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1st Engine Start Issues - Garmin G3X

ntolman

I'm New Here
I had the chance a few days ago to start my engine for the first time. Everything started up fine but I did notice a few issues that I need some help figuring out how to fix. I am building ELSA with Garmin G3X.

1. Oil temperature showed a gradually increase, but then all of a sudden dropped off (meaning gauge showed big red X). It came back up for a second, but then dropped again.) The 2nd and 3rd time I started the engine the oil temperature gauge seemed to drop off even sooner.

2. The CHT2 has a big red X. Ended up taking the CHT1 wire and hooking to CHT2 sensor and the sensor was fine. I tested the CHT2 wire continuity to the Firewall Forward pin and it was fine to that point. I am not sure where it goes from there or how to narrow the problem down.

3. The fuel PSI seemed to fluctuate during the 1st three starts of the engine. It would show fine in the range of 5 to 5.5 or so, then it would drop below 2 for a couple seconds and then back up again. It seemed kind of sporatic. I believe it was on the 2nd start that the PSI seemed to stabilize in the green and I thought my troubles were over, but then in the 3rd start it was sporatic again.

If anyone can give me some pointers as to what may be the issue I would greatly appreciate it. All of the other gauges seem to be fine. Could it possibly a grounding issue? If so, where do I look? Or could it be something else wrong?

Here are a few photos (if they post correctly) of my screen at various times and also the engine log graphs for the 1st three starts.

Thanks,
Nathan

https://lh3.googleusercontent.com/z...Z4-uo5ToLDKR2GmU36OiCGL7po2jeaqc=w800-h480-no

https://lh3.googleusercontent.com/j...PWwd6ZpoeMhjjkFv7J3EPaHAsnljnlD4=w800-h480-no

https://lh3.googleusercontent.com/3...ElnKMnpXSFOYvs79z3Tg-fTEX0Iwxeco=w800-h430-no

https://lh3.googleusercontent.com/0...HB8wMaqiCGCf_YEtILviQ_2r-DSxI4HI=w800-h437-no

https://lh3.googleusercontent.com/5...6j7H4AGpVkm7Po6Ny8KG3LDeNv1KxVGI=w800-h432-no
 
Grounds?

I am no expert but you seem to have a lot of things going on at once. If i were you i think i would review the grounds and sensor electricL isolations.
 
If there were a grounding issue, then it would seem that both cylinder head temperatures would be erratic, not just one of them. Still, it will not hurt to check the grounds, especially battery ground, voltage regulator ground, and G3X ground.
If the sensor wires have splices forward of the firewall, check those.
Check D-Sub connectors for loose pins or broken wires.
Good luck.
 
It does sound like you have some connection issues, except for the fuel pressure. There may be air in the line going to the sensor. With the engine OFF, turn on the electric fuel pump so you have pressure in the fuel system (mixture and throttle all the way off) and then loossen the fitting right at the fuel pressure sensor to bleed some fuel (and air) out of it. Then retighten it (don't forget to add torque seal), and check it again.

Vic
 
Contact Garmin

Based on your screenshots, it looks like you have an RV-12. Presuming you have the sensors that came with the Rotax 912 versus the sensors that come from Garmin, the issue could very well be grounding in the sensors. Some of the Rotax sensors ground through the engine versus directly to the sensor. I would recommend contacting Garmin support at [email protected]. Let them know which sensors you have and your grounding scheme. My vote is a ground issue.
 
The spade connectors used for many of the sensors at least on my installation (despite my best attempt) often were not well done. Suspect some of your issues might be addressed by checking all of those cheap connectors.
 
Issue Solved

So I went and checked all the connections of D-subs on the GEA 24 and the controle module. Everything seemed to be visually seated, but by chance I happened to bump the harness wires going to the control module and on the G3X I could see some instruments go on or off. So I did a more thorough check of the connections and found the the "EFIS" D-sub was connected, but not screwed tightly to the control module. I tightened it down along with double checking all others.

I did another run of the engine and the oil temp gauge stayed on, the CHT2 was showing, and the fuel PSI seemed to be stable. So these issues seemed to be solved at this point. Thanks for everyone's input. I was hoping it was something simple and it was.

Nathan
 
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