Erratic RPM reading

[10ixwwybk2]

On high power settings, 2400rpm and above, the rpm reading on my Skyview is rapidly spiking upwards to 3000+ RPM.
The sensor wires are connected to the left and right P-leads at the ignition switch.
I have isolated the fault to the left mag. by switching mags.
I have also proved that the fault is not from the ignition switch to the Skyview by switching the sensor wires at the ignition switch.
Can anyone suggest what sort of fault might cause this.
This is on an a Continental 0320.
Thanks,
Robin

 

[jakej]

Robin
You need to change attitude from to this . Most of us are here to help a fellow aviator

What size resistors did you use in the rpm wires ?

Jake J

 

[10ixwwybk2]

Hi Jake,
You are right to admonish me, we are lucky to have problems like this.
I am using 30 ohm resistors.
Robin

 

[jakej]

Robin

You're correct, the small problems we shouldn't stress about - as long as it doesn't stop us from flying ;D

I'd increase the resistor value in say 20 kohm increments on the left mag & I think you can go to ~ 150 ? however I've never had to change from 30 kohm for any Slicks on 4 cylinder engine yet - you may need to get a more thorough check of yours if you can't 'fix' the high rpm reading issue.
Your mag switch can't be the cause of what you're seeing.
BTW are they new Slicks ?

Jake J

 

[Dynon]

And just to be clear, you're after you 30K Ohm resistors (that means 30,000 Ohm), not 30 Ohm. As Jake said, sometimes you need to up the resistance higher than 30K though. Folks have gone as high as 150K. You'll need to experiement to find the right value for your aircraft - if you go too high you'll see problems on the low end. Jake's advice of adding resistance incrementally works.

 

[10ixwwybk2]

Good advice thank you.
I put 60k ohms in each line and it now works perfectly.
Robin

 

[jakej]

Glad to hear & thanks for the feedback

Jake J