Need help with eletric stuff - 1989 M20J MSE

[Tércio Rodrigues]

Guys!

 

Need your help again with some issues on my 1989 M20J MSE. Few months ago I had a major electrical failure (you can read here), and now, after lots of avionics repair, we're getting things as they were before, little by little. But still got some annoying troubles:

 

- We had our R1 Eletronics International Tach replaced by a new one, but now we have approx. 30-60 RPM error, for example, at T/O, full power, full high RPM, the tach displays 2730-2740, and once the plane starts rolling, it may rise to 2760. We have no reasons to believe that the prop its really at more than 2700 since with the old R1 it never excedded it, and any adjustment was made at the governor, and we had checked rotational speed with a Tuning Fork (is this the right english term to reffer to it?) and it indicated 2700, full power, full rpm. We had not replaced the mag sensors, though, we are using the old ones. Do you think this could be the problem? 

 

- We replaced our Gauge Cluster, but sometimes, when you push PTT (both sides), the oil pressure indication drop till yellow arc. This happens on both radios (GNS430 and KX155), on transmitting modes. It seems to happen with frequencies higher than 130,00 MHz, but I'm not sure of this and if it has anything to do with it.

 

- Our EGT/OAT (B & D P/N 0230-003, Mooney P/N  880001-509) is out of work: I know it gets energized, because it is noticeable when I pull the CB, but it just give wrong indications such as -30°C when the real OAT its like 30°C, and no rise in EGT at all while leaning.

 

- Finally, the interior lights seem to be flashing at very high frequency, slower when the engine is at slower speeds, and higher, when the engine is at higher speeds. During flight its almost imperceptible, but during taxi its quite clear.

 

Some general info: its a 28V system, SN 24-3139. We have replaced the Voltage Regulator and tested it several times in the plane (direct in the VR and with a multimeter through the cig lighter) and it seems pretty steady on the correct range. And at last, but not least, I am (as does the plane) in Brazil, so all of these nice avionics shops you guys indicates here at Mooneyspace are sadly unavailable for me!

So, any help will be much appreciated!!!

 

Tércio

[carusoam]

Tércio,

Sorry to hear that you have continuing challenges.

One piece of information I might be able to help with. There are apps that can discern rpm based on sounds from the engine. Any smart phone can do this. The Apple AppStore has a few as well...

Test the rpms at lower settings first. There are limitations on how long (time) and how high the rpm is allowed to exceed the red line.

The push to talk switch may be mis wired...? Sounds like it is opening a circuit to ground. It should not be connected to any other instruments...

I am not very familiar with the J. From my C experience... My IP had a single ground that many wires that ran to a single point on the steel frame behind the IP. It may be a good time to review where the grounds of this equipment are attached, or not...

So many things not working correctly seems like a big grounding problem, a loose connection of several ground wires?

Are you able to troubleshoot electronic connections and wiring?

Start by reviewing the newest equipment installed...

Keep in mind I am not a mechanic, just a PP.

Best regards,

-a-

[N201MKTurbo]

It sounds like your engine grounding strap may have problems. Just check to make sure it is ok.

[cliffy]

Ditto to N201  reply  Make sure your battery ground strap and your engine to airframe ground strap are both tight and clean of all corrosion at both ends of each one. Check all the connections on the alternator also.

The EGT may be bad temp probe at the exhaust stack.  

Wiring issues can be very trying to fix. You might also try tripping and resetting all circuit breakers just to make sure they are all have clean contacts and seated good. 

[gjensen]

Be careful, in my prior plane, a piper Dakota with the single dual mag, poor grounding was the cause for total mag failure and a subsequent force landing into a pnut field. The mag was repaired and ten hours later it failed again and we made KSSI. Investigations determined poor grounding after a new engine install was causing the points to over heat and burn up over time. Needless to say, I sold that plane and am now a happy owner of a mooney with two independent mags! So with all the grounding issues you appear to be having keep a close eye on your EGT's and if they start to rise, get on the ground quickly.

[N601RX]

The EI tach doesn't use a sensor, it just picks up the signal off the p-lead of the mag through a resistor. It comes with different value resistors and you may have to try different ones to get it to read correctly. Other tachs like JPI uses a Hall effect switch and senses the North and South Pole transitions of the magnet inside the mag. Because the ei is directly connected to the mag it is more prone to pick up noise if there is any present.

[Tércio Rodrigues]

carusoam, N201MK, cliffy, gjensen and N601,

 

Thanks a lot for all the advices.

 

I have an update: our GNS430, which was damaged in the electrical failure, and revised in the US by Garmin, just went out again. It might be just a screen problem, but it may be another font damage font due to a short, and I'm starting to think that I have at least 3 events related to it (2 times damage on the equipment itself, and the PTT - oil pressure issue, just on transmitting modes). I'm going to start checking the instalation looking for shorts, as well as for grounding problems. It would be weird, because it was installed at least 10 years ago, but it's actually the newest equipment installed.

 

Thanks again for the help!

 

Tércio

[philiplane]

flashing interior lights point to a failed diode in the alternator. This is very bad for avionics.