mmarmol

mmarmol

Member
I just bought my airplane. It has an electronic ignition on the "right mag" hooked up to the top plugs and a slick magneto on the left mag hooked up to the bottom plugs.
During the runup, at 1,700 RPM, when I turn off the magneto I get the usual 50 RPM drop and the engine runs smoothly. I then turn the mag back on and then turn off the electronic ignition. When I do that the engine RPM drops quite a bit but is still running fairly smoothly. I then turn the electronic ignition back on and everything comes back to normal.
Is this normal? Is my electronic ignition not working properly? I have always been a dual-mag guy so am a little scared by that behavior.

Thanks for all the expertise!
 
Miguel

From your description, the performance of your mag and elec ignition would seem to be normal provided that the rpm drop on mag only isn't too much. How much rpm drop do you get when turning off the electronic ignition?

A larger rpm drop when turning off the electronic ignition (EI) could be expected as the EI outperforms the mag.

The fix (if required) for this would be to replace the mag with a second electronic ignition.

Bevan
 
Agreed. Often, you will experience zero RPM drop when running on a single EI. When you say "quite a bit" of a drop on the mag only, that's the behavior you need to characterize. The EI sounds fine.
 
Hey guys,
Thanks for the response. I flew the airplane today. As far as quantifying the RPM drop there is an issue...my RPM readout is part of the electronic ignition. When I turn off he electronic ignition it turns off the RPM display so I'm not sure what the actual RPM drop might be. What I tried to do was to set the engine RPM at a number, then take it up to 1700 RPM and turn off the EI. I then compared this sound to the sound of the engine when I had set it at a lower RPM.
I think the results indicate that, when I turn off the EI, the engine RPM goes from 1,700 RPM to 1,200 or 1,100 RPM. Is this 500-600 RPM drop still in the acceptable range?

Thanks for the insight guys!
~Miguel
 
A 500 RPM drop is excessive! You should be looking into anything over about 150. A "normal" mag drop is 50-75 for a magneto, and 0-25 for an EI.

Make sure you are in fact dropping that much though. A 500 RPM drop would be extremely noticeable, even without a tach display. I can't see it dropping that much without running very rough.
 
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mmarmol said:
As far as quantifying the RPM drop there is an issue...my RPM readout is part of the electronic ignition. When I turn off he electronic ignition it turns off the RPM display so I'm not sure what the actual RPM drop might be.
Click to expand...

Head over to the model airplane store and buy an handheld optical prop tach (about $30). Quantify the RPM drop and report back.
 
+1 for Dan's suggestion. Get a prop tach that optically monitors the prop. Then tell us what you find.

As for how much RPM drop, my EI only drop is ~25RPM, the Slick mag only drop is ~75RPM.
 
One other consideration is that a number of people choose to put the electronic ignition on the bottom plugs to help minimize the rpm differential during mag checks. Bottom plugs can get more fouling and the electronic ignition deals with it better...
 
Timing

Keep in mind the EI has an advance curve that the Mag does not. ie the mag is always at 25, the EI base timing is 25 and advances with lowering manifold pressure. So a lot of the difference is due not to the hotter spark but to the shift in timing when switching from one to the other. 1700 rpm and partial throttle will probably produce some advance. A "mag" check at a lower rpm will likely produce an even larger difference in the two systems while one done at WOT near SL will probably have less.
Check out Mike Busch's in flight mag check once you get comfortable with your systems. It's much more effective in revealing ignition system problems.
Tim
 
There is an ElectroAir ignition in place of the right mag on the RV-6 I just bought. It's wired to the bottom plugs, are you sure yours isn't? Not really relative to the discussion perhaps...

Anyway, when I did the pre-purchase inspection there was nearly no RPM drop while running on the EI/turning off the left mag on the initial run-up. There is a mechanical tach in this airplane, so no issues monitoring RPM. I would also encourage you to find a better tach solution as well.

We flew the airplane as past of the pre-buy, and on the first take-off attempt had a fairly significant stumble from the engine during acceleration. On the ground a run-up confirmed rough running on the EI. We found a slightly shorted lead inside the plug barrel in one cylinder, and a slug of oil in the MP line to the MP sensor. The sensor is positioned in such a way that it's at the bottom of the line and any oil will run down into it. After troubleshooting the ignition system and fuel system thoroughly, those were the only issues we found. Further run-ups were smooth since the short was repaired, but had an essentially equal RPM drop of 50 to 75 RPM on both the mag and the EI. Disabling the MP sensor has no effect at all, indicating that it is inoperative. We changed the plugs during that initial troubleshooting, and I've since changed to some Accell wires and swapped in some Autolite 386 plugs, again with no change. I've talked with Mike at ElectroAir and he seems confident that it's the MP sensor as well, so I have ordered a replacement.

Your situation sounds far worse, if you're getting an RPM drop as severe as you describe it's certainly not flyable. I second (third, whatever) the idea of getting some type of tach reading ASAP so you know where you're at. You indicate that it runs smooth, so perhaps that RPM drop isn't as bad as you think. The short we found was from the "spring" insert protruding through the insulation and shorting inside the barrel of the plug, it wasn't terribly obvious so look closely.

Part of the basic troubleshooting we did was to verify good connections and ground for the EI, make sure you check all those basic items.

Good luck and let us know what you find.

Doug
 
Fellas (and ladies?)
THanks for the wealth of replies...I spent most of the day today doing troubleshooting and have some things to report.

As a quick summary my issue was that when I turned off the magneto I got the usual 50 RPM drop but when I turned off the EI I got a drop that sounded like ~500 RPM.

1. I went out and bought the optical propeller counter. When I turn off the EI, sure enough, the RPM drop is around 450-550 RPM. The engine does run a little rough.

2. Thinking that this obviously means the magneto is toast I swapped the magneto with another one that is waiting to be installed on another aircraft. I got the SAME effect!!!

3. Triple-checking the magneto timing showed me that it was timed perfectly a 20 degrees BTDC like my engine asks for in the data plate.

At this point I guess the culprit is the EI but, since I did not install it, am not sure what the troubleshooting steps to follow should be. Any ideas you guys can provide?

As far as getting an RPM reading that is independent of the electronic ignition I have a Dynon system on order that will include that RPM reading so it will take care of that problem. I also don't like depending on the EI for the RPM.

Thanks everyone for all the replies so far!

~Miguel
 
Check the plugs and wires (particularly the ones that the mag is firing).

The EI is performing better than the mag.

Bevan
 
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I know you said your data plate states 20 degrees BTD.
What kind of engine set up do you have that requires 20 degrees vs. 25 degrees?

Try a run up at higher RPM even 1800 will yield a change in mag drop behavior.

At this point I guess the culprit is the EI but, since I did not install it, am not sure what the troubleshooting steps to follow should be. Any ideas you guys can provide?
Click to expand...

Your EI is not to blame for a mag drop when you turn it off, its running perfectly. Your problem is squarely with the mag.
 
mmarmol said:
...At this point I guess the culprit is the EI but, since I did not install it, am not sure what the troubleshooting steps to follow should be. Any ideas you guys can provide?...
Click to expand...

Not sure how you draw that conclusion... It sounds like the EI is the one thing working correctly. You swapped out the first mag and got the same result... What remained the same? Plugs and wires. Time to inspect and ohm them out.

Another factor that may help is to lean the engine at run up. At my altitude of 2600 feet, I can usually get a 30 RPM increase at 1800... Once I get that, THEN I do the "mag check". It looks like you are not at any significant altitude, but you may be fat anyway. Just lean the engine until you find max RPM and it starts to drop, then back off rich just a hair (back to max). It sure wont bring back your lost 500 RPM, but it may help.
 
Advanced at idle

Put an automotive timing light on the EI, you will see something like ~40 degrees of advance at idle. The timing light will not work on the Mag wires as they are shielded but if they are set correctly they will be at 25 or whatever for your engine, you said you've checked already. That extra advance from the EI will produce a lot of rpm at idle. You can also unplug the manifold pressure line to the EI, plug the line to the engine side only and it should drop back to base timing, same or close to the mag, then you should see a much closer drop between systems. If not check out the rest of the mag side ignition, plugs, wires etc.
Tim
 
OK, I feel a little silly that I didn't think to look at the plugs and magneto wires...I have all of a week's experience wrenching on airplane engines :eek:. I guess there's only one way to learn though :D
I will be out of town for work for the rest of the week but I will check my plug resistance when I get back. Depending on how that goes my next step would be to replace the magneto harness.

Thanks for all the assistance so far. This has been a tremendous learning experience and I've had the airplane for just over a week :)
 
Another data point

If have efii on the lower plugs and a new mag on the top. Mag timing is dead nuts. From 1,800 I get a out 120-130 rpm drop for either side. Both perfectly smooth, everything is running gr8. I have EIS 4000 giving me rpm.

Interestingly when I look at my engine data on savvyanalysys.com the mag rpm is always exactly some number (forget exactly) like 150 rpm higher than the electronic, which of course cannot be.
 
Hey everyone!
I just wanted to post on the progress of troubleshooting the runup/RPM drop issue. After taking out the four bottom plugs I measured the resistance and got the following numbers:

#1: 1kOhm
#2: Infinity
#3: 3kOhm
#4: Infinity

I went ahead and changed out the four bottom plugs and proceeded to do another engine runup. Unfortunately this did not fix my issue as I am still seeing a 400-500 RPM drop when I turn off the electronic ignition. My next step is going to be to change out the mag ignition harness since it is the only part of the system that has not been changed.
If that doesn't fix it I am concerned about what the possible causes could be since it starts to possibly be an engine internal issue.

Thanks for all the great suggestions and support so far!
 
What engine is it that you have?

20 degrees BTDC is not normal for the kind of engines in RV's. This may be correct if you have some kind of Turbocharged TCM or Chieftan engine, but not the typical IO360/540 in an RV.

The next thing is use a Rite System digital timing device and get the procedure right.

I suspect this could well be the problem compared to the EI.
 
See post #15
I know you said your data plate states 20 degrees BTD.
What kind of engine set up do you have that requires 20 degrees vs. 25 degrees?
Click to expand...

We all want to help, did you run up your engine at higher RPMs <1800>
and lean to the max for run up.

Make sure your try all that first and please double check your mag timing, 20 degrees BTC is really not normal for a NA engine.
 
So the engine is an O-235-L2C. Due to your earlier post I did go back and check other sources to cross-check what it said on the data plate. On the operations manual for the engine (http://www.flugsportvereincelle.de/downloads/iw-o-235ando-290.pdf - see page 19 of the PDF) it also says 20 deg BTDC.

I will try and do a runup at 1,800 RPM with and without leaning today or tomorrow and see what I get. I will also try and do another magneto timing check and make sure the mechanic didn't make a mistake last time but that will take another couple of days since I have to borrow one.

Thanks everyone!
 
The 0-235 L2C is in fact listed as an engine with slick mags and timing set at 20 degrees BTDC. That would be a 8.5:1 Compression and max 2800 RPM for take off.
Could it be that your LSE is mounted at 25 degrees BTDC.
Easy way to find out, you'll need a strobe light and read the instructions on LSE's website. If the idea of standing next to a running engine with a stobe light bothers you, you could set your mag to 25 degrees BTDC just for the purpose of a run up and see what the drop is then. If the drop is close at that setting you'll know the LSE is mounted incorrectly. That would have been an easy mistake to make for a builder when 95 % of all engines have their timing at 25 BTDC. None of this will cost you anything and is worth a shot before you buy new components.
You said you did not build the plane.
What does the previous owner say about it? Has it always been like that for him or is this excessive mag drop something new since you bought it?
 
Hello everyone!
just wanted to double back and close the loop here in case anyone finds themselves in a similar bind.

I replaced the magneto wiring harness a couple of weeks ago and the problem went away; I now get the appropriate 125 RPM drop! :D

So it turns out that was my problem after all.

Runs like a kitten now!!

Thanks to all f you who helped me through this!

~Miguel
 
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