ADS-B problem

[procharger]

After flying with it I now have some kind of grimlin, during 3 flights all of a sudden

my CHT and oil temps jump to 350 -400 degrees, done this 3 times, today I landed

and stopped engine, while sitting, temps climbed even higher, turned off battery

3 seconds later I turned it back on and readings were normal, I then removed panel

unplugged ADSB and flew again for hour with no issues, what the hell?

[Anticept]

Grounds.

Make sure they are pristine. CHT, Oil, and EGT are all sensitive to floating voltages in a EMS 120 (if that's what you have).

A GDL-82 doesn't use much power though, so I am curious myself. Still. Those grounds need to be CLEAN!

If I recall, you have a CTSW. Put a voltmeter lead on one of the grounds on the post in the upper right corner inside on the firewall, and the other at the battery negative. Turn EVERYTHING on (but engine stays off).

If you see more than a couple tens of milivolts, your ground isn't good enough. The lower, the better. Dynon recommends no higher than 5 miliamps but that's really hard to do and would require tearing out the whole grounding system to replace with larger gauge wire.

[procharger]

Are you saying because of the ADSB I might need to redo grounds?

[Anticept]

I'm saying check them. That should be the first thing you address.

Secondly, where is the ground for the GDL-82 run? Does it go all the way to the grounding bolt, or did it get pigtailed somewhere else (bad)?

[procharger]

Looks like is grounded where all the other grounds are inside fire wall.

[Anticept]

Alright. Check voltage drop as aforementioned. Make sure everything is running.

Check voltage drop from the engine too.

[Cody85]

2007 CTSW.      I have the same problem.  CHT, OIL Temp, and even sometimes oil pressure gauge are getting some type of electrical interference causing them to wander about.   I've found that when I turn on landing light or interior lights, the gauges will temporarily correct to true,  then slowly wander again.   Mechanic always tightens wires but problem seems to persist.   Any suggestions?

[WmInce]

First thing I would do is . . . thoroughly check all ground points.

[Runtoeat]

Wondering if the ignition switch contacts might be involved?  Maybe some bleed-thru of voltage into ground circuit?  Or, maybe some fluctuating voltage being supplied to the instruments?  After many hundreds of cycles, the switch can start acting flaky.   

[sandpiper]

On 7/28/2018 at 4:44 PM, Cody85 said:

2007 CTSW.      I have the same problem.  CHT, OIL Temp, and even sometimes oil pressure gauge are getting some type of electrical interference causing them to wander about.   I've found that when I turn on landing light or interior lights, the gauges will temporarily correct to true,  then slowly wander again.   Mechanic always tightens wires but problem seems to persist.   Any suggestions?

I don't think just tightening grounds is the answer. You need to take them apart and scotchbrite (scuff) all the connections - even if they look clean.

[procharger]

After cleaning every ground you can get to, it may fix the problem, it fixed mine.

I don't understand why these planes are picky about grounds??

[Anticept]

Because the wiring design is the worst part. A lot of hodgepodge half dones.

There are wires using the shielding as a ground. While acceptable (barely), it's not preferred. Shielding is meant to be used as shielding, not as a current carrying conductor. And it doesn't have the mechanical flexibility of copper.

The grounding design should have used a terminal block (pre LS) or ran a heavy ground to the terminal block and bonded to both strips (LS+) rather than used a bolt, which corrodes.