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"mag drop" Troubleshooting

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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

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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.

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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.

 

 

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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

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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.

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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.

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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!!

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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

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