Electrical Interference Issue?

[802flyer]

HI all,

Hoping you might have some insight into an electrical issue I'm trying to track down. On the last few flights, I've noticed some erratic readings on various fields of my engine monitor (Electronics International MVP-50) during flight. The engine itself is running smoothly and making normal power, and aside from the transient spikes in data, all of the values otherwise seem to be in normal range.

I initially thought that perhaps the main DC bus might be fluctuating, thereby causing havoc with the analog/digital converters. However it seems that I'm getting spikes in sensor values even when the DC bus is stable. I also monitored the DC input voltage in the Aspen menu, which doesn't appear to be fluctuating (although I'm sure it's got some good filtering). I spoke to EI tech support who suggested that noise on multiple channels is likely due to EM noise/interference from some other accessory (alternator, ignition, etc.).

While Savvy is great for longer-term trends, it seems to smooth the graphs a bit and spikes are missed when looking at the full-length flight without zooming in. I've therefore been looking at the data in excel and have copied some graphs below. Some observations thus far:

 

This first graph seems to suggest that the majority of the noise showed up after leveling off and leaning (to LOP), then got better when I decided to abort the flight (richened the mixture and descended back to the airport). I had really started noticing the issues shortly after leaning then got better on descent, and this is  confirmed in the data. However there certainly are spikes before and after.

 

I did trial turning off the Alternator Field during the flight for around 15seconds to see if that affected things, as shown in the graph above. Unfortunately the issue persisted so I turned it back on.

  

 

I'm curious if anyone has thoughts on possible sources of interference that would get worse during leaning (despite lack of roughness). A shorter flight at low altitude (quick fuel run) did not show many errors at all. But subsequent flights at ~8000ft have continued to have somewhat regular errors.

Mags were IRAN'd a few months back by Aircraft Magneto Services and I've had a few tens of hours since before this issue started. The panel was apart for an Aspen install around the same time, but I've likewise been issue free for a few dozen hours since.

 

 

Above is a different flight, from yesterday. As before, it doesn't seem to become a problem until after I leaned out the first time. I then went ROP for a few minutes and that did seem to quiet things down. I then re-leaned to the same LOP setting and got the occasional error, but much fewer and farther between.

In this chart I zoomed in on the section where I tried mag checks and noticed that things seemed to repeatedly get better when running only on the left mag. But then after going ROP and back to the same LOP setting, I flew around for the rest of the flight with significantly fewer errors (such that I didn't have events regularly enough to try turning other stuff off). So I'm not sure if there's something about that first transition to LOP that is causing issues. And if there is some problem with the right ignition circuit, why did it more or less go away for the second half of the flight?

 

I'll be collecting and analyzing some more data, but figured this might be enough to start the hivemind churning. Thanks in advance for any opinions.

[N201MKTurbo]

I would suspect there is an intermittent short or open. These could drive the readings to full scale. 

[802flyer]

I don't disagree at all. But I'm puzzled why it's behaving somewhat predictably based on phase of flight, mag setting, etc rather than completely randomly. Hoping that can help narrow down where it is, but I haven't figured it out yet.

[EricJ]

Some things to check:

Grounds, for the engine monitor, sensors, etc.   Everything needs to be tight (secure) with clean contacts.

Ignition harness.    <- I suspect this might be a culprit.

P-lead shields.

Any loose grounds, shields, etc.

[EricJ]

2 minutes ago, 802flyer said:

I don't disagree at all. But I'm puzzled why it's behaving somewhat predictably based on phase of flight, mag setting, etc rather than completely randomly. Hoping that can help narrow down where it is, but I haven't figured it out yet.

One thing that is noisier at altitude than on the ground is the magneto.    It's why high-altitude mags are pressurized.

I suspect you're getting some ignition noise into the system, either from the mags or the harness.

[wombat]

My guess is you have some wire that has a resonant frequency with your cruise engine RPM.

Next guess is that at cruise speed and configuration you have airflow pushing wires around in the cowling.

 

So maybe try to cruise at a different RPM or different airspeed or configuration.

[802flyer]

5 minutes ago, EricJ said:

Some things to check:

Grounds, for the engine monitor, sensors, etc.   Everything needs to be tight (secure) with clean contacts.

Ignition harness.    <- I suspect this might be a culprit.

P-lead shields.

Any loose grounds, shields, etc.

I did crawl under the panel and all of the connectors seemed well seated, but it's so busy in there that it was a pretty cursory eval.

The ignition harnesses are brand new as of January (same time as the mags were IRAN'd) so I guess I should pull the cowl and make sure nothing is rubbing. I have looked them over a few times since the work was done and didn't see anything obvious, but will check the ignition leads and P leads more closely.

[802flyer]

6 minutes ago, EricJ said:

One thing that is noisier at altitude than on the ground is the magneto.    It's why high-altitude mags are pressurized.

I suspect you're getting some ignition noise into the system, either from the mags or the harness.

This is a good thought. I'll have a good look at the P-leads and ignition harnesses (new and hopefully un-injured per above).

[802flyer]

10 minutes ago, wombat said:

My guess is you have some wire that has a resonant frequency with your cruise engine RPM.

Next guess is that at cruise speed and configuration you have airflow pushing wires around in the cowling.

 

So maybe try to cruise at a different RPM or different airspeed or configuration.

I'll add the different RPM to my list of things to try, thanks

[Ragsf15e]

1 hour ago, 802flyer said:

This is a good thought. I'll have a good look at the P-leads and ignition harnesses (new and hopefully un-injured per above).

P leads are really sensitive.

Also check the security of your ignition leads where they attach to the plugs.  Those go just barely past finger tight and if they come loose, you can definitely get some weird stuff.  

[Ragsf15e]

1 hour ago, EricJ said:

Some things to check:

Grounds, for the engine monitor, sensors, etc.   Everything needs to be tight (secure) with clean contacts.

Ignition harness.    <- I suspect this might be a culprit.

P-lead shields.

Any loose grounds, shields, etc.

I think @EricJ nailed it here…

[Fly Boomer]

On 4/28/2023 at 10:45 AM, 802flyer said:

Mags were IRAN'd a few months back by Aircraft Magneto Services and I've had a few tens of hours since before this issue started. The panel was apart for an Aspen install around the same time, but I've likewise been issue free for a few dozen hours since.

I'm going out on a limb here, and suggesting that, if it's worse when LOP, you may be getting some wonky behaviour from your mags or wires regardless of when they were last worked on or replaced.

[802flyer]

I'm going out on a limb here, and suggesting that, if it's worse when LOP, you may be getting some wonky behaviour from your mags or wires regardless of when they were last worked on or replaced.

My instincts say you’re right, but I also feel like the electrical system is completely impartial to mixture setting. As long as the crank is spinning, the ignition system should be sparking just the same, regardless of how lean/rich the mix is.

But like I said, I share your suspicions even if I can’t articulate why.


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[Fly Boomer]

15 minutes ago, 802flyer said:

My instincts say you’re right, but I also feel like the electrical system is completely impartial to mixture setting. As long as the crank is spinning, the ignition system should be sparking just the same, regardless of how lean/rich the mix is.

But like I said, I share your suspicions even if I can’t articulate why.


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On reflection, I may be conflating LOP and high altitude, which can certainly stress magnetos.  I used to think I was a lot smarter.

[802flyer]

 

On 4/28/2023 at 12:21 PM, EricJ said:

One thing that is noisier at altitude than on the ground is the magneto.    It's why high-altitude mags are pressurized.

I suspect you're getting some ignition noise into the system, either from the mags or the harness.

 

On 4/28/2023 at 1:33 PM, Ragsf15e said:

P leads are really sensitive.

Also check the security of your ignition leads where they attach to the plugs.  Those go just barely past finger tight and if they come loose, you can definitely get some weird stuff.  

Was looking through my profile for an old post and realized I never closed the loop on this thread. EricJ and Ragsf15e absolutely nailed it. I found that an ignition lead had loosened up and must have been creating a lot of noise due to the intermittent contact. Once I torqued it (and double checked the others) back to spec, all of these issues went away. Thanks to the group for all the suggestions, and hopefully this might save some other poor soul a lot of time troubleshooting electrical noise.

[Ragsf15e]

1 hour ago, 802flyer said:

 

 

Was looking through my profile for an old post and realized I never closed the loop on this thread. EricJ and Ragsf15e absolutely nailed it. I found that an ignition lead had loosened up and must have been creating a lot of noise due to the intermittent contact. Once I torqued it (and double checked the others) back to spec, all of these issues went away. Thanks to the group for all the suggestions, and hopefully this might save some other poor soul a lot of time troubleshooting electrical noise.

Awesome! Easy fix!

 Had this happen once  as well and it took me a lot of googling to finally figure it out.  

Edited January 6, 2024 by Ragsf15e