912is rpm drop

Marty,

I have seen some problems with the X1 & X2 connectors, and I would suspect that area over the ECU connectors which are more robust. If you end up with a bad socket on the wiring harness side of the X1 connector, it is possible to very carefully remove the socket at the crimp while preserving the wire length. That way you can just crimp on a new socket and push it back in the connector body. If that does not work, you end up having to cut off all the sockets and start over to keep all the wires the same length. Either way, you would need an extractor tool, a proper crimp tool, and the new sockets.  Also, the locking rings on these connector bodies are easy to break if you turn them too hard.  What breaks is just small tabs inside the ring that run in the threads, so you won't see the damage, but you can feel that it does not positively lock. If that happens, the connector can vibrate loose and cause problems. Fortunately, the lock ring is available separately from electronics distributors and easily replaced.  You cut off the old ring with end cutters and then snap on a new one in about 2 minutes. If you need it let me know and I will post the part number for the lock ring and sockets. 

Jeff,

I can not find in my manual any connections labeled X1 and X2. Are you talking about the round plugs on the bottom of the Fuse box?

if so, how do they come apart? is it a threaded locking nut, or a 90 degree turn to disengage?

Marty,

Yes, the connectors I'm referring to are the round ones on the bottom of the fuse box.  The Lane A (X1) connector is on the left when you are facing the fuse box.  The lock ring releases about 1 turn counterclockwise then you pull straight down on the connector body.  The lockring runs in a steep thread with a stop at the locking position which feels like a notch when latched. Only use your hands to turn these, using a tool with break the locking tab inside the ring.  There is some information about these in the wiring harness section, 76-50-00 page 8 of the 912iS MMH.  

Also, I think you might find the attached full wiring diagram helpful.  If you study it, you will see that all pins on all connectors are illustrated.  The X1, X2, and X3 connectors are shown along the left side of the fuse box diagram.  I keep a poster size print out of this drawing on the wall in my hanger.  

Fedrick,

Sorry you are having the same issue.  Please let us know if you find anything!

Hi,

I went to the airport today and did a lot of measurements.

Cleaned the X1 and X2 connectors with contact cleaner and measured from the 10A fuses that there was continuity to the supply side of all 4 coils. Disconnected all spark plugs and measured the secondary side of all the coils, and they all measured the same value.

We went a step further and disconnected the ECU B-connector. Measured continuity to the signal side of coil 2 and coil 4. All ok there too. 

Did another testrun, and the fault is still the same.
Attached is our log-file extracted after the testrun.

Any ideas on how to proceed?

Fredrik,

I got a little confused because I just realized you are not the original poster. I see earlier you said you were having the same problem as Marty, but were the same cylinders and lane involved?  The advice I was giving was for Marty specifically, though it may also apply to you if your symptoms are EXACTLY the same.  You mentioned you inspected the B connector on the ECU, which would not apply if you were getting a Lane A fault (like Marty).  Please provide details of your specific problem.

The only fault in your log is related to the generators: "Generator Select in Fail safe". This is common and generally means that at the time the fault was logged generator B was still powering the engine functions because alternator A had not yet been verified. I would think this happened right after the engine was started and would have nothing to do with your RPM drop during a lane test.