The datasheet for the map sensor shows a 470pf capacitor between the output and ground.  The 0.1uf capacitor may be slowing the response of the sensor too much.

Steve Boese

> On Jan 14, 2020, at 9:23 PM, Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net> wrote:
>
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>
> A frustrating few hours
>
> I got down to the hanger this morning to look into the EMI in both the engine controller and EFIS.
>
> First thing I did was reroute the radio coax so that instead of being in close proximity to many cables down the centre of the aeroplane instead down the very right hand side.
> This increased the distance to various wire looms by ~450mm.
>
> Prior to this change the symptom outside the hangar was from memory about a 300ft/min vertical speed on tx in the Skyview EFIS.
>
> First test with radio tx after the reroute of coax inside the hangar yielded a "4 times worse" symptom in the EFIS! ~1300ft/min reading on tx.
>
> I then tried the test outside and away from the metal hangar by 10m and the symptom was reduced to ~600ft/min and increase in symptoms of about 100% on original problem.
> I then applied a clamp on ferrite to the cable loom entering the ADHARS unit from where the symptom originates.
> On tx outside the hangar again the symptoms are far reduced by over 1/2.
>
> So if I had left the radio coax where it was, the ferrite may have fixed the problem in the EFIS.
> I have more ferrites on order and they appear to be very effective, so will use these to attenuate the RF entering the various pieces of equipment.
> EMI trouble shooting is indeed a black art!!
>
> I also removed the Engine Control unit and soldered 0.1uF ceramics across the outputs to earth of the MAP sensors of both A and B computers as specified by Tracy.
> On reinstalling the Engine Control unit I was not able to start the engine!
> It would fire but not run on either controller.
> So spark and fuel are present, but not to remain running.
>
> So the mod appears to have messed up the MAP sensing.
> My initial thought was that the caps were actually resistors packaged wrongly but they measure open circuit.
>
> So the few hours of mods and testing has been exceedingly frustrating, going backwards at every turn except for the 1 ferrite showing itself to be very effective.
>
> I’m hoping my next outing will be very much more fruitful.
> In the mean time I’ll ponder what could possibly cause both Computers in the Engine Controller to be u/s.
> If I cannot discover my deliberate mistake. I’ll remove the caps and retest the Controller on Friday.
>
> Cheers
>
> Steve
>
>
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