Mailing List flyrotary@lancaironline.net Message #9385
From: Ed Anderson <eanderson@carolina.rr.com>
Subject: Re: [FlyRotary] Re: EC2 programming
Date: Fri, 2 Jul 2004 22:18:43 -0400
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sounds like you have the problem identified, John.  It certainly could be the problem.  The Saturation type injectors are generally around 12-16 ohms resistance and the peak and hold around 2-5 ohms.  So the EC2 would provide a nominal 14/14 = 1 amps to the staturation type, but with out the 5 ohm resistor and using peak and hold with lower resistance the current 14/3.5 = 4 amps taking the middle resistance value of the range of each type injector.  With the resistor they should see approx 14/8.5 = 1.5 - 2 amps.
 
The peak and hold tend to open faster than the saturation type so you do not need as much injector-on time to get the same fuel flow.  In fact if the Peak and Hold are driven with an injector pulse duration calculated for a statuation type injector then you would get more fuel flow for the same pulse duration.
 
According to MSD the Satuation types take approx 2 milliseconds to open whereas the Peak and hold only take 1.5 milliseconds.
 
Back of an envelope calcuations shows that With an pulse duration of around 4 milliseonds typical, then  the  2 -1.5 = 0.5 milliseconds difference would equate to a 0.5/4 = 12.5% more fuel flow approximately.  But since your peak and hold were being overdrive with current (without the 5 ohm resistor) the difference may have been even more.  Those suckers probably jumped from closed to full open in 1 msec or less {:>_ with that 4 amp kick.
 
That is one thing about these Mazda Rx-7 injectors, its really easy to get caught if you don't actually measure the resistance.  I have satuation type injectors with the same color electrical connector AND same part number stamped on the electrical connector but one set are peak and hold and the other 4 are saturation type.  Error in manufacturing?? don't know.  Also, the 560 cc saturation injectors came with a purple connector and an unpainted (silver) body.  Guess, what, some folks have cleaned off the scratched up black paint off the 460 cc injectors and with a faded red connector - it can (and has been) mistaken for the 560 cc injector.  So you gotta be careful.
 
Ed
  
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
From: John Slade
Sent: Friday, July 02, 2004 9:24 PM
Subject: [FlyRotary] Re: EC2 programming

I think I found the problem.... or at least Tracy did. He realized that my symptoms would be a lot like what you'd get if you used peak & hold resistors without the 5 ohm resistors. 
 
About 2 years ago I got 2 purple 550cc injectors from Bruce. They were Saturation type, so I didn't need resistors.
A year later I got two more from the local Mazda shop for the secondaries. They were purple, so I ASSumed they were the same. I tested them tonight and found that they're the peak & hold type. Without resistors they get too much current and they don't open and close as the EC2 expects. Result - uncontrollable mixture problems.
 
OK, so how do I get 2 * 5 ohm 25 watt resistors on a holiday Saturday?
 
John (mix & match) Slade
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