JPI EDM 900 - MAP fluctuations

[IvanP]

Hello All,

I have been experiencing a rather strange phenomenon with JPI EDM 900. The monitor is installed in 1990 Mooney Bravo that I purchased few months ago. Whenever I transmit from either radio (GTN 750 or KX 165), the MAP indication on the EDM 900 spikes (no changes in the throttle settings and no changes are seen on the ship's mechanical manifold pressure indicator). No other indications of the EDM 900 appear to be affected by radio transmissions and it happens regardless of whether the engine is running or not. The magnitude of the fluctuations appears to be affected by frequency (some frequencies produce higher spikes), but I was unable to determine any specific pattern. 

I checked the usual suspect with EDM gremlins - grounding. The unit is grounded directly to the engine block as directed by the installation manual. I pulled all the data from the monitor and it appears that this phenomenon has been present for couple of years but apparently went unnoticed by the previous owner. I will try calling JPI but do not hold much hope, given the rather lackluster responses to prior technical inquiries. 

Thank you in advance for any advice or thoughts on how to eliminate this behavior.

Regards,

Ivan 

[EricJ]

If the MAP signal wire is shielded, check that the shield is securely grounded.

[IvanP]

MAP connection is not shielded in this install, nor is it suggested in the JPI installation manual. I was thinking about adding shielding to the MAP connection, but it appears to be a rather difficult task in this install. Give the uncertainty of results, I am hesitant to rip into it.

[EricJ]

3 minutes ago, IvanP said:

MAP connection is not shielded in this install, nor is it suggested in the JPI installation manual. I was thinking about adding shielding to the MAP connection, but it appears to be a rather difficult task in this install. Give the uncertainty of results, I am hesitant to rip into it.

If it's not normally shielded I wouldn't add it, as that may not be where it's getting in, anyway.    I think you're right to look at the grounds, including the other shield grounds, backshell, display, sensor, etc.