ECU Faults

RW,

Do you know what Half Sync refers to, or do you think I’m essentially right except for the speculation that this message is an artifact.  It must refer to the fact that only the Crankshaft sensor is synchronized.  Maybe it’s an acknowledgement that the ECU does not know if the cylinders are in a compression stroke or exhaust stroke.  In other words, Half Sync is the normal mode of operation.   

Jeff

Yes I would agree with your assessment of the loss of knowing where the crankshaft sensor count would be.  This is generally related to low voltage at the 5V sensor so it skips a few pulses.  Generally this occurs in startup of the engine where there has been heavy draw on the supply side.  This is why normally a reset seems to drop the problem.  There however may be an issue with draw internally in the ECU that can only be found with a diagnostic view on the log viewer program.  

Incidentally that program will be offered for people very soon starting in 2025 and persons with interest will be able to take a few days training and then they can get copy of the diagnostic log viewer.  The caveat from Rotax is that the training be completed before they will allow the use of the viewer.  It is not at all an insightful and intuitive program so requires a good understanding of the whole system to use.  

Incidentally from the perspective of the ECU just for your information the controllers had to meet full certification FADAC standards of the FAA.  The test levels are spelled out in   AC No: 21-16G  Note that the controllers have to undergo testing to RTCA D)-160, whatever the called out level is.  (may be C or D level)  This includes showing the requirement for testing for irradiated HIRF operations.  This is the same standards as any FAA part 33 engines or even airliners must have.  Rotax builds the ASTM and F33 (certified) version engines to the same standards for safety.  

Contact Motive and talk to them if you are interested in the training to use the log viewer.  I expect it will be in the next 4 to 6 months.

Cheers

RW,

I did not think “Half Sync” indicated a fault, I thought it was the state of normal operation. In other words, because there is no camshaft sensor, the ECU never knows if a piston is on a compression stroke or exhaust stroke, but it’s not important because the spark fires either way (wasted spark method). It’s my belief this is referred to as half sync, and is the normal mode of operation for the Rotax injected engine. Good to hear there will be a log viewer class.  If the full meaning of the codes are covered, it would be worth while.  

Jeff good question.  I have never seen a "half sync" so perhaps it is the way the instrument is selecting what to display.  

The ECU when it goes into startup looks at the flywheel via the CPS pickups.  ( at 200 hertz) and within 2 full revolutions of the crank will determine the correct stroke each cylinder is on.  I will ask a few people who know far more than i what they believe a "half sync" would be.  

Cheers

RW

“at the flywheel via the CPS pickups.  ( at 200 hertz) and within 2 full revolutions of the crank will determine the correct stroke each cylinder is on”

I don’t think this is accurate. The camshaft turns at half the speed of the crankshaft. So the crank makes 720 degrees of rotation for each camshaft revolution.  Most automotive engines have a camshaft position sensor in addition to the crankshaft position sensor to determine the stroke. The Rotax has only crankshaft sensors, so as far as I can tell the ECU has no way of determining position in a 720 degree cycle when it only sees the position of a 360 cycle. In other words, it does not know if a cylinder is on compression or exhaust.

The spark timing does not care, since it fires on both compression exhaust. I also suspect the fuel injectors fire at both the exhaust and compression strokes. This is known as “batched multi-point fuel injection” (as opposed to sequential) and works well for engines run at higher RPM. I believe this method of engine management is referred to as “Half Sync”, but it would be great to have a Rotax engineer validate these assumptions.  I realize this conversation is purely academic at his point, but this is worthy of understanding.