Upper spark plug during start

Marco,

It’s almost impossible for all the lower plugs to be firing and all the upper plugs not firing.  Each dual ignition coil fires one top plug on a cylinder, and a bottom plug on another at the same time.  So you would need to have four faulty ignition coils or four faulty wires for the complete top or bottom bank to be out. Like I said, almost impossible.  

Each time a coil fires, one of the sparks happens in a cylinder in compression, the other in a cylinder in the exhaust stroke, so that spark is wasted at the cylinder in exhaust stroke. With both lanes operating you should see the top and bottom plug fire at (almost) the same time.  However, if you only had one lane active, you would not see both upper and lower plugs firing at the same time on a given cylinder.  As an example, when coil pack SP-1 fires, you would see the bottom plug on cylinder 1 fire, and the top plug of cylinder 2 at the same time. The other plug on each cylinder would fire, but on a different revolution of the engine.  

Section 74-00-00 of the 912iS Heavy Maintenance Manual has a good system description and also a distribution diagram of the ignition coils and plug wires.  Also, check out this post for more details. Note that this post is not about the 912iS specifically, but the principles are similar in that both engines utilize four dual ignition coils and the wasted spark design.  

https://www.rotax-owner.com/en/912-914-technical-questions/7987-when-exactly-do-the-spark-plugs-fire-in-the-912uls?start=0

If the engine was stored for three years, the most likely problem is clogged injectors, which you stated that you have already found. Others have reported this problem after storage of a new engine.  The next step would be to clean all the injectors.  

You can’t be clever at diagnosis without BUDS but you can have an easy try switching injector from an other cylinder.And remember the it’s not aloud to test ignition with plug at the external that’s the best way to damage the coils ant the ECU …

Kristof

The Rotx fuel-injected engines a notorious for getting the maiden first start happening.
The engine starts on the B Lane Only.
Once the engine reaches 2500 for 5 seconds; the A lane is enabled.
The first start may take 10-20 tries until it continues to Run.
At first, you get a few intermittent firings and then it stops.
Eventually, it will run rough for a few seconds before it stops.
Then it will idle OK on the B lane alone until the A lane is enabled; Then it stops.
After all that, it will idle smoothly for 5-10 seconds and then get rough and stop.
Finally, it will start, idle, rev up, and run smoothly.
Be patient, and just keep trying.
It takes a while for all the air and stale factory fuel to be flushed from the Injectors.
Way longer than you might expect.

Grazie Bill, 

You are very helpfull.

I had a call with two official rotax mech and one engineer , nobody were aware that only one line is active during start procedure and for them was an installation/electrical issue.......

Grazie

MArco