Erratic RPMs on AFS-2500

I had my prop overhauled this week and the prop shop had to charge the battery after the master was left on for a day or so. I picked up the plane today and found my engine monitor was reporting my RPM WAY to high. When I was at idle, 800 rpm or so, it would display 1600 to 1800. When I powered to 2500 rpm (verified by prop balancing equipment) it would show greater than 2700 and sometimes as high as 3000. As I made a short 30 minute flight the RPMs displayed would keep rising...about 10 per second. By the end of the flight I was over 15,000 RPM.

I called AFS and they thought it might need to be reset to factory defaults and then enter my personal settings. I haven't tried this yet but I hope they are correct. I figured I would post this here and see if anyone else has encountered a similar issue.

Sensor failure

Had the same problem. It turned out the glue or epoxy on the sensor pick-up had failed. Re-glued the sensor, problem solved. Advanced might remember that, as I informed Rob during my discovery. Hope it is that easy for you.

Doug

I had this problem. Mine was due to the pickup connectors flopping around in the breeze under the cowl. I put a few more wire ties on the connectors and problem solved.

Hi, Tony

You might also check that the ground strap to the engine is good.
Although if this is a problem a lot of other reading would be having problems.

Kent

loose sensor

A friend just went through this same problem. He purchased a new sensor. When he went to install the new sensor, he put a wrench on the old sensor to remove it and discovered that it was loose. He tightened the old sensor and test ran the engine...problem solved. The factory was nice enough to refund his money on the un-needed new sensor.

Now if we could just figure out how to make the 2500 stop leaking enough RF to jam GPS we'd be thrilled.

I will be checking things sometime tomorrow afternoon. Too busy today. Thanks for all the suggestions. I am doubtful though because it worked perfectly when i dropped it at the prop shop and after the dead battery incident, and the prop shop charging the battery while in the plane, I am thinking it is not a loose sensor but I suppose it is possible. I haven't even located the sensor yet....I have dual PMAGS so I assume it is connected to one of them in plane sight.

I'll be checking that sensor and wire connections today but I came across something in the manual, http://advanced-flight-systems.com/Support/AF-2500support/AF-2500%20System%20Manual%20V3_2.pdf, the calibration of the tach transducer (RPMs) state it should be set for 4 pulses for electronic ignition. When I spoke to AFS on the phone they stated it should be 2 (but Trevor was working off the top of his head). So if it is actually supposed to be 4 instead of the 2 it was set at....could this be my issue? Am I right in assuming my PMAGS should be set at 4 according to the manual?

PMags should be set to 2 pulses / rev.

If you have two PMags you are not using our RPM sensor?

If you have one PMags and one Mag you could be using the PMag or our RPM sensor?

If you are using the PMag RPM sensor you need to make sure that your analog module is setup for a 12V electronic signal. If you connected the 12V PMag signal to our standard RPM sensor input it is not going to work and might have damaged it.

Rob Hickman
Advanced Flight Systems Inc.

Thanks for trying Rob. Your involvement on this forum and others is part of the reason I love your products and if I go glass...it will more than likely be AFS.

I took AFS's advice and wrote down all my settings before resetting the engine monitor back to the default settings. I reset the settings and then went to re-enter my own settings. Come to find out I didn't have to change anything. Perhaps running the battery to near 3 volts reset the unit on it's own and my previous settings had already been erased.

So I start the engine to see if my RPM display would work. No dice. It still displayed erroneous values. Just for kicks I went back into the settings and set my pulse rate to 4 instead of the 2 suggested by Rob and Trevor. Yep, it WORKED! I am very happy to announce it works perfectly now.

I am not sure why Rob and Trevor say it should be set at 2 pulses... Perhaps they overlooked my particular set-up. Dual Pmags. I searched for a loose connection but found none. I also read through the Pmag manual and the tach signal comes from the "6th port". I inspected my set-up and discovered 1 lead coming from the 6th port from the right Pmag only. I didn't find any sensor so I am not sure if I have one.

Either way, I know my particular set-up calls for 4 pulses instead of the normal 2. Somewhat confused but happy it's fixed.

That is interesting indeed! The number of pulses per revolution is set by Pmag, not the EFIS/EMS display. All of the ones we have seen have been 2/rev. Good to know that fixed it!

Do you have one of our RPM boards or is your Pmag tach output wired directly to the RPM input on the AF-2500 analog module?

I didn't see any sort of board or sensor, at least not FWF, so at this point I assume it is just a direct wire.

The only reason I tried 4 pulses is because the manual says 4 pulses for electronic ignition. Could it be that my unit is so old that the protocol has changed?