys, lost some sleep last night pondering this, wasted more time today thinking about it, and then went back to the airport to check things out.
I had previously made all of the changes Tracy recommended in case there was an issue with ground or supply noise. I didnt believe that was the problem before, but with no better ideas went ahead and made the changes. I'm now pretty sure that the electrical system is solid.
Another possibility was that there was something about the EFISM installation that caused this problem. Not sure how this could be the case but the EFISM does have the capability to write to the MCT, so maybe something was getting scrambled in the process?
I disconnected the EFISM. And the EFISM was disconnected yesterday when this latest problem occured, so its not the cause. Yesterday just before I quit in disgust I reconnected the EFISM and captured the MCT to make sure it hadnt been corrupted. It looked fine and thats why it was so puzzling.
Today when I started the engine it was clearly still screwed up. I put the EFISM in EC2 monitor mode and immediately saw the problem. This latest problem was due to the fact that my A controller injector staging point had been corrupted and set to 12" MAP. The engine sure wont idle on 4 injectors! I reset the staging point to where it belongs and the engine is back to running as it should.
I now have 5 known episodes of spontaneous changes to the EC2 (possibly more). The first time the staging point was erased and the secondaries wouldnt come on. The next 3 cases (twice in the past couple of days) the B controller lost its program (since I dont have a way to view the B MCT I dont actually know whats happening here, just that the engine immediately dies when I flip to B). And then this last episode with the staging point resetting to 12". I say there may have actually been more cases because my engine has never really ran well on the B controller after doing an A to B copy. But it does run - usually.
So Ed asks is there an action or sequence of actions that may be related? Well the common thread here is switching to B. I ran this engine for about 20 hours of ground testing before I noted the first instance of this occuring. And this coincides with when I started actually flying the airplane - and routinely switching to B as part of my pre takeoff checklist. Then I stopped flying about 4 months ago to make all of these changes and further tune the engine. During this time I dont think I ever switched to B and noted no problems. This past weekend I started prepping to fly and went through my typical pre takeoff prep and once again problems. Started troubleshooting by routinely checking the B controller and once again corrupted the EC2, this time the staging point.
Since my most consistent indicator of a change is corruption of the B MCT its hard to say for sure, but if i can force the staging point screw up a few times by switching to B I'll be convinced. I should note that my install is not standard for the EC2 PCM. I removed the A/B switch, Cold Start switch, and Coil Test switch from the PCM and remoted them to my instrument panel. Tracy noted this as an optional way to do things in my EC2 manual. I dont recall how Tracy implements these switches, but I assume they are SPST to a pullup resistor on the EC2. I dont know if he has any circuitry to de-bounce or noise filter the switch input? I dont even know for sure that this is the cause but seems to be the most reasonable explanation at this point. Stay tuned.
Mike Wills RV-4 N144MW
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