Al,

 

What I don't understand is why am I just now having this problem.  I've been flying for 11 hours and this problem just recently surfaced.  The only change I remember doing recently was replacing the electro-mechanical injector staging relay with a solid state relay.  Tracy has recommended that I add a second diode from the second output terminal of the SSR to ground. 

 

I will try that, but I will try to reproduce the failure (on the ground) by triggering the radio, and also turning the transponder from off to standby to on.  The transponder is the closest piece of electronic gear to the EC-2.  As I understand it, the transponder also puts out much more wattage than the nav/com.  

 

One more possibility is that the tach lead coming from the EC-2 is unterminated.  I have since learned that it is bad practice to leave wires unterminated.  So, I will remedy that this weekend too.   

 

Also, I would like to know where the best place would be to connect a scope lead on the EC-2 to look for noise.  That seems like the easiest way to track down this problem.  I will ask Tracy for suggestions before proceeding with the scope. 

 

Mark S.

 

On 12/17/07, Al Gietzen <ALVentures@cox.net> wrote:

  I have separated the injector wires and the coil wires from the rest. There's a ground block located between the two with a connection through the firewall to another ground block and engine ground.  Batteries are in the back though.  There's a #2 welding cable going from the ground block to the battery.  It routes down the right side away from all the smaller wires. 

When you say "smaller wires" do you mean current carrying wires that power things, and return current from the alternator – or just instrumentation wires?  Good practice, especially in a composite plane, is to use twisted pair (power/grnd) to cancel noise. Having power leads away from the ground return forms a big loop antenna for radiating EMF from wires that carry noisy current. I suspect that is not much help at this point.

 

Probably the noisiest wires we have in our planes are the alternator output and the power for the coils and injectors.

 

The nav/com is mounted near the EM-2 and could possibly be the culprit, based on Al's recommendations.  The EM-2 display is right above the nav/com.  Maybe I need to move the nav/com to the back of the plane? 

 

The Nav/Com itself should not be an issue, the antenna lead should only 'leak' low levels of RF unless the impedance match isn't good, or bad connection to the antenna.  Is your EM2 display remote from the Data Acquisition Module?  Those leads, the serial leads between the EM2 and EC2, and the power leads to the EC2 should be kept away from the noisy wires.

But then, I'm no expert on this stuff.  Tracking down electrical noise takes an expert with an oscilloscope.

You were on a good track suspecting the solid state relay if the problem did not occur prior to installing it. You may need to add snubbers there.  Switching relays definitely generates a noise spike.

Al