Mailing List flyrotary@lancaironline.net Message #65309
From: Todd Bartrim bartrim@gmail.com <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: EM2 display scrambling
Date: Wed, 6 Nov 2019 00:00:39 -0800
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Thanks for all the comments. 
As far as grounding. I always pay very careful attention to grounding and am fairly confident that it is done properly, but I'm always still open to the possibility that I've overlooked something. In industrial instrumentation, it is a high noise environment so cable shields are standard and we always use the mantra of "No Shield in the Field". Now the wire in question actually has the shield grounded at the EM2 rather than the EC2, simply because the EC2 wiring harness came first and the EM2 was added later. This really should have no effect and the cable is only about 18" long.

   And yes, my plane has first flown long ago, but never really finished, but yes this problem has existed since I first got the EM2, which was probably about 2 years after my first flight. But it used to be much less frequent, so was little more than an annoyance. Then as I didn't fly for 12 years, I really didn't think about it.

However.... The mention of cold solder joints may be the problem due to another discovery that I coincidentally made, but didn't think was related until reading these responses.
On Sunday while I was investigating the wiring, I had the back-shells off of the DB37 connector on the EC2, taking a close look at where the EFI sense line was spliced into the #1 primary injector wire and in doing so I was tweaking a few of the other wires as I separated them for inspection. The engine was idling smoothly at this time, but it suddenly stopped. I restarted it with no issue but then went to the wires I'd been touching before and this time it stumbled when I pushed one way, then caught again but as I pushed again It stopped dead again. This time there was no restart, and I could see on my wide-band O2 monitor that it was full lean (display says "AIR"). This made me suspect the crank angle sensor wires were at fault as the EC2 was not seeing the engine rotate so was not sending fuel or ignition pulses. Another few tweaks of those wires and the engine started and ran fine again. I quickly was able to determine that it was the wire on pin #4 which is to the crank angle sensor (CAS). So expecting a broken wire at the pin solder joint I checked it thoroughly and found it to be fine. So now I expected it to be the DB37 connector on the board, but right then I could do nothing about it, so to investigate further I reassembled the connector back-shell and reconnected the harness and fired up the engine. In this state, it seemed pretty secure and pushing/pulling gently on the connector could do no more than an occasional miss. But a familiar occasional miss. At a high power setting (tied down, wheels blocked), tweak the wires and just the slightest occasional miss of the engine was exactly the little Gremlin that I'd experienced ever since my first flight. But it was so seldom and I'd always figured it was tuning or something as originally the EM2 didn't have auto-tune and I didn't have a wide-band O2 sensor. With these new tools, the engine is tuned very well, but I just figured maybe I was missing a spot.
   Anyways, I took the EC2 circuit board home with me and under a large magnifying glass I found that pin #4 had a failed solder joint that was easy to see. Just to confirm, I used a DMM clipped to a spare D-sub female pin onto pin #4 and confirmed it was intermittently open. A simple quick touch with the soldering iron fixed the problem. 
   Now while I'm grateful to have found this problem as this is flight critical, I also had dismissed it as it was not the suspected culprit wire. However possibly it was creating the noise that the EFI line is picking up. Tracy even warns in his install manual to pay particular attention to shielding the CAS wires and routing the away from other wires as they are particularly noisy. Unfortunately inside the crowded confines of the DB37 connector back-shell it is difficult to achieve this. Add in the broken solder joint and it is a recipe for noise. 
It seems that it may be prudent to touch each of the pin solder joints to re-solder all of them. I only have the EC2 circuit board with me at home, but if the problem persists, I will bring home the EM2 board for the same treatment.
  I'll also try installing a simple low pass RC filter as well. And if that doesn't work I'll use a scope to record a waveform for analysis
Thanks again for your comments

Todd Bartrim


On Tue, Nov 5, 2019 at 11:25 AM Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:
Try searching this list for subject containing "EM-2".

Several earlier postings on similar subject.

Fairly sure it boils down to grounding issue or need for filtering.

" 2. Starting at about 6000 RPM, the RPM display on the EM-2 starts dropping out.  By the time the RPM gets to 6500 or so it is almost completely gone, but comes back when I reduce the throttle.  I have an optical prop tach so I know it's speed"

Tracy: "For the RPM problem, try a  5000 - 6000 (not critical) ohm resistor in series with the injector connection to the EM2 and then connect a capacitor of about .01uF.  from the P3-6 connection to ground."

Finn

On 11/5/2019 4:12 AM, Todd Bartrim bartrim@gmail.com wrote:
Below is an email that I just sent to the AeroElectric list, but as many of you on this list also use the EM2 but may not be on that list, I thought I would send it along here too.
Charlie, I know you are on both lists, and are a frequent contributor on the AE list, I figure your insight to the EM2 could be invaluable along with anything Electric Bob can add.
But I welcome any advice from anyone who may have also encountered this issue. I have sent an email to Tracy, but as he seems to be offline up in Colorado, I'm hoping to be able to solve it without bothering him too much.

Thanks, Todd

I have an issue with my engine monitor display where the display will scramble leaving me with a meaningless display as can be seen in the attached picture
EM2 display_scrambled.jpg
The engine Monitor is from Real World Solutions and is the very early first edition EM2 (serial #003). I also have an early edition EC2 (engine ignition and injection controller).
RWS was Tracy Crooks company before he retired, and he still provides some support when he can, however he also is enjoying his retirement offline so is often hard to get a hold of, 
so I thought I would pose the question here while awaiting a response so maybe I won't even have to bother him.

  So here are the details of the problem. The engine monitor has 36? different parameters that it displays on 8 screens. There are 24 different sensors (pressure, temperature, level) with the remaining being provided through a serial data link from the EC2 along with an EFI sense which is connected to the #1 primary injector output from the EC2. I've determined that it's this last wire that is causing my grief. 
This EFI sense is measured for it's pulse width in order to calculate a surprisingly accurate fuel flow, RPM, HP, fuel remaining, MPG (for efficiency). But the noise on this line seems to be the cause of the data scrambling on the display. Simply pressing the cancel button (there are 4 user buttons to control display) will rest and clear the issue. 
   But here's the weird part. It seems to be related to relative humidity. During hot dry, summer weather this display will rarely scramble, sometimes going up to an hour without an issue. But on cooler humid days I would have to reset it every few minutes which gets a little annoying. However right now as we are not enjoying the cold November rains before winter will arrive with cold dry weather, I'm finding that it is scrambling almost immediately after a reset. This makes no sense to me, but I've observed this pattern enough to be sort of certain that it is not a coincidence... but I could be wrong.
In any event, it matters not whether it is or isn't triggered more by the humidity, but what it did allow me to do is determine where the issue is coming from as before it was too random to allow easy troubleshooting but now as it is more consistent it was quite quick to narrow it down.
  I've cut this line (which is shielded with only one end of the shield grounded) and installed a connector. With it disconnected, the EM2 display is rock steady (up to a 10 minute ground run) but with no RPM or any fuel, power, or efficiency data. Connect the line and it immediately will scramble. I estimate that the frequency of the injector pulse on this line would only be at max about 100Hz at 6000 RPM. I've considered that a simple low pass RF filter to ground may work as the frequency that I'm trying to measure is well below what the filter would remove, but would it still have an effect on the pulse width? which would be undesirable as that would effect the signal driving the #1 primary injector. 
  I'm hoping that someone can suggest an easy fix so that I can implement it when I get back up to the airport this weekend, other wise if more data is needed to help find a solution I will take a scope up there and try to get some more detailed data.
 Right now our days are getting pretty short up north here so it's dark by the time I get off work, so I'm restricted to weekends only. Thanks for any help that can be provided.

Todd Bartrim

RV9 13Bturbo


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