Autoipilot is drunk - AeroCruse 100 wandering

[2seatpilot]

Starting a thread here to try and help my friend solve his AP issues. He has a CTSW that with the Bendix King AeroCruze 100 autopilot. Installed GPS is the AvMap EKP-IV, and it seems to be properly connected and talking to the AP.

Since he bought the plane, it has not functioned correctly. Avionics shop made a few corrections to the install which improved things slightly (at least now it engages...), but it still wanders all over the sky. Altitude hunting starts with small corrections that get bigger and more dramatic until you disengage, has trouble maintaining the track... even trying to fly it with just bank angle isn't consistent. 
Last flight with it after some more investigating and testing by the shop, we made a few adjustments to the settings (found on this forum) and it improved the lateral stability, though still has trouble finding the track, and vertical is still all over the place. Ground testing according to the manual all checks out fine. Flight test... it's a wild ride. 

We used the attached spreadsheet from Runtoeat's post http://ctflier.com/topic/737-trutrac-digiflight-ii-vs-porpoise/?do=findComment&comment=4820
trutrak ap settings_ctflier forum.xls

Unfortunately we were unable to achieve a satisfactory result, but now I'm not sure what to adjust in order to chase the desired effect short of random changes, which don't really help much. The main questions at this point... for EACH setting in the vertical and lateral setup, what is the actual action being controled by the setting? 

How can we definitively determine whether or not the unit itself has a problem, vs a setting problem? I'm beginning to wonder if the AHRS system is just not functioning correctly in the box - we've properly set the gyro on the ground (held for 1 min - ?is there supposed to be a message to indicate they are successfuly set?), synced the altitude prior to takeoff (though I'm not sure that  is staying synced - need to look closer at that, could be part of the issue)

So - sugguestions of what to try, what to look for, troubleshooting tips and possible solutions... open to all!!!

It's a nice weekend, hoping to get in the air and try to figure this out. 

[FlyingMonkey]

A lot of APs will wander or hunt if the gain is set too high.  I'd start there by turning gain down if there is a setting for that.

[Madhatter]

AP will hunt slow if gain is to low and hunt fast if too high. If there is any slack or looseness in the coupling to the servo it will also hunt just like loose bridal cables in other types of autopilots.

[2seatpilot]

well there is a GPSS gain... so that might have an effect on how well it follows the GPS track? 

For the others (Lat Activity and Microactivity, Vrt Activity and Microactivity) are these the same as "gain" settings in other autopilots? 

I believe the shop checked all the physical connections between the servos and the airplane, and I think they're good. 

 

[Anticept]

https://www.bendixking.com/content/dam/bendixking/en/documents/document-lists/downloads-and-manuals/TT-167-Vizion-PMA-Autopilot-Operating-Handbook.pdf

https://www.bendixking.com/content/dam/bendixking/en/documents/document-lists/downloads-and-manuals/TT-166-Vizion-PMA-Autopilot-Installation-Guide.pdf

This autopilot will require manual trim input. There should be vertical bars  that show up on the face of it indicating which trim direction the autopilot is requesting. If the pilot does not trim, it is harder for the unit to hold altitude. This is not a unit that adjusts trim itself.

Also, verify the pitot static system has no leaks.

In regards to roll: Make sure there's no slack in the cabling.

I can't find anything in there about adjusting gain, there might be those settings but you might have to call bendix king for support (trutrak is part of them now)

[Madhatter]

You will figure it out eventually.  I've fought lots of autopilots, Britain, Century, Cessna, S Tec,, even an L2, it just takes time and phone calls. So far the best was Garmin but you have to have a G3X.