RPM Speed Warning in the Cruise

[AlanR]

Hi,
Suggestions and thoughts on this problem please..
Bristell NG5. Classic D1000's x 2. Rotax 912uls engine with CS Prop.
When flying today I got for a few moments whilst in the in the cruise a repeated 'Engine Speed' warning from the nice lady and could see the RPM gauge was fluctuating wildly between 2000- 6000 rpm although the engine sounded and felt just fine. I was cruising at the time at 4800 rpm with 24.5inches MAP so I momentarily played around with the throttle which was all I could think to do at the time. The problem went away immediately and I continued and did the remaining 30 minutes of the flight home without any further issue.
After landing I tried to replicate the fault at all power settings without success and everything seems all good.

The question I now have is...Do I now go delving into the back of the panel ( where the EMS is located = difficult ) looking for a wiring fault? Is the EMS maybe faulty? Alternatively do I do nothing and hope it was a one off glitch?

All thoughts appreciated on what would you do?

Alan

 

[Rhino]

Obviously there's no way of knowing for sure without checking, but in my experience problems such as this are far more likely to be caused by a sensor or sensor wiring, usually on the engine end. I'd check there first.

 

[AlanR]

Thanks for the thoughts.
I am pretty sure though there is no fault on the Rotax trigger coils where the rpm is picked up from or the wiring from the engine at all because the CS Prop controller also displays engine rpm ( from same engine feed wire)and that was perfectly stable at 4800 rpm during the Skyview display fluctations/warnings.

 

[sunfish]

Perhaps check the contacts in the ignition switch?

 

[AlanR]

Ok...Now uploaded the Data Log files which show that the high/Low RPM fluctations event shown on Skyview screen lasted 16seconds and although the engine rpm was actuallly perfectly ok and didn't actually fluctuate at all I was getting alerts and Indications of High/Low rpm on screen . It also shows two instances of EMS FAIL, one as SHOWN and one as HIDE, whatever that means.
Unsure where that leaves me in troubleshooting the problem but at least it proves that I didn't imagine it!

 

[Rhino]

Contact support.

 

[AlanR]

Further to this I put the data upload into Savvy and it showed an Oil Temp drop/spike for 3seconds of 60degrees F which can't happen in reality but it did however give me some sort of lead on where to look.
I couldn't see anything wrong with the oil temp sensor connection but I cut the terminal off and fitted a new terminal.
Since then I have done a total of 6hours flying and not had any re-ocurrence of the previous shown on Skyview big RPM fluctations and constant caution warnings.
So have I cured the problem?....and how does if it was the oil temp terminal and the spike shown have anything to do with the rpm?
Who knows?....I guess time will tell if the problem happens again!