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  #1  
Old 04-04-2020, 11:20 AM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
Posts: 947
Default Intermittent mis on ignition B

I have an intermittent mis on ignition B. I've done quite a bit of troubleshooting, new plugs, plug cap test, loose are damaged wires etc. I finally swapped the 2 top, horizontal connectors for A and B ignition modules input. Well the condition moved from B to A. If I am reading the prints correctly, that proves that everything from the spark plugs, through the ignition module is good. The problem must be between the ignition horizontal plug to the trigger coil for B. Wiring looks good so I assume that I either have a bad trigger coil, or the air gap is out of specs. Has anyone successfully tested and adjusted trigger coil air gap with an installed engine? Thanks for you help..........Tom
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1998- RV-9 tail kit, built and sold
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  #2  
Old 04-04-2020, 01:55 PM
todehnal todehnal is offline
 
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Well ****, I think my theory was wrong. I forgot that when I swapped the top horizontal plugs, that the ignition switch moved with it. So, if I have it right this time, since the mis moved from B to A, that proves that the trigger coils are working and the the problem is further down stream. So I guess it's back to the drawing board. My next task will be to swap the lower vertical plugs and see if it is the B module. Then keep moving down stream until it quits swapping from B to A.. Can you swap those vertical plugs without removing the intake manifold? Thanks.............Tom
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2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
1998- RV-9 tail kit, built and sold
1989- RV-6 tail kit, built and sold
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  #3  
Old 04-04-2020, 02:34 PM
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Piper J3 Piper J3 is offline
 
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At what RPM do you have the miss? I have same problem but only at lower engine speed. At 4000 RPM ignition test... engine is smooth on both A & B.
I changed plugs and caps with no improvement.
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Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 537

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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  #4  
Old 04-04-2020, 07:59 PM
todehnal todehnal is offline
 
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The mis is not rpm sensitive. However it feels worse at higher rpms. I’m getting about a 300rpm drop and it is as rough as a cob.
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2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
1998- RV-9 tail kit, built and sold
1989- RV-6 tail kit, built and sold
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  #5  
Old 04-05-2020, 04:03 AM
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Piper J3 Piper J3 is offline
 
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Don't overlook carburetion. Check weight of floats and also synchronization. If floats are close to 7 gram limit you can set floats out to “dry” for a few days. Reinstall “lighter” floats and see if it makes a difference. Check EGT’s to see how closely they match throughout entire speed range. Maybe switch floats L-R. Possibly running lean if circlip failed and allowed needle to fall. Needle could also be worn causing rich mixture. Check for vacuum leak - inspect rubber flange that mounts carb to intake manifold for hidden crack. Might be time for carb rebuild and thorough cleaning.
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Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 537

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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  #6  
Old 04-05-2020, 05:14 AM
todehnal todehnal is offline
 
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Hi Jim, Don't think it's vacuum since it runs so good on A ignition. I saw a blurb about pulling the enrichener on temporarily to see if it smooth out while on the questionable ignition side. That did not help. My first attempt to solve the roughness was to comply with the circlip bulletin. Also these are brand new floats (new style) and the weight is good. I had a float issue sometime back and it was easy to detect with a pool of gas on the drip tray. the drip trays are now nice and dry. Everything points to ignition. I have eliminated the trigger coils and ignition switches, so it must be further down the line. So I started with the easy stuff, new spark plugs, checked spark plug cap pull off and metered all of the plug wire sets, which verifies the secondary of the ignition coils. No joy. So, it must be somewhere between the vertical ignition connectors and the primary side of the ignition coils.
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2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
1998- RV-9 tail kit, built and sold
1989- RV-6 tail kit, built and sold
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  #7  
Old 04-05-2020, 08:30 AM
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Piper J3 Piper J3 is offline
 
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The plug caps are soft rubber compound. They are resistor caps and I feel that maybe with soft rubber the resistor gets damaged when pulling off spark plug - just a theory. I replaced my caps with hard plastic resistor caps. NGK - Spark Plug Resistor Cover - 90deg. Elbow Type (LB05F) 8051. I bought qty (8) on eBay for $50.

Also check spark plug wires for abrasion. There is several spots where wires touch brackets, etc.
__________________
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Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 537

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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  #8  
Old 04-05-2020, 10:27 AM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
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Made a tool for disconnecting the vertical ignition connectors and it worked. Swapped connectors and the roughness moved from B to A.
In studying the print, that says that the Ignition modules are good. I have already changed the plugs, tested the spark plug caps for pull off grip, and ohms tested the plug wire pairs, which also verifies that the coil secondaries and plug wires are good. So the problem must be between the ignition modules output to the coil primaries. Still not sure which one, but it is either the 3 & 4 top, or 1 & 2 bottom coil circuit. So what to do next.....Tom
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2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
1998- RV-9 tail kit, built and sold
1989- RV-6 tail kit, built and sold
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  #9  
Old 04-06-2020, 12:33 AM
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Piper J3 Piper J3 is offline
 
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Quote:
Originally Posted by todehnal View Post
I have already changed the plugs, tested the spark plug caps for pull off grip, and ohms tested the plug wire pairs, which also verifies that the coil secondaries and plug wires are good.
If the high voltage wires and caps check good for ohms there is still possibility that high voltage is "leaking" to ground during engine run. I remember seeing old car engines running at night with hood open and sparks imitating from the wires along their length. Capacitive discharge ignition used on Rotax is very high voltage with solid wires. Maybe look to see if wires have breakdown in insulation allowing high voltage jumping to ground. At one point I was going to change high voltage wires. Pretty sure they "unscrew" from coils just like caps "unscrew" at spark plug ends. High voltage solid wire should be available at auto store, racing shop, or eBay.

I'll keep following your thread. Please post solution when it is available...
__________________
-
Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 537

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H

Last edited by Piper J3 : 04-06-2020 at 12:37 AM. Reason: Added info on buying HV wire
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  #10  
Old 04-06-2020, 03:37 PM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
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Well, it's with my hat in my hand and egg on my face that I write this. I wanted everything back to original after swapping the vertical ignition cables before moving on to examine the high voltage coils. Somehow I got the connectors mixed up and had a devil of a time getting that straightened out, but I finally got it right. Of course I test ran it to verify. Someone posted a daunting Rotax ignition problem quite awhile back. After many hours of troubleshooting, the end results were that he had replaced a bad spark plug with a new defective one, and it took them down the garden path. Well, I guess I did the same thing. I had another brand new full set that I was saving to install when I had it running properly, but I decided that it would be well worth $25 to just do it, even though I had already replaced all of the B side spark plugs once. Well it ran like a top, and I actually was able to fly it today. It was a lot of work and I learned a hard lesson, but I did become quite familiar with the Rotax ignition system.

Sorry for raising the help flag and I appreciate all of the suggestions, It was a hard lesson, but I did learn a lot about the Rotax ignition system. I was finally able to fly today and I am a happy camper......Tom
__________________
2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
1998- RV-9 tail kit, built and sold
1989- RV-6 tail kit, built and sold
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