The previous owner of my Trinidad installed a JPI 930 primary engine monitor on the right side, removing all the old indicating instruments on that side, except for manifold pressure and rpm.
However, he left the central upper part, the vertical linear indicators, with oil pressure, temperature and voltmeter.
As I am preparing to install the new L3 Lynx NGT-9000 transponder in the middle, I wonder if I can simply remove those indicators as well, in order to make room for the new unit.
I think with the JPI 930 being primary, I can do that, as I already have all these on the engine monitor display. But I may be wrong… Any input on this would be appreciated.
Quite simple paperworks, look into the documentation of this EDM 930 installation and the release to service certificate. It should say what has to stay and what not.
I would look at this in detail.
Years ago, following multiple failures of the oil pressure indicator, I installed a backup instrument. This had to use a separate transducer because (a) you cannot share a bridge transducer among two indicators (short of doing some significant electronics, with “interesting legal issues”) and (b) it was the transducer itself which kept packing up. The point is that if you install a second oil pressure instrument you have to install a second transducer which is dedicated to it. But sometimes installers do a bodge; for example I know one TB20 which has two fuel flow instruments driven from a single flow transducer, which works until one of the two instruments is powered down and then they both go dead… If you remove the old display, the new one might be affected…
And same goes for temperature.
The voltmeter will be OK to remove anyway.
So check the exact wiring. The work pack is your property, and should contain the wiring.
If the 930 is certified as PRIMARY for all its functions, and the installation doesn’t have any restrictions, it is ok to remove the old instruments. Not always wise though… in GA the indicating systems fail more often than the things they are monitoring 
These devices look great but they are fragile by design.
If you short the cable on one gauge in the EDM930, this will bring down the whole interface board and fail several other gauges.
This happened to me when a cable (provided by the manufacturer) had a short due to poor connector soldering.
Makes one wonder how this got through certification…
So I definitely recommend avoiding putting all eggs in one basket.
The ideal engine monitor is a simple data logger with several instruments feeding it.
There is no benefit in having your fuel management and your electrical system monitoring on the same display, same CPU etc…
Even the “smart” alerts are anything but smart.
Your oil is too cold, your coolant is too cold and oil pressure too high – right after startup, so you now have the additional task of acknowledging the alerts.
Then it distracts you during final because it decides EGT differences are too great… at idle… you get the idea.
Several thoughts:
Unless you are required to manually manage the throttle setting of a turbocharged engine (no automatically controlled wastegate), how wrong could you get the throttle setting? For a normally aspirated engine, it’s impossible to overboost it, so as long as you’re not running dramatically oversquare, will there be a real problem completing a flight following the failure of a MP gauge? Similarly, without a tach, can you manage the prop control? Yes. If the engine is screaming, you’re going to reduce RPM, and maybe throttle too, you can do that by ear. As the failure would be following takeoff, there’s less chance that you need to select full power with precision. I would quite happily continue flight with MP and tach inop, without worrying about setting the power too far off, unless it was a manually set turbo’d engine, then yes, you really should have an MP. SO, for me, the EDM 930 is good enough, and reliable enough for me to surrender the original engine instruments.
I installed an EDM 930 in a C182 as the primary replacement for all of the engine instruments. Generally I was very happy. One big gotcha with that was an error in the fuel quantity indication. The instrument was not capable of a logical self check. The two quantity indicators displayed much more fuel than was aboard – as much as a 30% error. I was able to convince JBI of the problem when I proved that the sum of the fuel available, and fuel used, dramatically exceeded the fuel quantity of the aircraft. I ended up disregarding the qty, and simply when by fuel flow vs time, that was very precise.
The EDM 930 in your plane should be serialized to your particular airplane. That should include the programming of all of the range markings, which is a part of it’s STC for installation. The engine limitations are Type Certificate Data Sheet limitations, and therefore are required to be conveyed by range and limitation markings (green arcs, and red lines). This came up for me as EASA required an RPM reduction on this airplane for noise compliance (I actually had flown the EASA noise test on it). That created the need for changed range markings on the EDM 930, but JPI told me that they would not do it, as the unit was STC’d for the plane with different (faster RPM) limitations than I needed. I was informally brought to understand (by an entity nor JPI) how to enter the programming pages, so I went to the plane, changed the marking, and test flew to show that there were now correct. I then emailed photos to EASA, who accepted my work on this.
Once you determine the approval status of the EDM 930 to replace your primary engine instruments, changing limitation markings may be your next task. The 182 is EASA STC’d with the EDM 930 as primary for all engine and fuel indicators, so it’s not a stretch to similarly approve a TB-20 if EASA is receptive (they were with me).
