Light Speed ignition behavior

Still learning here... 40 years on mags and now in the 9 with an electronic ignition on one set of plugs. After about 20 minutes of flight (8500 ft) I hear a subtle change in the engine sound. Is the timing changing or maybe something else going on? It is barely noticeable, but I do pay close attention...

More info and tests?

I am running one mag one lightspeed. 400 hrs without an issue other than one small adjustment to mag.

I am no expert hopefully they chime in.....but you talk of a change in sound? Like what would you say it does?
Is there an RPM fluctuation, fuel flow change, temp change. Do you have a efis....if so download it and run it through something like savvy.

If you run in steady cruise and shut down the mag, still hear it. Turn mag back on and shut off lightspeed. Give some more stuff and the smart dudes will give you some good ideas.

flightlogic said:

Still learning here... 40 years on mags and now in the 9 with an electronic ignition on one set of plugs. After about 20 minutes of flight (8500 ft) I hear a subtle change in the engine sound. Is the timing changing or maybe something else going on? It is barely noticeable, but I do pay close attention...

Click to expand...

You should not hear any change in engine noise from your lightspeed ignition under any circumstances. The adjustments its making are far faster than your ear and brain can process as you are moving the black or blue knobs.

1000+ hours on dual Lightspeeds with flywheel pickups.

The -only- problem I ever had was when I developed an intermittent leak in the plumbing leading to the manifold pressure transducer. The ignition would try and adjust the spark timing based on the inaccurate readings it was getting.

Fixing the leak fixed the problem.

As usual... quick replies and very useful. Thanks !
Will check the plumbing to be sure that is not causing some timing change.
My original post said subtle changes. I really mean subtle. No change on EFIS, rpm or any other data I can see. But I can hear it. Guess it comes from three forced landings. I listen REALLY carefully to my engines.

Do an inflight magcheck

I also experienced a noticeble change in sound. Seemed some sort of a pulsing change in power. Had it for a few months, but there was nothing visible on the Efis or in the logfiles. On the ground the runup checks gave no indictions of any problem. But an inflight magcheck revealled that the electronic ignition wasn't firing properly. Changing the automotive plugs solved the problem.

+ 1 with Victor... try a new set of Spark Plugs.

Normally you cannot hear any change in engine performance if everything is operating normally with a Mag/LSI combination.

Are you sure that this is even engine related? You or your Pax just picking your heels up off of the floor will produce a change in sound or tone that could be construed as an 'engine noise' chance. The first time it happened in my -6 I immediately started looking at the engine monitor. I have chased more than a few noises down in RV's that were just caused by vibrational characteristics related to feet movement...

If you hear the 'change' and notice that your EGT's are spiking, then the LSI system has gone offline for some reason. (Breaker tripped, cable became disconnected, etc).

Dump your EFIS data and look at the time period that you described for any anomalies. That will tell you more than anything about the health of your engine.

Unfortunately unless you have the LSI Plasma III system you can't immediately observed the timing curve.

Joe,
Thanks for the detailed reply. Checked all the plugs but one. A misplaced egt probe is causing trouble in removing that one. Did check the vacuum plumbing and found a pinched line under a tie wrap. After re-routing the line I checked for rpm drop by pulling it off the vacuum source. Seemed to behave as it should.
The sound is subtle and not coming from the floor. Will investigate further and report back. On another thread, they are talking about carb heat. Do you know what kind of drop is expected in run up with a stock muff and electronic ignition?
Thanks for any advice.

Joe Blank said:

Unfortunately unless you have the LSI Plasma III system you can't immediately observed the timing curve.

Click to expand...

The LightSpeed manual states that both the LSI Plasma 11+ and the Plasma 111 will output the timing advance.

Light speed customer service

Last Friday night two plugs quit after a battery change. Klaus answered the phone on the third ring and helped with some suggestions. Cleaning the pins on the 9 pin connector at the back of the Hall Sensor cleared up the problem. Thank you Klaus! Battery had nothing to do with the problem, but it is distracting in the trouble shooting flow. New Irridium plugs in now and ready for a test flight after the helicopter convention.

I had an issue with my LSI last summer just a week before Oshkosh. My engine was starting fine, but would seem to intermittantly run rough - taxiing, runup, and in the air. I did the usual checks of plugs, mags, etc, but couldn't find the problem. With Oshkosh quickly approacing, I called Klaus at LSI and asked for help. After troubleshooting several items, he finally suggested that I check continuity on the ring gear magnetic sensor.

This could be done by unplugging the DB9 pin at the brain box, and checking for continuity as someone else pulls the prop through. I had continuity, but it seemed kinda flakey - once in awhile I would not have continutity.

I finally pulled the prop and removed the ring gear sensor and found one of the soldered wires had rubbed through the strain relief and had a break at the solder joint to the board. With no vibration, the wire was in contact with the board, but with any vibration or movement, the wire would rattle and the contact was hit-or-miss.

Klaus took the magnetic sensor board in on a next-day rush job, and got it mailed back to me in time for an on-time departure for Oshkosh just a few days later.

Long story - just another suggestion for troubleshooting.

Coil wire spade connector

On runup today noticed 200 rpm drop and bit rough on Lightspeed ignition...leaned and retested...still and after third time it seemed to clear up to smooth and less than 75 drop. In flight it seemed the 5 and 6 cyl egt were moving slightly more than normal. On landing did mag test and 5 and 6 were dead. Shut down and opened oil door to check spark wiring and coil. on inspection it seemed spade connector on coil was easy to remove so I crimped tight...Problem solved!! Now going back how long has it been intermittent inflight?

Jackm said:

On runup today noticed 200 rpm drop and bit rough on Lightspeed ignition...leaned and retested...still and after third time it seemed to clear up to smooth and less than 75 drop. In flight it seemed the 5 and 6 cyl egt were moving slightly more than normal. On landing did mag test and 5 and 6 were dead. Shut down and opened oil door to check spark wiring and coil. on inspection it seemed spade connector on coil was easy to remove so I crimped tight...Problem solved!! Now going back how long has it been intermittent inflight?

Click to expand...

Inflight engine noise change, it drives me nuts.

Thinking about investing in a Bose head set....