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Ignition Noise

jump4way

Well Known Member
I'm looking for some ideas to squash an ignition noise issue I'm having. I'm able to isolate the noise by shutting off one ignition and the noise goes away. The noise is a steady tick tick tick noise that has an increase in cadence as rpm increases. The oddity is that If I turn on my aux input battery powered bluetooth module, the noise goes away.

Things I've tried are:
1) ferrite cores on the power leads.
2) two types of noise filters with the offending ignition power wired through.
3) replaced spark plugs (using solid tipped automotive spark plugs)
4) Ohm tested each of the ignition leads for proper resistance. They all checked out to show appropriate resistance for the given length. I also slightly twisted and rotated the leads as I checked the ohm reading to see if anything seemed amiss.
5) crimped each of the spark plug connectors to ensure good contact.
6) put dielectric grease on each of the spark plug caps.
7) checked the spark plug gaps.

Any other ideas any0one might have?
 
Check all ground wires on the whole aircraft for good terminations.
Make sure that the audio and mic jacks are mounted with insulating
step washers so that the jacks do not touch the airframe.
Quote from Bob Nuckolls' pdf:
p-lead shields should
be grounded to the airframe/engine only at the engine end. The
shield is used to provide a ground for the "GRD" terminals at
the switch but no other connection to the shields should be
made at the instrument panel end.
 
I'm using an electronic ignition but I suppose it's the same idea with the ground for the ignition coil in that it should be grounded at the engine. I currently have it grounded on my forest of tabs ground bus. I'll try a temporary ground to the engine and see if that makes a difference.

I have checked ground terminations and jacks for their respective shoulder washers.

Thanks for the ideas, please keep them coming.
 
Ignition noise

If it?s an LSE system then the forest of tabs works or if P-Mags ground directly to the engine, that?s always worked for me however follow the manufacturers instructions in the first instance;)
 
-snip-
The oddity is that If I turn on my aux input battery powered bluetooth module, the noise goes away.

-snip-

Any other ideas any0one might have?

I once worked with a guy that had a similar problem. He had a music input - a mini phono plug on his instrument panel - that picked up noise when nothing was plugged into it. We fixed the problem by making a terminating plug that had a resistor inside shunted across the input terminals.

Audio inputs tend to have very high impedance when nothing is connected to them, which makes them susceptible to picking up electrical noise. Loading them by connecting a lower impedance source "fixes" this.

You can test this theory by terminating your aux input with a resistance. As an experiment try just shorting the input terminals together. If that works you may be able to find a resistance value that when left shunted across the input stops the noise but doesn't cause attenuation of the audio signal from your Bluetooth module.

Good luck!
 
YMMV, but

I had the same tic with one of my mags (two slick mags) and it turned out the wire was slightly loose on the mag. It still shut off just fine. After buying a new capacitor, removing and tearing apart the mag and installing, that is what I discovered.

Slick parts are really expensive.

Good luck.
 
You never said what type of igntion you are running but did mention auto plugs.

Do you have dual electronic igntion? If so, what type?

Do you have a mixed ignition environment? If so, please describe.

If running auto plugs, what plugs and plug wires are you running?

Can you broadcast over your radio and be heard clearly?
 
You never said what type of igntion you are running but did mention auto plugs.

Do you have dual electronic igntion? If so, what type?

Do you have a mixed ignition environment? If so, please describe.

If running auto plugs, what plugs and plug wires are you running?

Can you broadcast over your radio and be heard clearly?

I'm using the SDS ignition system which is a dual electronic ignition system.

I am using the BR8ES 6391 plugs ( I think this is right... just going off of memory) with MSD plug wires.

I've had no complaints regarding transmissions.
 
If you have a hand-held VHF radio, you can check and see if the noise is on that too as it will be isolated from ship's power and grounds.
 
I once worked with a guy that had a similar problem. He had a music input - a mini phono plug on his instrument panel - that picked up noise when nothing was plugged into it. We fixed the problem by making a terminating plug that had a resistor inside shunted across the input terminals.

Audio inputs tend to have very high impedance when nothing is connected to them, which makes them susceptible to picking up electrical noise. Loading them by connecting a lower impedance source "fixes" this.

You can test this theory by terminating your aux input with a resistance. As an experiment try just shorting the input terminals together. If that works you may be able to find a resistance value that when left shunted across the input stops the noise but doesn't cause attenuation of the audio signal from your Bluetooth module.

Good luck!

Hmm.. interesting idea. I'm not sure I'm 100% clear on how you would wire the resistor. If I remember right, the plug is a stereo plug with 3 conductor wire so would I wire a resistor in line with each wire to the aux input?

Andy
 
Hmm.. interesting idea. I'm not sure I'm 100% clear on how you would wire the resistor. If I remember right, the plug is a stereo plug with 3 conductor wire so would I wire a resistor in line with each wire to the aux input?

Andy

Assuming the 3 conductor wire is 2 outputs + one return(common) it would take 2 resistors, connected between each output wire and the common. The value of the resistors should be low enough to eliminate the noise but not so low that your audio volume drops. That's why I suggested first just shorting them out - with no bluetooth module connected of course - to see if the noise goes away with them shorted but returns with them open.

This is not to say you don't have a noise problem - which you should definitely try to find and eliminate.

But if you have the same issue my friend did, it's like an antenna sitting there picking up every stray signal, which you most certainly don't want.
 
Noise

Are you running shielded spark plug wires?
Some electronic ignition setups use suppressor automotive type wires.
If that?s what you are using I would try using shielding on your wires.
Dave
 
I'm running automotive spark plug wires. I tried today disconnecting each spark plug wire one at a time while idling to see if I could identify a bad spark plug wire but the problem persisted regardless of which spark plug wire was disconnected.'

I think I can rule out the spark plug wires as well as the plugs. I'm going to try the above posted suggestion about shorting out the aux audio input and see what I get next. I'm thinking its in my audio system wiring somewhere.

I also tried the suggestion of using a hand held radio to see if I could hear the noise... I heard nothing over the radio. I notice also when I hear radio transmission, the ticking noise goes disappears. I only hear it with a quiet radio.
 
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You've probably eliminated the plugs and wires if you don't hear the noise on the handheld.

Try disconnecting the tach wire as this outputs a 12V square wave signal constantly with the engine running.

Also look at routing of the coil power and ground wires. Make sure these don't run close to antenna, headphone, intercom wiring. The instantaneous surge current is fairly high on these as the coils charge.
 
Ok thanks for the suggestions. I'll give that a try. I think the Power to the coil does run along the same side of the airframe as the headset jacks and aux audio input wires on it's way back to the battery bus. Maybe I can find a way to reroute that wire along the other side of the airframe. Sure glad I made the floors removable.
 
Fixed!

Just a follow up on my ignition issue. I was able to locate and resolve the problem today and as usual, it was something simple. The aux audio input was grounding out on the airframe as I had no shoulder washer for those. I cut off a snap bushing of the appropriate size to fabricate a shoulder washer and my problem is resolved. Thanks to all that offered suggestions.
 
Exact same issue resolved!

I also have the SDS CPI2 system with the same tick noise at idle. I searched the forum for ignition noise and found the solution to the noise.
I also have an aux audio input that was grounded to the airframe. When I had slick magnetos I had no ignition noise at all. When the offending aux audio input is removed from the ground the tick noise is completely gone and when I ground it the tick comes back.
Thanks for posting your solution it took all of about 10 minutes to fix it.

Kevin
RV-84KT
 
You've probably eliminated the plugs and wires if you don't hear the noise on the handheld.

Try disconnecting the tach wire as this outputs a 12V square wave signal constantly with the engine running.

Also look at routing of the coil power and ground wires. Make sure these don't run close to antenna, headphone, intercom wiring. The instantaneous surge current is fairly high on these as the coils charge.

Ross - would shielded two-conductor for power and ground on the mag coils be a good option here?
 
I?m not familiar with the SDS system but I fought the exact same problem with my Lightspeed EI system last summer. Turned out to be a failing coil.
 
Ross - would shielded two-conductor for power and ground on the mag coils be a good option here?

Hard to say. Most of these issues turn out to be something not right on the audio channels, a bad plug wire or junction at the terminal which is leaking or arcing to ground. Considering how many systems we sell, it's not a common problem and has been an easy fix outside of SDS- once you isolate what's causing it and that often takes some time and investigative work.

Kudos to the guys here for finding the cause and remedies.:)
 
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