I recently had an in-flight stoppage on my Hirth F 23 fuel, injected engine.
The engine has dual CDI ignition with a signal lead from each CDI control module that provides a tachometer signal. That signal wire also goes to the ECU to provide information for the fuel injection.
The wiring instructions have you tee the tach signal wires from the two CDI modules together, to provide redundancy to the signal to the ECU in case one CDI module fails. Without a tach signal, the ECU won’t provide fuel to the engine.
However, if a CDI module fails and grounds internally, it can fail the tach signal from the good CDI module (because they are teed together). The engine stops because it’s not getting a tach signal to the ECU, even though it’s got a functioning, single ignition. If the engine was carbureted, it would continue to run and the ignition failure would be caught at the next run up.
Reportedly, it’s “rare”, but I don’t want to continue with the same wiring and the same potential failure mode since I’ve already experienced it once.
One solution would seem to be a switch to select the tach source, but that adds additional complexity and failure points, and another item to deal with an emergency situations where the last thing you want is another item to deal with. It’s a pretty crude solution that I would prefer to avoid. Plus, I literally have no panel space even for a switch.
Has anyone else encountered this issue?
And, has anyone implemented a system to avoid this failure?
Wiring diagram, and Hiirth troubleshooting guide attached. It makes me wonder how “rare” the problem is when it’s described in a troubleshooting sheet.)
The engine has dual CDI ignition with a signal lead from each CDI control module that provides a tachometer signal. That signal wire also goes to the ECU to provide information for the fuel injection.
The wiring instructions have you tee the tach signal wires from the two CDI modules together, to provide redundancy to the signal to the ECU in case one CDI module fails. Without a tach signal, the ECU won’t provide fuel to the engine.
However, if a CDI module fails and grounds internally, it can fail the tach signal from the good CDI module (because they are teed together). The engine stops because it’s not getting a tach signal to the ECU, even though it’s got a functioning, single ignition. If the engine was carbureted, it would continue to run and the ignition failure would be caught at the next run up.
Reportedly, it’s “rare”, but I don’t want to continue with the same wiring and the same potential failure mode since I’ve already experienced it once.
One solution would seem to be a switch to select the tach source, but that adds additional complexity and failure points, and another item to deal with an emergency situations where the last thing you want is another item to deal with. It’s a pretty crude solution that I would prefer to avoid. Plus, I literally have no panel space even for a switch.
Has anyone else encountered this issue?
And, has anyone implemented a system to avoid this failure?
Wiring diagram, and Hiirth troubleshooting guide attached. It makes me wonder how “rare” the problem is when it’s described in a troubleshooting sheet.)
