High and noisy tach reading

[vas4vans]

I have been stuck in India for a few weeks dealing with some parental health issues so a friend flew my RV-10 to an A&P to get the annual Condition Inspection done. On the return flight, he noticed that the tach was reading high (normal max is around 2660 and it was showing ~2900) and when I looked at the flight log data, I could also see that it was extremely noisy (as were the CHT readings).

Here's the logs from the last flight before the CI - https://apps.savvyaviation.com/flights/shared/flight/10748770/deee3737-054f-4e4e-864d-f350d4a24437
Here are the logs for the return flight f - https://apps.savvyaviation.com/flights/shared/flight/10748773/97d194f4-b5e3-4df8-b3f3-197aa8ab0ac7

The plane has dual Emags/Pmags with 2xAFS 5600. The Emag 12V output is connected to the AFS 12V tach input. The A&P indicated that he didn't make any changes there.

I had a similar issue about 6-9 months ago and it finally turned out that an ignition wire (from the Emag/Pmag) was not properly seated at the spark plug end which was causing the spark to jump causing significant EMI. The strange RPM behavior didn't show up when it was running on one of the ignitions (during a ground run-up) so it was obvious that it was being caused by an ignition wire on the other ignition.

I had the friend check the ignition wires and they seem to be seated ok though he did mention that the wires at the Emag end didn't look very good (photos attached). He also did a run-up on the ground but the behavior was the same on each ignition and seemed "normal" as best as he could tell but when he flew it again, it showed similar behavior again though this time the tach reading was not as noisy (though it was still high) - https://apps.savvyaviation.com/flights/shared/flight/10755869/480eb122-4f64-47a6-b29b-1ac6622c73b7 . Interestingly enough, some of the CHTs readings are still quite noisy.

It seems like an EMI related issue based on past experience but if anyone has any other ideas on what could be causing it, I would appreciate some input.

I am thinking of replacing all the plugs and the ignition wires after I get back next week.

Speaking of ignition wires, it looks like Spruce has a 60-90 day lead time for the Emag 6 lead ignition kit. I don't see anything on the Emag site that allows anything to be ordered. Does anyone know of an alternate source for the ignition lead kit? If anyone has built a set from parts available at an auto parts store, please send me the part numbers.

Thanks!

 

[lr172]

Initial experience should tell you that the emah supplied wires are sub par quality. Not the first to have issues. Better to replace with something better.

 

[Ralph Inkster]

Picture quality? Appears to have corrosion on the center terminal.
Can you slide the cable boot back a bit, than try plugging the terminal into the pmag coil housing. Does it wobble? Can you slightly pinch it for better connection?

 

[blaplante]

Also check that the engine ground is secure.

 

[vas4vans]

I finally got back my international travel and had a chance to do some troubleshooting. All the ignition wires were secured, ground connections were checked.

I also checked that the connectors on the EFIS were secure.

I then did a high power ground test with an optical tach to verify actual RPM. On the good news front, the actual RPM never went over 2670 (which is normal for this engine). The tach reading was fine until the power reached about 25" of MP but once I opened the throttle all the way, the tach reading started showing higher than the actual RPM up to a max of around 2930 (at all times, the actual RPM never went over 2670).

I also did an ignition test at high power to see if it was specific to one ignition but the results were the same on each ignition when the other one was off (tach drop on both was about the same). I then also pulled each alternator field breaker (the plane has two) to see if that could be causing it but that didn't show anything different (tach reading stayed above 2900).

It appears to be a noise related issue but only at high power settings. The noise also shows up in the CHT and EGT readings so it is not limited to the tach. I looked at the last flight done by my friend and it looks like the tach reading "settles" down when the MP is below about 23 inches but the CHT and EGT continue to be noisy.

Any other ideas on what could cause noise mostly at higher power settings?

Thanks.

 

[lr172]

I finally got back my international travel and had a chance to do some troubleshooting. All the ignition wires were secured, ground connections were checked.

I also checked that the connectors on the EFIS were secure.

I then did a high power ground test with an optical tach to verify actual RPM. On the good news front, the actual RPM never went over 2670 (which is normal for this engine). The tach reading was fine until the power reached about 25" of MP but once I opened the throttle all the way, the tach reading started showing higher than the actual RPM up to a max of around 2930 (at all times, the actual RPM never went over 2670).

I also did an ignition test at high power to see if it was specific to one ignition but the results were the same on each ignition when the other one was off (tach drop on both was about the same). I then also pulled each alternator field breaker (the plane has two) to see if that could be causing it but that didn't show anything different (tach reading stayed above 2900).

It appears to be a noise related issue but only at high power settings. The noise also shows up in the CHT and EGT readings so it is not limited to the tach. I looked at the last flight done by my friend and it looks like the tach reading "settles" down when the MP is below about 23 inches but the CHT and EGT continue to be noisy.

Any other ideas on what could cause noise mostly at higher power settings?

Thanks.

The higher the map, the harder it is for the coil to make a spark. Very common symptom back in the old, pre ei auto days. A failing coil would often only exhibit bogging under heavy acceleration.

I believe your problem is emi from ignition and most recent troubleshooting results just confirm that. Looking for high resistance. Could be coil wires or plugs. The fact thar the wires seem secure means nothing. They need to be ohm ed out while wiggling them around to replicate vibration.