FX3: intermittent zero amps, spiking oil temp, strobes tripping off

[cavok84]

I took delivery of my FX-3 in late March 2023 after the factory accomplished the 40-hour fly-off for me. Since then, I’ve put around 190 hours on the plane, the majority of which being comprised of sandbar and riverbed flying with some extended three to four-hour trips mixed in there.

The plane has been great, and it’s only somewhat recently that I’ve acquired a collection of issues that has me completely stumped. Initially, I thought these were minor isolated issues, but I looked at my g3x data recently, and now I’m concerned I may have a more significant problem.
I live and fly the plane in the southeast, so hot and humid, but it’s always been hangar kept.

Timeline
1. July ‘23- Oil Temp had always remained around 190 degrees; however, at the beginning of a three-hour flight, the oil temp oscillated fairly quickly between 190-225, with no change to oil pressure. I land and reseat the oil temp prope connections. After taking off again, the temp is running high but within limits (maintaining 195-210), about 10-15 degrees above expected but rapid oscillations stop.

2. The mixture cable spring that gives the knob detents when pulling out or pushing in breaks. The mixture knob isn’t freely moving, but it makes precision settings difficult when bumping around.

3. Nov ’23- Condition Inspection goes well. The oil and filter have been changed every 30-40 hours of flying with no issues noted.

4. March-April ’24- I begin noticing that my Strobe switch isn’t on mid-flight. Initially, I thought I was forgetting to turn it on, but it was around this time that I first saw the Strobe switch trip off during climb out. Very rarely, I will notice a brief dip to zero amps, followed by a rapid recovery of amperage (maybe a second at zero, if that).

5. Apr 23 ‘24- Due to the oil temp showing 15 degrees higher than ambient when turning on the IBBS (cold aircraft). I order a new oil temp sensor from Cub Crafters and have it installed by one of their Service Center mechanics. We also perform a thorough inspection of the aircraft and replace the mixture cable (Erroneously high oil temp reading is fixed).

6. Apr 23rd thru 30th- over the course of eight hours or so of flying, everything goes well. Oil Temp is back to 185-190, no oscillations; however, I begin to see the Strobe switch trip off more frequently. This doesn’t happen every flight, nor does it always happen more than once per flight; its highly variable.
I can’t correlate the behavior to anything in particular. It seems to happen in the pattern more often (high AOA, high vibration, frequent movement of throttle, etc.).
*However, I’ve seen the amp behavior with the Strobe switch off, and I’ve seen the Strobes trip without noticing amps dropping. (I’ll confirm this today)

7. April 30th, '24- During my last flight, shortly after liftoff, Oil Temp skyrockets, jumping from 190 to well past the redline in rapid oscillations. 190…280…190…300… blank….260….blank… etc. After completing the flight, the temp shows 195 at shutdown. Strobes didn’t trip.
The day after the flight, I do a runup. Temp shows 150 at a warm idle; however—above 1200rpm, the oil temp resumes the behavior, immediately jumping to the red and returning to expected normal (150 in this case) at low rpm.

8. I reviewed my flight data over the past couple of months) and noticed that amps typically hold at 2, sometimes 1, but occasionally hit zero (after zero, amps jump to 2 but sometimes 5…4….3…2). Looking further into the past, it seems this started quite a while ago (at least Jan), however occurrences are rare.

****
-Overall, I only saw the amp issue a few times on the g3x, probably because it only lasts a second or so, and most of my flying is eyes outside.
-My data logs at home for review are incomplete, and I’ll have more info once I download a complete history (e.g., when the amp drop began, changes to its frequency, what was happening at the time).
****

Considerations
Presently, I have a second, brand new oil temp sensor from CC in the event there actually is a problem with the sensor itself (this will be the second oil temp sensor replacement), but the amps hitting zero and Strobe tripping worry me.
-Could the Strobe wiring be shorting, causing the switch to trip off and interrupting alternator output (some sort of system surge to which the alternator output reacts)?
-Or is it more likely that I have an alternator issue which is shedding the Strobes?
-Or are they completely unrelated?
-Does the oil temp issue imply a greater electrical system problem?

I apologize for the wall of text, but I am a first-time aircraft owner, brand new to tailwheel and backcountry flying.
Tomorrow, I can follow up with some data logs if anyone has any ideas.

Thanks!


Cavok

[Andy]

Unfortunately the G3X data log may not be very useful for tracking down short duration intermittent faults. The recorded parameters are very heavily "lagged" and do not show short term transient events.

However, If you see a transient on the display it should be in the log as the display and log parameters appear to have the same, or similar, filtering time constants.

Check for any change in main bus volts (Main Volts/Volts 1) when the battery current changes. A check of a recent log shows steady 3 A battery current at 14.2 V in cruise flight with Wig/Wag and strobes on. My alternator current does show short term changes but alternator current is not monitored on a standard FX-3.

It may also be useful to look at all logged engine parameters during cranking for engine start. A sensor with a bad ground connection may show a huge spike in reading. The fact that your oil temperature issue was fixed by a sensor change but then came back seems to point to a bad connector. I'd suggest a careful check for proper crimping and contact pressure at any connection that was disturbed when the sensor was changed.

I had my strobe switch/breaker trip once. I replaced the switch/breaker and it has never happened since.

[cavok84]

Unfortunately the G3X data log may not be very useful for tracking down short duration intermittent faults. The recorded parameters are very heavily "lagged" and do not show short term transient events.

However, If you see a transient on the display it should be in the log as the display and log parameters appear to have the same, or similar, filtering time constants.

Check for any change in main bus volts (Main Volts/Volts 1) when the battery current changes. A check of a recent log shows steady 3 A battery current at 14.2 V in cruise flight with Wig/Wag and strobes on. My alternator current does show short term changes but alternator current is not monitored on a standard FX-3.

It may also be useful to look at all logged engine parameters during cranking for engine start. A sensor with a bad ground connection may show a huge spike in reading. The fact that your oil temperature issue was fixed by a sensor change but then came back seems to point to a bad connector. I'd suggest a careful check for proper crimping and contact pressure at any connection that was disturbed when the sensor was changed.

I had my strobe switch/breaker trip once. I replaced the switch/breaker and it has never happened since.

Thanks for the reply and advice.

So, shortly after writing this post, I began seeing amps going zero to negative and battery voltage dropping (e.g., 14.2, 14, 13.9, 13.8...). Eventually, I disconnected the aft strobe from inside the inspection panel (just a random guess), and the shorting stopped. The electrical interruptions and strobe switch tripping behavior stopped and hasn't returned since. So, I guess I'll need to replace the aft strobe assembly.

The oil temperature issue ended up being on the CC side of the wiring, not the temperature sensor side. After replacing the little connectors with ones that are a bit more robust, it hasn't returned.

Thanks for your help

cavok

[Andy]

A fault in the tail strobe could cause the strobe circuit breaker switch to trip. However, the alternator should be able to output at least 40 A while holding the regulated output voltage constant.

A defective strobe, or a strobe wiring problem, would not be likely to have any significant influence on the battery charge current. The strobe switch would trip before the alternator load became sufficient to pull down the alternator voltage.

You may have another electrical issue that is not related to the tail strobe.

[Pete D]

I would do a good visual inspection of your alternator installation. Check for;

• Belt tension
• Wire security, especially the small (orange) field wire, make sure it has a little slack and isn't pulled tight
• Alternator mounting bolts and arm security

I recently had one (not a new plane, several hundred hours) with occasional low (1 or 2 amps, occasionally zero) and slightly low voltage that inspection found loose alternator mounting hardware that was allowing low belt tension.

[ve6yeq]

The oil temperature issue ended up being on the CC side of the wiring, not the temperature sensor side. After replacing the little connectors with ones that are a bit more robust, it hasn't returned.

I was recently flying with TacAero and I had a similar issue in one of their FX-3’s that randomly flying base and/or final the CHT sensor on cylinder 1 would jump up impossibly quickly but once on the ground it would be back to the same as the other 3 CHT sensors. The TacAero maintenance staff there immediately suspected a loose crimp or splade connector as they had encountered many of these with their Carbon Cub’s that get a lot of heavy training use.

It was a great training exercise to learn to ignore the alert and just continue landing and then worry about the issue on the ground rather than spend attention on short final trying to reason about the alarm…

[cavok84]

Thanks for the advice, everyone.

As I said in an earlier post: I ended up disconnecting the tail strobe, which fixed the issue. This was around four months ago, battery charge has remained nominal, and AMP reading is back to normal (after starting engine, it settles around 4 and then drops to around 2 in flight). No more switch tripping.

I've kept the strobe disconnected, with the plan being to replace it and check all crimpings at each assembly in November during condition inspection.

*I did, however, miss the follow up responses to my post which suggest it may not be as simple as the tail strobe assembly.

And yesterday, during runup, I noticed the same thing happening (no tripping of the switch but amps going to 0 or -1) during the runup. It only occurred when above 1800 rpm, which made me think it is probably some of the crimping (high vibrations). While still running up the engine, the amps would immediately rise back to 4 or 5 when I turn the strobes OFF. Even if the alternator should be able to handle this, could a shorting cause such a reduction in battery charge?

I wish I had checked back here to read y'all's advice, because now I think it may be something else, as suggested. If 2 amps is on the low side, then my alternator has always had this issue. In flight and depending on what equipment I run (typically strobes, wig wags, sometimes servos) I see between 2 and 3 (with amps decreasing with additional load), with 4 being seen shortly after takeoff after having accomplished an engine start.

My condition inspection is coming up, but until then, I'll check the alternator and strobes more closely.

Does anyone have any suggestions for replacement strobes, if it is in-fact the assembly?

I would do a good visual inspection of your alternator installation. Check for;

• Belt tension
• Wire security, especially the small (orange) field wire, make sure it has a little slack and isn't pulled tight
• Alternator mounting bolts and arm security

I recently had one (not a new plane, several hundred hours) with occasional low (1 or 2 amps, occasionally zero) and slightly low voltage that inspection found loose alternator mounting hardware that was allowing low belt tension.

A fault in the tail strobe could cause the strobe circuit breaker switch to trip. However, the alternator should be able to output at least 40 A while holding the regulated output voltage constant.

A defective strobe, or a strobe wiring problem, would not be likely to have any significant influence on the battery charge current. The strobe switch would trip before the alternator load became sufficient to pull down the alternator voltage.

You may have another electrical issue that is not related to the tail strobe.

Andy and Pete, what are your thoughts on this given the effect of disconnecting the tail strobe and yesterday's issue with the strobe switch?

thanks!

[Andy]

AMP reading is back to normal (after starting engine, it settles around 4 and then drops to around 2 in flight).

I checked recent logs and found a peak of 18 A immediately after start. That was after a warm start about 3 hours after landing. The previous cold start with airplane hangared for several days showed a peak of 20 A. Very few of my start attempts require cranking for more than about 3 seconds. I have the SBS J16 battery.

What peak current do you see after start? Check the logs rather than replying on observing the peak which may only last for a few seconds.

If your alternator can supply 20 A to the battery immediately after engine start it should support any normal in flight load.

In flight and depending on what equipment I run (typically strobes, wig wags, sometimes servos) I see between 2 and 3 (with amps decreasing with additional load), with 4 being seen shortly after takeoff after having accomplished an engine start.

The battery charge current depends on the state of battery charge and the applied voltage. The MAIN bus voltage should be constant for any normal load you could add to the system. The battery charge current should be independent of loads.

Pete has given you some tips on checking the alternator system but, if you don't find any problem, you could remove the alternator and take it to an autopart store for test. I'd suggest you check they have capability before you remove it.

It's also possible that something is taking excessive current and pulling down the output voltage of a good alternator. I had a chafed alternator output cable on my PA-28 and it intermittently shorted to the crankcase. That took a while to find.

Reviewing data logs is a lot easier than pulling cowlings expecially in a hot hangar. I'd review a few data logs paying particular attention to "Volts /Volts 1" and "Amps /Amps 1". (I think those are the names of MAIN Bus volts and Battery current in a standard FX-3. I revised my names when I made avionics mods.)

Is Volts 1 constant in cruise flight and, if so, what is the value". If you see changes in Volts 1 do you see corresponding changes in Amps 1?

[cavok84]

I checked recent logs and found a peak of 18 A immediately after start. That was after a warm start about 3 hours after landing. The previous cold start with airplane hangared for several days showed a peak of 20 A. Very few of my start attempts require cranking for more than about 3 seconds. I have the SBS J16 battery.

What peak current do you see after start? Check the logs rather than replying on observing the peak which may only last for a few seconds.

If your alternator can supply 20 A to the battery immediately after engine start it should support any normal in flight load.




The battery charge current depends on the state of battery charge and the applied voltage. The MAIN bus voltage should be constant for any normal load you could add to the system. The battery charge current should be independent of loads.

Pete has given you some tips on checking the alternator system but, if you don't find any problem, you could remove the alternator and take it to an autopart store for test. I'd suggest you check they have capability before you remove it.

It's also possible that something is taking excessive current and pulling down the output voltage of a good alternator. I had a chafed alternator output cable on my PA-28 and it intermittently shorted to the crankcase. That took a while to find.

Reviewing data logs is a lot easier than pulling cowlings expecially in a hot hangar. I'd review a few data logs paying particular attention to "Volts /Volts 1" and "Amps /Amps 1". (I think those are the names of MAIN Bus volts and Battery current in a standard FX-3. I revised my names when I made avionics mods.)

Is Volts 1 constant in cruise flight and, if so, what is the value". If you see changes in Volts 1 do you see corresponding changes in Amps 1?

That's good to know. I think what got me caught with my guard down (regarding checking for Pete's and others' suggestions) was the fact that disconnecting the aft strobe solved my issues--until it didn't...

I flew this evening, and it did it again. I also had a line guy come up to me after my flight and tell me that my strobes were "continuously ON, and then they would flash again, then go back to ON (not flashing/strobing)".

That was interesting. As for my after start amps, I'll download the data and post here tomorrow. Based on what I see, I've never seen 20A. Occasionally, I'll see close to 15, but lately I see 7-8 (I have the earthx batt), but like you said--the data will tell the true story.

I had a flight to the Ozarks planned for tomorrow, but my concern is that if this is happening with the strobes OFF, then I have zero desire to leave the pattern and need to address this issue ASAP. I'll do a runup and lap around the pattern in the morning, upload the data, and see what is going on.

Thanks

Today during take off, amps remained at -2, and after leveling off and pulling the power and prop back, amps returned to around +2.

[hawgdrvr]

I believe this issue which has been going on a long time started while still under warranty. Why not ask CubCrafters to warranty replace all three strobes, or at least they should do it in good faith. If not, then determine the vendor for your strobes and ask them for replacements after explaining the issue. I don't know if there is a strobe controller like there is a wig-wag controller, doubt it, but you'd have to review or have Pete tell you the electrical diagram of this system. I hope CubCrafters will help you resolve this in a timely manner.