G3X Isdues

My friend has an SLSA he is renting out. Recently a renter noted the Oil T and CHT going low off scale after takeoff. I gathered the following data today to offer up to the blog brain trust for comment:

I started the engine and observed all normal EIS indications so I warmed up the engine and did some full static RPM runs then reducing the power to idle. I noted that as the RPM dropped the main bus voltage dropped significantly and the CHT indications went into high alarm while the Oil temperature increased, but did not go into hi alarm. Next I slowly increased RPM to achieve a float condition (no charge or discharge on the battery) and observed the CHT and Oil temp decrease. Next I shutdown the engine and then turned on the G3X Touch: The CHT's indicated XX. I shutdown the G3X, waited about 4 minutes and turned it back on to see the CHT's in alarm. I have screenshots if someone wants to send me an email address.



Observations:

1. All indications seem normal for prestart and initial warm up.
2. The temperature indications appear normal when the battery is in a charging condition and high when the battery is discharging
3. The bus voltage is directly related to RPM, as expected.
4. Post shutdown the CHTs indicate invalid initially, but then return to on scale readings.
5. Only CHT and Oil temp appear erratic. Other EIS indications are as expected.
6. Gas tank level varied between 19 and 16 gallons during this data gathering period.

Comment: The CHT and oil temp sensors do not have dedicated ground leads.

Conclusion: The erratic indications appear to be limited to the Oil temp, CHT and Gas Tank level, and there appears to be a correlation to bus voltage/ battery charging state.

Any suggestions, guys?

Could be El Ni?o...

Many times strange behavior is related to a poor ground. Do this test: Measure the milli-voltage between the battery negative terminal and the G3X case with all electrical loads turned on. It should be pretty close to zero.

Thanks for the suggestions. I'll pass them on to my friend to try this weekend. The voltage dropped to 12.7V at an idle of 1620 from 13.2V at 3000 RPM.

alternator or voltage regulator. sounds like you're getting varying voltages at varying rpms.

We did T-shooting today. Resistance to battery negative terminal was about 0.15 ohms at the engine block and 0.25 ohms at the GEA24 enclosure box. The resistance to airframe was 0.2 ohms at the fuel tank. With the master on there was a .27 millivolt difference between the GEA24 enclosure box and the battery terminal. We removed the battery ground lead and sanded the paint away from the battery to airframe connection. It looked OK, and measured OK enforce this, but did not want to miss an easy answer.

The GEA24 mounting plate was primered. That seemed dumb, so we cleaned off the primer with acetone and sanded it before replacement. All the GEA24 plugs were removed and replaced. The ground lines for the CHT, Oil T and fuel level showed 0.25 ohms to battery negative terminal.

We buttoned it all up, and everything worked fine. Seems like an electronic ghost we may have caught by simple regrounding reseating connectors. That's why we used to refer to electronics as working on the principle of "FM". The M stands for magic! Digital relies on "PFM" where P stands for pure.