Hobbs meter runs when engine is not (EMS-120)

[aglock]

Hi!

I have noticed on occasion that the hobbs meter sometimes has lapsed a few decimals of an hour when beginning a new flight. Today made a test with master switch on and ignition on first step and the hobbs was ticking. It seems to me that this is wrong, the hobbs should only be ticking when the enginge is running and oil pressure is above a certain value, shouldn't it?

Is this a known issue or a wiring problem or pherhaps a configuration issue?
The aircraft is a WT-9 Dynamic with a Rotax 912-ULS with EMS-120 and EFIS D-100 and version 5.0 software.

Thanks!
//Andreas

 

[dynonsupport]

It should run when oil pressure is >15 PSI or tach is not zero. It should not run all the time. We'll have to look into this and see if we can find any bugs. I assume your oil pressure is near zero and your tach is at zero?

 

[aglock]

With tach, do you mean engine rpm or tacho time?
If you mean rpm the answer is yes. The EMS configuration is not set to Rotax but to other.

 

[aglock]

Ok, I have som more info and it is a little bit embarrassing. By some reason were we focused on the hobbs meter that we did not recognize that the oilpressure never goes down to 0. It hovers around 2.3 bars and shows about 2.7 bars when the engine is running which should be about right. The engine is a Rotax 912UL(s) manufactured in May 2008. We have tried to see which type of oilpressure sensor it is but it has no part number visible. It only has one wire from it though. Currently we have the oilpressure sensor set to 1 in the EMS-120 and have tried 2,3,4 also without success. Which rules out 4... where it showed 0 pressure even if the engine was running.

Any ideas?

Thanks,
Andreas

 

[dynonsupport]

It sounds like you might need a new sensor. We don't provide the oil pressure sensor that comes with the Rotax engines, though our normal oil pressure sensor is the same as the old Rotax one. Check and see if you can have yours replaced under warranty.

Once you get to the sensor, you can measure the resistance between the terminal and the case. At 0 psi, it should measure about 9.5 Ohms or less.

 

[PhantomPholly]

Can't stress this last one enough. I banged my head for over a month thinking "my ground was fine." Once I put in a whole new ground strap from the avionics bus to the engine, all sensor reading problems disappeared.