"B" ignition dead?

[E. D. Eliot]

Third short run on my 912 ULS today. We did not check the ignitions during the first runs as it started either hot or cold on the second or third blade every time and is a strong runner at all engine speeds. Idle is beautiful. This engine was purchased from Van's six years ago. We have found that with the engine running at all speeds when the "A" is shut off, the engine stops immediately. Troubleshooting suggestions please. Thanks.

 

[bbaggerman]

Take a look at the troubleshooting section in the Rotax Heavy Maintenance Manual section 74-00-00.

There are two pairs of ignition connectors near the ignition modules on top of the engine. One pair (Ignition A and Ignition B) is from the charging and trigger coils on the back of the engine to the electronics ignition modules. The second pair of connectors is from the electronic ignition modules to the four ignition coils. On a 912 engine troubleshooting ignition problems usually starts with swapping the first pair of connectors and see if the problem moves. Then swapping the second pair and see if the problem moves. That narrows the problem down to charging and trigger coils, electronic modules, or coils.

When you do the connector swap be sure to write down your connector configuration and test results. You think you will remember but you won't!

 

[Tony Kirk]

912 ULS Ignition Problems

Lockwood Aviation made a nice video describing how to go about performing this type of Ignition system troubleshooting.

https://www.youtube.com/watch?v=Wi4v27UG-2Q

 

[bobg56]

When helping a friend install his engine I didn't skin back the wire shielding and crimped the connectors onto it and inserted them in the ignition canon plugs, these were leads that come off the shut off switches there by causing them to be grounded (off). we couldn't start the engine due to no spark. I forgot that these leads have shielding that need to be peeled back an inch or two first.

 

[DHeal]

On my RV-12 / 912ULS one of the ignition switches was occasionally failing to the "Mag ON" position. It was easy to replace the errant switch with a new one from Van's.

 

[E. D. Eliot]

Thank you all for the replies

Thank you all for the very helpful replies. We continued our search for a loose wire connection yesterday. Found that the wire shielding on J-173 was pretty roughed up and compromised. This shielding did not have continuity with ground no matter how we reinserted it into the ground bundle. The wire underneath the shielding is electronically good. Did not have time to do further testing or run the engine. Called Rotax Dealer in Wisconsin and they were extremely nice and want a picture of the wire which I will send. Called Van's and they too want a picture of wire number J-173. They have no such number in their parts inventory. Van's was extremely helpful, will do further research and call me back. More to follow = thank you all again who responded - I appreciate.

 

[Piper J3]

Leading Edge Airfoils in Wisconsin will sometimes sell used serviceable parts.

Worth asking....

 

[MMiller]

… Found that the wire shielding on J-173 was pretty roughed up and compromised. This shielding did not have continuity with ground no matter how we reinserted it...

I think you mean wire J153. This is one of two conductors in a shielded pair within a wire harness the KIA identifies as “WH-RV12-IGNITION”. The J153 conductor connects the the disable pin of the A ignition module to plug on the Rotax harness.

I’m not sure where you are taking measurements. The grounding of this harness is relatively straightforward. A small section of the insulating jacket is removed from an intermediate point of the cable exposing the shield and it’s clamped to ground with all the other braided cables. At the ends of the harness the shields are not accessible since they are enclosed in heatshrink and don’t terminate to pins. The ground in this 19-inch cable is for RFI noise reduction, it has no effect on engine operation…unless it’s shorted to an inner conductor.

 

[bbaggerman]

I never have been wild about how these shielded P leads are tightly clamped with a metal clamp. It is a nice convenient way to terminate the shielding but with just a little vibration the edge of that metal clamp could work its way through the insulation and short the P lead to ground. Heck, that’s what could be going on here.