PMag Tach signal erratic

AltonD · #1 04-11-2016, 05:11 PM

New installation.
All is normal with RPM till I apply take-off power. I get >3000 RPM. Engine is definitely behaving normally as before the PMag install. After reaching cruise, the indication settles down with an occasional blip while actual engine rpm remains unchanged.
I am reading the signal through a AFS-5500 unit. Double checked the wiring and pin-outs. All good.
initial wiring, I ran two #20 wires to the AFS unit, signal and ground. Second attempt, I ran a shielded wire to the AFS unit. No difference. Tomorrow, I am going to swap to the right PMag to see if the issues follows.

Anybody else dealt with this issue? I will put a call into EMagAir tomorrow morning.

SmilingJack · #2 04-11-2016, 06:37 PM

I did a long time ago and it was the ground.

I cut off the "ring terminal" and crimped on a new one.

Seems the crimp on the original wasn't as good as it should have been.

coghlin · #3 04-12-2016, 06:20 AM

I had my rpm wondering up and down on a 3500. Both companies pointed finger at the other one, but in the end it was a problem with my AFS 3500, which they said they hadn't seen before.

AltonD · #4 04-12-2016, 07:45 AM

Could be Ric. I was having, occasionally, the same problem with the sensor that was on my Slick. I am going to double check my grounds and swap to the other PMag and see if the problem follows. That should surely tell the tale.

SHIPCHIEF · #5 04-12-2016, 12:17 PM

Yes, I get that too. I run a P-mag on the left & a Bendix 200 on the right.
I have a Flight Data Systems electronic tachometer
http://www.fdatasystems.com/t-30-tachometer/
After flying a while, it settles down and reads right.
I'm saving up to get an EMS so I've been putting up with it...I have a few inches of un-shielded wire from the "mag' switches to the T-30. I should recheck the ground of the shields and reconsider the filter resistors.