FredG Posted September 8, 2023 Report Share Posted September 8, 2023 912 ULS with 400 hours runs rough at about 3000 rpm. During mag checks, the roughness is fairly pronounced on one ignition and not on the other (runs on either one). The rough side has a 200 rpm drop and the non-rough side has a 100 rpm drop. This persists at 3500 rpm and other values, as well. When the six-pin plugs from the trigger coils to the ignition modules are swapped (B trigger coils to A module and A trigger coils to B module), the roughness changes side (ie, the single ignition switch position that was rough became smooth and the formerly smooth side becomes rough). Given the above, it should be no surprise that swapping the six-pin plugs from the ignition modules to the ignition (high voltage) coils also changed the side of the roughness. Replacing the four trigger coils made no difference. Rebuilding the carburetors made no difference. The resistance tests of the ignition coils were within specification. All eight spark plugs were replaced, no difference. The resistance of the spark plug caps were tested, all were 5K ohms. Any suggestions? Thanks, Fred Quote Link to comment Share on other sites More sharing options...
Madhatter Posted September 8, 2023 Report Share Posted September 8, 2023 How about bad module Quote Link to comment Share on other sites More sharing options...
FredG Posted September 8, 2023 Author Report Share Posted September 8, 2023 Forgot to mention. Both modules replaced with new modules. No change. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted September 8, 2023 Report Share Posted September 8, 2023 Still sounds like bad module. When you swap A & B and it follows, it seems pretty definitive. Also I am assuming you made any required wiring change that may be required as I had to on my SW for the new modules. Quote Link to comment Share on other sites More sharing options...
Anticept Posted September 8, 2023 Report Share Posted September 8, 2023 Well, if you swapped A&B and it jumped, and swapped the INPUTS to the modules and it jumped again,the issue's further upstream. Maybe an issue with the magnetic pickups for crankshaft position sensing? Might need the gap adjusted. Maybe a bad ignition energizing coil? Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted September 8, 2023 Report Share Posted September 8, 2023 Sounds like a trigger coil issue on the back of the engine. It may just need the gaps adjusted and it's possible it's a bad trigger coil. You did several trouble shooting thi gs. But some of those wouldn't have been the issue. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted September 8, 2023 Report Share Posted September 8, 2023 I thought you had checked all coils Quote Link to comment Share on other sites More sharing options...
Anticept Posted September 8, 2023 Report Share Posted September 8, 2023 To be fair I also had a bit of trouble following what he said he tried Which isn't hard since I speedread things on this forum. Quote Link to comment Share on other sites More sharing options...
Skunkworks85 Posted September 8, 2023 Report Share Posted September 8, 2023 You could have a "leak" in one of your ignition cables. If it was shorting out, you may have a random misfire on one coil. Quote Link to comment Share on other sites More sharing options...
FredG Posted September 8, 2023 Author Report Share Posted September 8, 2023 Synopsis: Replaced both ignition units with new boxes ( A and B ), no improvement Swapped the 6-pin plugs from the trigger coils to the ignition boxes (before and after replacing the ignition boxes with new units), the problem changed sides but didn't get better Replaced the four trigger coils and set the gap, no no improvement Rebuilt the carbs, no improvement Replaced the spark plugs, no improvement Checked the resistance of all eight plug boots, all good Corey - ignition energizer coil is a possibility, thanks Skunkworks - agree, ignition coils and ignition (plug) wires are still suspects Thanks all for your input. Quote Link to comment Share on other sites More sharing options...
Gabriel Posted September 10, 2023 Report Share Posted September 10, 2023 We have exactly tha same problem with 912ULS engine: Testing ohms (not replacing) the four trigger coils , all are ok. Rebuilding the carburetors made no difference. The resistance tests of the ignition coils were within specification. All eight spark plugs were replaced, no difference (by single electrode NGK). The resistance of the spark plug caps were tested, all were 5K ohms aprox. The resistance of the HV coils were tested, all ok, aprox 6K. Modules A/B replaced by another different modiles. HV coils replaced too. Trigger coils on the back of the engine, gaps adjusted. Important: mag switch wire is on six pins trigger coils connector, if the problem is triggers coils, changing this connector the problem stays im the same side. I think this is valid for energizer coil too. We hace changed HV wires too. Any more ideas? Thanks Quote Link to comment Share on other sites More sharing options...
Madhatter Posted September 10, 2023 Report Share Posted September 10, 2023 Sorry to here this, I know it's frustrating. I've had issues like this in the past especially in avionics and some propellers. I don't doubt that you will eventually find it. Without having the engine it's hard to analyze anything. Maybe isolate each side completely and eliminate any chance of crossover interaction in wiring. Don't give up, you will find it. Then let us know so we don't have go thru sleepless nights like you will Quote Link to comment Share on other sites More sharing options...
Jim Meade Posted September 10, 2023 Report Share Posted September 10, 2023 Brett Lawton says multimeter ohms tests don't use voltage levels that are typical of those found in the ignition circuit. Quote Link to comment Share on other sites More sharing options...
FredG Posted September 10, 2023 Author Report Share Posted September 10, 2023 Gabriel, you make an important point regarding the fact that the mag switch lead ("p"-lead or kill lead) is on the connector from the trigger coils. If the plugs from the trigger coils are switched, the problem will change sides for that reason alone, no matter where it is. I was told to keep the mag switch lead connected to its original ignition module when switching leads from the trigger coils to the ignition modules. Quote Link to comment Share on other sites More sharing options...
Gabriel Posted September 10, 2023 Report Share Posted September 10, 2023 2 hours ago, Jim Meade said: Brett Lawton says multimeter ohms tests don't use voltage levels that are typical of those found in the ignition circuit. Of course, I know that low DC voltage that multimeter uses is very different to dynamic conditions of voltage pulses at 4000 rpm or high spark plug voltages. Quote Link to comment Share on other sites More sharing options...
Gabriel Posted September 10, 2023 Report Share Posted September 10, 2023 50 minutes ago, FredG said: Gabriel, you make an important point regarding the fact that the mag switch lead ("p"-lead or kill lead) is on the connector from the trigger coils. If the plugs from the trigger coils are switched, the problem will change sides for that reason alone, no matter where it is. I was told to keep the mag switch lead connected to its original ignition module when switching leads from the trigger coils to the ignition modules. You don't need to do that, change the "P" lead. I describe my case: Module A is connected inside my plane to right mag switch and Module B is connected to left mag switch. 1st step: Setting OFF right switch (grounding P lead) I'm "stopping" Module A : Problems appear, I am turning off the module/branch in good condition. Both ON again... Setting OFF left switch (grounding P lead) I'm "stopping" Module B : There are not problems, I am turning off the module/branch in bad condition. With this, I can assume that the problem is in anywhere on system connected to Module B (from trigger coils to sparkplug) Flip horizontal connectors: When I flip horizontal connectors from Modules A / B I'm changing trigger coils and P leads. Remember that problems were in branch (all systems) connected to Module B (first step) If problems now are setting OFF left switch (left is now connected to Module A that is OK ) is because trigger coil from branch B are OK. I'm turning OFF the good branch. If problems are still setting OFF right switch (now is on Module A that is OK) problems are on trigger coils because the bad branch is now Module A (but Module A y HV branch A was fine in first step ). I needed a drawing to imagine it better, editing it with 'paint' Regards Quote Link to comment Share on other sites More sharing options...
Anticept Posted September 10, 2023 Report Share Posted September 10, 2023 https://www.lucidchart.com/pages/ Quote Link to comment Share on other sites More sharing options...
Gabriel Posted September 10, 2023 Report Share Posted September 10, 2023 22 minutes ago, Anticept said: https://www.lucidchart.com/pages/ Thanks Quote Link to comment Share on other sites More sharing options...
FredG Posted September 10, 2023 Author Report Share Posted September 10, 2023 Gabriel, yes, it is possible to keep track of the ignition being tested while keeping the p-lead in its original six-pin connector. I find it easier to test by moving the p-lead from connector to connector so that it stays with its original module. Both approaches work. Quote Link to comment Share on other sites More sharing options...
Jim Meade Posted September 11, 2023 Report Share Posted September 11, 2023 21 hours ago, Gabriel said: Of course, I know that low DC voltage that multimeter uses is very different to dynamic conditions of voltage pulses at 4000 rpm or high spark plug voltages. So you know that you can't inevitably trust the ohmeter. That was my point. Quote Link to comment Share on other sites More sharing options...
Anticept Posted September 11, 2023 Report Share Posted September 11, 2023 Fred, idea. I assume you have yellow tagged modules now? Warm up the engine, then disconnect the soft start leads and go out and do the run up. Quote Link to comment Share on other sites More sharing options...
procharger Posted September 11, 2023 Report Share Posted September 11, 2023 I had some engine running problems a while back replaced ignition switch seems to be the only thing that fixed it. Did all the checks didn't find anything wrong. My switch was sloppy and worn out. When turning the key there wasn't much resistance between positions new switch was three times harder to turn than the old one. Quote Link to comment Share on other sites More sharing options...
procharger Posted September 11, 2023 Report Share Posted September 11, 2023 I also have a doctor rotech that checks all the coils trigger coils and modules. Quote Link to comment Share on other sites More sharing options...
procharger Posted September 11, 2023 Report Share Posted September 11, 2023 Dr. RoTech Engine Diagnostic Tool By Mary Bernard - February 2, 2012 0 Light Sport Group has announced the introduction of its Dr. RoTech engine electronics analyzer for Rotax 912 and 914 series engines. Dr. RoTech was designed to assist aircraft mechanics, pilots and aircraft owners in troubleshooting the systems of the most popular line of Rotax engines. It will provide initial and preliminary troubleshooting information on all the major electrical system components described in the 912 powertrain maintenance manual when it is plugged into the six-pin plug on the Rotax ignition system, according to Light Sport Group. Troubleshooting electrical problems on the 912 series of engines previously required the use of a voltmeter and extensive knowledge of the aircraft’s electrical system. Dr. RoTech can plug directly into the ignition module’s connector or can detect which system you are testing if using the test lead/probe. Labeled green and red pass/fail lights indicate which systems are functioning properly. Dr. RoTech performs all of the required measurements of BRP-Rotax 912/914 Heavy Maintenance Manual section 74 paragraph 3.12, the company says, which include: the generator coil (on stator), charging coil (on stator), trigger coil (A&B), primary ignition coil (A&B), secondary ignition coil, spark plug connector, ignition switch and engine ground. Dr. RoTech also offers PC support, allowing users to plug into a computer to obtain more specific information such as a failure counter for troubleshooting intermittent problems. The price is $499.99. For more information, visit www.lightsportgroup.com/rotech.html. Quote Link to comment Share on other sites More sharing options...
FredG Posted September 11, 2023 Author Report Share Posted September 11, 2023 Corey, thanks for the suggestion. Procharger, thanks for your input. Yes, a faulty ignition switch can cause these problems. To test for that, the p-leads were disconnected from the six-pin connectors and temporary pins with ground wires installed. The problem persisted even after the ignition switch circuit was removed from operation in this way. The Dr. RoTech seems like a useful tool. It will not, unfortunately, identify ignition coil or ignition wire faults. Quote Link to comment Share on other sites More sharing options...
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