Garmin G3X RPM erratic issue after Bendix Dual Magneto D4LN-3000 / 10-682555-11- 500hrs inspection.

[Minivation]

I'm installing a GI275 EIS with GEA24 on a Piper Saratoga SP (PA-32R-301T), also with a D3000 dual mag, and having the SAME issue. The RPM works OK until I reach about 2350rpm, at which the tach goes erratic and jumps +/- 100rpm. The problem persists regardless of which mag I select on the ignition switch, but goes away when I retard the power below 2350rpm.

So far, I have checked (1) proper pinouts and installation of proper in-line resistors per Garmin's manual, (2) proper supply of power and clean ground at the GEA24, (3) proper shielding and ground return of the p-leads, and (4) proper contact of the P-lead compression fitting to the mag itself.

I have even refabricated the entire P-lead and RPM pickup cables from scratch. So far, none of these have solved the issue. Garmin support suggested doing a factory reset of the EIS (which I did) but that did not yield results either.

Just adding one more case study to the list. I'll bring updates once we solve this issue.

[Shawn26]

19 minutes ago, Minivation said:

I'm installing a GI275 EIS with GEA24 on a Piper Saratoga SP (PA-32R-301T), also with a D3000 dual mag, and having the SAME issue. The RPM works OK until I reach about 2350rpm, at which the tach goes erratic and jumps +/- 100rpm. The problem persists regardless of which mag I select on the ignition switch, but goes away when I retard the power below 2350rpm.

So far, I have checked (1) proper pinouts and installation of proper in-line resistors per Garmin's manual, (2) proper supply of power and clean ground at the GEA24, (3) proper shielding and ground return of the p-leads, and (4) proper contact of the P-lead compression fitting to the mag itself.

I have even refabricated the entire P-lead and RPM pickup cables from scratch. So far, none of these have solved the issue. Garmin support suggested doing a factory reset of the EIS (which I did) but that did not yield results either.

Just adding one more case study to the list. I'll bring updates once we solve this issue.

My setup was working fine till the mag was removed for 500hrs inspection. I did everything you done! No changes. 
Unfortunately with D-3000, P-lead is the only source for getting TAC and RPM. I wish UMA would have made RPM sensor for the dual mag for certified aircraft. JPI makes one, and it’s the most reliable and precise way to get the information from the magneto. UMA have one for none certified aircraft for D-3000. I spoke to their technician and I was told many shop install them on certified aircraft but that’s not the route I like to take. 

I guess we have to stick to the P-lead for now and figure out what needs to be done! My shop suggested to change to new GEA24 version as advised by Garmin. I doubt that solve the problem! 

Please update if you come across of new information. Thank you. 
 

 

 

[Minivation]

I just came back from the shop after adding capacitive filters to see if that helped. It did not.

At this point we are running out of options, and running out of time (the aircraft is due for an annaul at the end of this month).

Out of curiosity, what would the UMA sensor that is reportedly compatible with the D-3000 be? As Jetdriven mentioned, the issue behind trying to use a UMA hall-effect pickup is the fact that it spits out two pulses per engine revolution. This would not be a problem if Garmin incorporated a pulse ratio software setting, but evidently that is not on their radar.

If things get really bad, I forsee a need to remove the GI275 and install a JPI instead.

[Shawn26]

2 minutes ago, Minivation said:

I just came back from the shop after adding capacitive filters to see if that helped. It did not.

At this point we are running out of options, and running out of time (the aircraft is due for an annaul at the end of this month).

Out of curiosity, what would the UMA sensor that is reportedly compatible with the D-3000 be? As Jetdriven mentioned, the issue behind trying to use a UMA hall-effect pickup is the fact that it spits out two pulses per engine revolution. This would not be a problem if Garmin incorporated a pulse ratio software setting, but evidently that is not on their radar.

If things get really bad, I forsee a need to remove the GI275 and install a JPI instead.

I don’t know the UMA part number, but they have one for D-3000 magneto for none certified aircraft. UMA tech-support mentioned they are lots of people using it on certified aircraft, he didn’t know how. Obviously Garmin is not supporting it or provide any guidance on installation. 
 

I dropped off the airplane at my Avionic shop. If I get any update on the progress I’ll repost about it. I’m down two months. obviously, I’m not happy about it. We just have to see whats causing this interfering. I’m sure Garmin knows about this issue as I’m not the only one! 

[Thedude]

This is terrifying me, I have a g500txi as the only engine monitor and my dual mag is coming up on it's 500 hour and I was trying to figure out how to get the mag to van nuys until this thread popped up (the plane is new to me as of September, so I haven't gone through any of this yet).

[Shawn26]

3 minutes ago, Thedude said:

This is terrifying me, I have a g500txi as the only engine monitor and my dual mag is coming up on it's 500 hour and I was trying to figure out how to get the mag to van nuys until this thread popped up (the plane is new to me as of September, so I haven't gone through any of this yet).

I believe your engine information EIS works the same exact way as my setup. You don’t have a separate sensor for tac / RPM and the P-lead is the only source of information for your dual mag. You may come across of the same issue I’ve encounter. 
 

i just hope Garmin can figure out the problem and provide alternative solution really soon. 

[jetdriven]

Well, they refused to use the UMA sensor because it said it wasn’t PMA or STC. But the P-leads are a substandard solution for Rpm pick up.

[Minivation]

10 hours ago, jetdriven said:

Well, they refused to use the UMA sensor because it said it wasn’t PMA or STC. But the P-leads are a substandard solution for Rpm pick up.

I understand that logic. I see UMA also makes a tach generator that taps in to the original tang drive (T1A3-4) and that is TSO'd. Legalities aside, the technical issue still remains: the unit would output 2 pulses per engine revolution so unless Garmin adds a provision to define a sort of "K factor" for this, this solution will not work.

[Minivation]

@Shawn26 Does your Mooney by any chance have a turbocharged Lycoming 540? The Saratoga I'm dealing with has a TIO-540-S1AD that goes up to 36" at sea level.

I just noticed in some of the video documentation from my run-ups that my "2350 rpm" border so happens to correlate where the MP exceeds atmospheric (roughly 30" where I am). The Bendix D3000 on this plane isn't pressurized, so I can't see a valid reason why MP would affect the magneto's operation, but it's something that got my attention.

[Shawn26]

49 minutes ago, Minivation said:

@Shawn26 Does your Mooney by any chance have a turbocharged Lycoming 540? The Saratoga I'm dealing with has a TIO-540-S1AD that goes up to 36" at sea level.

I just noticed in some of the video documentation from my run-ups that my "2350 rpm" border so happens to correlate where the MP exceeds atmospheric (roughly 30" where I am). The Bendix D3000 on this plane isn't pressurized, so I can't see a valid reason why MP would affect the magneto's operation, but it's something that got my attention.

No, the Mooney it’s not turbo charge. I’ve IO-360. 

[Minivation]

We received a response from Garmin aviation support, which basically can be summarized to "the magneto is at fault."

I don't disagree with that statement -- perhaps there is something inside the magneto that is causing the P-lead pulses to become unreliable, but our testing of the magneto with reference to its functionality for the engine reveals no immediate airworthiness concerns. RPM drops at prescribed run-up checks are nominal and the classic mag ground check is OK as well. It goes without saying the magneto timing to the engine is OK as well.

In my contact with them I also asked them if they had any intention to add alternative methods to interface RPM, but they have ommitted this question altogether. To be fair, I don't expect Garmin to somehow make their P-lead RPM pickup interface more reliable on their end, but I most certainly would appreciate it if they seriously looked into a tang-driven pulse generator solution that would (1) offer Bendix dual mag operators a known, low-risk alternative to the P-lead pickups, and (2) be a solution that would be nearly universally applicable to any piston engine.

For now, it has become my policy not to recommend the Garmin EIS for dual magneto-equipped aircraft until more options are made available for them.

[Shawn26]

20 hours ago, Minivation said:

We received a response from Garmin aviation support, which basically can be summarized to "the magneto is at fault."

I don't disagree with that statement -- perhaps there is something inside the magneto that is causing the P-lead pulses to become unreliable, but our testing of the magneto with reference to its functionality for the engine reveals no immediate airworthiness concerns. RPM drops at prescribed run-up checks are nominal and the classic mag ground check is OK as well. It goes without saying the magneto timing to the engine is OK as well.

In my contact with them I also asked them if they had any intention to add alternative methods to interface RPM, but they have ommitted this question altogether. To be fair, I don't expect Garmin to somehow make their P-lead RPM pickup interface more reliable on their end, but I most certainly would appreciate it if they seriously looked into a tang-driven pulse generator solution that would (1) offer Bendix dual mag operators a known, low-risk alternative to the P-lead pickups, and (2) be a solution that would be nearly universally applicable to any piston engine.

For now, it has become my policy not to recommend the Garmin EIS for dual magneto-equipped aircraft until more options are made available for them.

I sent you DM. Wondering if you can contact me. Thank you

[Thedude]

@Shawn26 any update? Are you still stuck?

[adamb.hicks4]

Yes, any update?  I am also curious as I have purchased a Dakota with the dual mag and am planning to install the GI 275 EIS.

[Shawn26]

14 minutes ago, adamb.hicks4 said:

Yes, any update?  I am also curious as I have purchased a Dakota with the dual mag and am planning to install the GI 275 EIS.

Besides becoming increasingly expensive due to labor and diagnostics, there has been no update.

We removed the new 500-hour magneto, sent it to the shop, and they replaced the bearing and contacts components that had already been serviced at 500 hours. We then reinstalled it on the airplane, but there was no change, RPM still erratic. 

We replaced the entire P-lead wires, but still, no change.

The next step is to rebuild a new magneto and install it. I’ve come across a few others on social media with the same issue with the dual mag. This situation is becoming really frustrating, as I've been grounded for about three months. 

 

---

Let me know if you want any further refinements!

[adamb.hicks4]

Good luck.  Sounds like a very frustrating situation. 

[Shawn26]

Just now, adamb.hicks4 said:

Good luck.  Sounds like a very frustrating situation. 

Absolutely! A little luck is all I need. 

[jamesyql]

I was considering a garmin upgrade but instead (along with budget constraints) adding some sensors to my 730 for now. Interested to hear progress along the way here and thanks for sharing. Sorry you are going through this.

[Thedude]

How hard is it to throw an old tach in the plane not really mounted anywhere if this problem doesn't get figured out soon?

I have no idea what's involved in the process here.

[Shawn26]

5 minutes ago, Thedude said:

How hard is it to throw an old tach in the plane not really mounted anywhere if this problem doesn't get figured out soon?

I have no idea what's involved in the process here.

I presented this option to the avionics shop, but they responded that the system is working, despite some arcing and distortion. Installing a secondary RPM and tachometer is not ideal. There are plenty of airplanes with the same dual magneto setup that have no issues. Recently, Garmin has received numerous inquiries about erratic RPM readings related to P-lead installation on dual magneto systems, and I believe they are working on a solution soon. 

[EricJ]

Sounds to me like it's not the mag.    The pickup and process that JPI uses with the dual mag has been rock-solid in my airplane, but it uses a sensor over the magnet rather than the p-leads (which can be noisy, anyway).

 

[Shawn26]

6 minutes ago, EricJ said:

Sounds to me like it's not the mag.    The pickup and process that JPI uses with the dual mag has been rock-solid in my airplane, but it uses a sensor over the magnet rather than the p-leads (which can be noisy, anyway).

 

I know that JPI has a sensor, and I believe I had one prior to installing my new avionics. Unfortunately, the Garmin G3X is only certified with the P-lead for the bendix dual mag. So im out of options and I’d prefer not to reinstall the JPI just to resolve this issue.

[Thedude]

1 hour ago, Shawn26 said:

I presented this option to the avionics shop, but they responded that the system is working, despite some arcing and distortion. Installing a secondary RPM and tachometer is not ideal. There are plenty of airplanes with the same dual magneto setup that have no issues. Recently, Garmin has received numerous inquiries about erratic RPM readings related to P-lead installation on dual magneto systems, and I believe they are working on a solution soon. 

I would just want to get my plane back up in the air, so it's not ideal, but way better than sitting on the ground.

[Shawn26]

1 minute ago, Thedude said:

I would just want to get my plane back up in the air, so it's not ideal, but way better than sitting on the ground.

You're absolutely right, and I'm tired of it too. We're taking two steps to troubleshoot the issue. If these don't work, I'll go that route.

1. Replacing the old GEA24 with a new version to see if the problem persists.
2. Reinstalling a newly rebuilt magneto.

Hopefuly one will work! 

[Thedude]

Any update on this?