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Date:  7-19-2017
Number of Hours:  2.00
Manual Reference:  
Brief Description:  Ignition Module Failure

While taxi testing, and with the engine thoroughly warmed up, and running on ignition #1 (electronic side,) the engine started running rough at low rpm, but ran smoothly when ignition #2 was turned on. This also happened during subsequent taxi tests.
After ruling out the wiring, fuses, and switches, I started the trouble shooting process by interchanging the two ignition sides at the input to the diode switcher, then the coils. In both cases, both sides ran perfectly when the engine was not heat soaked, but ignition #1 ran rough when heat soaked.
In this very simple ignition system, there was only one component left that was not common to both ignitions, the XR-I points replacement module. This is the only “active” electronic component in the system, so a more likely candidate for failure. Also, it was initially wired backwards due to a wiring error. After the wiring was corrected, everything ran correctly, so I thought I dodged a bullet.
After carefully mounting the module in exactly the same physical location, with a 0.0015” thick piece of Kapton tape serving as a spacer between the module and the distributer cam, everything was tightened up, the tape removed, and the cap installed.
After starting the engine, the rpm on ignition #1 was 50 rpm higher than the points side, indicating the module timing was ahead of the points side by a significant margin. The timing light indicated that ignition #1 was at 33 degrees while the points side was at 28 degrees, the desired setting. The ignition module was moved very slightly to correct the timing. Another taxi test was completed, and the engine allowed to fully heat soak. Fortunately, the roughness on ignition #1 was cured.
William Wynne had said that if power was applied to the module in reverse, the module was toast. Of course he was right. Even though it initially still appeared to work, I should have replaced it immediately. I sure am happy that I found the problem before test flying.
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New Ignition Module

New Ignition Module

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