bartrim(at)gmail.com
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 Posted: Tue Nov 05, 2019 1:05 am Post subject: Engine monitor display scramble from EFI sense line EM2 from |
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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
[img]cid:ii_k2lkj5gk0[/img]
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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