"mag drop" Troubleshooting

[ls6pilot]

Just finished changing oil and replacing spark plugs. No problems prior. 

Now:

300-400 rpm drop when on mag 2. 50 on 1. Previous 50 on both. 

Checked all plug connectors to make sure well seated and secure. I have looked at troubleshooting info but could use advice about how to proceed. 

No recent work on carbs. 

Bad plug? 

Thanks in advance.

Rich

[DHeal]

If you have an EGT probe on each of the four cylinders, you should see a rise* in the EGT temp on the cylinder with the misfiring spark plug/lead.  Check that cylinder's spark plug's resistance (http://www.ngk-sparkplugs.jp/english/techinfo/qa/q08/index.html) or just replace the suspect spark plug.  In addition, you could trim off the end of the plug's lead and reset the plug's connector.  

* The inefficient and prolonged burning of the single-plug combustion gases causes the EGT to increase.

[ls6pilot]

Does the spark plug connector/cap screw off allowing one to trim the lead?

one  egt probe so not sure how to isolate which cylinder.

With ignition switch in 2 position which 4 plugs should be firing?

 6 of the plug wires look new while the lower ones on 1 and 3 look old.

 

 

[ls6pilot]

Bump

Anybody want to help me out here?

Here's my plan. While running set to mag 1 and use ac current tester to id which plugs are firing and then I will know which plugs are firing on mag 2. 

Turn to mag 2 and us ir temp gun to identify which cylinder is not firing. Check plug and cut and rescrew plug wire.

Does that sound reasonable?

Thanks 

Rich

 

Thanks,

Rich

[MEH]

My mechanic once told me that if I was doing a mag check at run-up (on a Lycoming or Continental engine) and one mag had that kind of drop, I should taxi back to the hangar on that mag, shut down, uncowl, and grab the IR Temp thingy and which ever cylinder was significantly lower in temp...... For Rotax, I would maybe uncowl and while parked and at idle leave it on the rough mag and grab the IR Temp gun and find out which exhaust coming from the cylinders was the coolest.  If you leave it running on the rough mag, the cylinder which is the culprit would presumably not be making spark and therefore no combustion, hence cooler.   Just watch the spinny thing out front.

[DHeal]

I do not know how your ignition modules control switches ("mags") are specifically wired in your aircraft.  The ROTAX 912 Major Maint Manual has the generic wiring diagram for the ignition system.  Knowing which of your switches controls which module/set of spark plugs will aid you in your troubleshooting.  You could just replace all of the newly-installed spark plugs with the old used set of proven spark plugs (or a different set of new spark plugs) and see if the problem goes away.  If the problem persists, perhaps trimming of the ignition leads is in order.  The connectors "unscrew" from the wires.

[Buckaroo]

It might be a dreaded failing ignition module as well. Mine started with needing ice packs to start then one day at run up when I went to check the 2 mag at 3400 rpm she immediately died. Carmo!!

[ls6pilot]

Yeah I hope not. I'm just hoping that with the timing right after plug change that it is something simpler (and cheaper)

I will definitely give Carmol a try if it comes to that. 

Thanks

[cdarza]

Short version:   Did a  "Mag check"  and on #2 switch, the engine completely died.   Restarted and tried it again and #1 switch would have the normal 50rpm drop-   Check#2 -engine died again.   Opened up cowl to "check" -  dunno what I was really looking for - maybe a lose wire /plug off or anything that might indicate the problem -- Nothing.      Decided to try running engine again - and it ran fine with no engine stoppage on either #1and #2 mag switch.   I don't want to fly and won't fly until I figure this one out.   Where is best to start and what am I looking for ?    (ref picture)  Should  I start here by removing  the connectors and checking  the wires ?

Long version: This mag check actually happened when I landed after a 3 hour flight.   2 hours into the flight I felt like something with the engine wasn't quite right.  Was humming along at 5000rpm and kinda thought I saw the rpm drop 50rpm but immediately go back up.   This happened a few times but it was barely noticeable so I tried the carb heat and also thought maybe some dirt in the carb was causing this     -again,  no significant drop or loss of power to really be concerned about but I just had this feeling that it wasn't normal.  Tried full power and I was getting it but it also felt a bit lower than what I was used to.    Finally landed and thats when for some reason I just thought of doing a mag check and thats where the first part of the story begins......     Argh,  wish the #2 would still cause engine stoppage as that would be easier to confirm the cause.   

[Tom Baker]

Three things come to mind. First a bad ignition module. Unless you have had your repaired they appear to be original to the airplane, and there has been a known issue with modules from this time frame. however complete failure is a rarer issue than most have. Second is the "P" lead. It is possible that the "P" lead from the module to the ignition switch has a spot where the insulation is worn through, causing it to ground out keeping the module from firing. Lastly it could be a problem in the switch itself. This is the least likely, but is still a possibility.

[Tom Baker]

Replacing the "P" leads will be the easiest and cheapest thing to address first. The only problem is that you will need to order the special terminal ends, and insulating boots from Rotax. plus a special pair of crimp pliers to install the terminals.

[okent]

Just went through this exact thing with my 2008 CTLS.  Had all the wiring checked and problem was still present.

Replaced the ignition modules and problem solved.

Interestingly, the plane now runs better.  I am getting a few more knots at the same fuel burn.

Don't ask me how.

The new one's come with the soft start.

[cdarza]

8 hours ago, Tom Baker said:

Replacing the "P" leads will be the easiest and cheapest thing to address first. The only problem is that you will need to order the special terminal ends, and insulating boots from Rotax. plus a special pair of crimp pliers to install the terminals.

Very much appreciate the quick response--Sorry, but just to clarify, as im not knowlegeable on this-   Are the "P" Lead the wire/s  the ones going into connector housing.  (as seen in the pic) and, are the insulating boots you refer to the ones that go into the module (very old looking the pic)?  Or am I on a different page?      Secondly,  if I go ahead and purchase the modules -need 2 of them correct and on the CPS site, they have 2 part numbers for the electronic module; Rotax 965-440 and 965-444.  are these essentially the same?     Ouch$2k  for both -- oh and yeah, this   on a 2006 CTSW (900hrs) so getting quite old. 

[Tom Baker]

"P" lead refers to the wire that runs from the ignition modules to the ignition switch in the airplane. You can trace them from the module around and through the intake manifold on the right side along with the rest of the wires on top of the engine. The rest of the ignition module wires stay with the engine.

[cdarza]

ok thanks -i  found a small problem with one of the wires from the modules however this was on the side that i didn't initially have a problem with - so i can't say this is the cause 

The ignition switch setup on my plane is switch 1 (first key click) goes to Module B and switch  2 goes to module A 

 

[cdarza]

"P" leads are the white wires 

[cdarza]

Feel as if i ripped out her heart lol

[Buckaroo]

Send that whole set up to Carmo in the Netherlands and they will rebuild the wires and check the modules. The turnaround time is 10 days and the cost to rebuild the modules is $500. 

[cdarza]

2 hours ago, Buckaroo said:

Send that whole set up to Carmo in the Netherlands and they will rebuild the wires and check the modules. The turnaround time is 10 days and the cost to rebuild the modules is $500. 

Thanks Buckaroo !!   and I'm glad you mentioned this as I'm  unaware of Carmo and initially I read CARMOL on your previous post ---   You can understand how weird that got.  LOL.    Btw is that $500 for the pair  or  for each module?

[Tom Baker]

For the pair. And for the record the 2 wires that you had to disconnect completely from the modules for removal were the "P" leads.

[procharger]

Use an inductive timing light to see if you are getting fire to the each plug stay away from prop. quick

check it works. Its what I do One other option take out plugs use some cable ties to ground

each plug to engine turn out lights have someone turn engine over and look for fire again stay away

from prop. make sure all are grounded if you go that way.

https://www.aircraftspruce.com/catalog/topages/drrotech.php

I have one of these it works. pricey

[Buckaroo]

16 hours ago, cdarza said:

Thanks Buckaroo !!   and I'm glad you mentioned this as I'm  unaware of Carmo and initially I read CARMOL on your previous post ---   You can understand how weird that got.  LOL.    Btw is that $500 for the pair  or  for each module?

Yes both set with soft start and other improvements.

[Runtoeat]

Just had the same issue as other members have reported earlier in this thread.  Yesterday, while cruising at 5300 rpm in my 2006 CTSW, I noticed I was having intermittent 50 rpm tachometer drops.  Engine would run fine and then I could feel the plane slow slightly and see a 50 rpm dropout and then the rpms would come back to normal. Although I was thinking it might be a fuel issue I figured it wouldn't hurt to see if it might be electrical so I did a mag check while in this flight.  First went to switch position #2 and had 50 rpm drop.  Then back to "1&2" position and back to normal rpm.  Then went to switch #1 and got 50 rpm drop then back to "1&2" and back to normal rpm.  I did this twice with just the typical 50 rpm drop at each mag.  Later in the flight, after continuing to experience the intermittent 50 rpm drops, I decided to do the mag test a third time.  Went to position #2 and got the 50 rpm drop.  Back to "1&2" and then went to switch position #1.  BANG!  Complete engine shut down!  I quickly went back to position #2 and much to my extreme relief the engine came back to life because the prop was spinning at my speed of 115kts.  Figured I wouldn't be stupid enough to try that again so I limped back to my airport hoping my one good mag would remain working properly.  Today my mechanic and I did a thorough "P" lead wire  and ignition switch "wiggle test" and poked around with ohm meter to see if anything unusual.  No problems found in wiring or in the switch.  Hoping it would fix my problem, we installed the set of soft start modules I bought 5 years ago that have been kept on the shelf.  An engine run up and subsequent test flight after installing the new modules indicates that they fixed this problem.  And, not only fixed the problem but the plane does have a better response to throttle and seems to have more power than usual.  The important thing to know here is that our modules do not only have the well known and documented "fail to start" problem.  They also have a "high rpm failure to run" problem.  It is now documented by owners on our forum that modules have failed to work at high rpm.  Owners who have early CT's, especially 2006 or 2007 years, with original factory modules might expect to have ignition problems eventually.  Hopefully, when failure occurs, only one module will fail and one will remain working long enough to allow them to get back home.  Seems I read that the military replaces the modules every 700 hours on the rotax engines used in drone aircraft.  

[okent]

Nice write up.  I didn't try the mag check in the air but on the ground and noticed that if I did a quick key turn the engine would shut off but come right back when I switched back to both.

My failure happened right around 800 hours.