Scott & Tanya Card RV9A build log (N4822C)

I double checked all of the ARINC 429 wiring from the EFIS to the A/P switch to the autopilot both electrically and physically. All of that wiring is just fine. Carlos at GRT said it seemed like I had some faulty wiring that was causing my intermittent autopilot GPS Steering disconnect. He hasn’t seen the care taken in my connections. I double checked anyway. I physically looked at and handled each connection, and put an ohm meter across each connection, and the full end-to-end and didn’t see any odd resistance. Also checked resistance with wiggling wire bundles. It is rock solid.
I haven’t been able to do enough flight testing to really nail down the conditions yet on this, but I’m starting to wonder if the internal GRT GPS unit is briefly loosing position lock. That would explain the A/P disconnect and also maybe the incorrect wind direction and speed indications. Although I don’t remember seeing any odd ground track indications, which I would think would be obvious. I’m just thinking out loud here. I’m pretty sure that these problems are only obvious when I’m using the GPS2, which is the internal EFIS GPS. I need to test and see if I can get a failure with the Garmin 430 driving the A/P through the EFIS.

Yesterday I went to the hangar to do some more diagnostics on the oil and carb temperature probes. All of my wiring is golden. They only go nuts during engine run vibration, so I decided to induce just a bit of vibration (wiggle the wire a little bit) right were the wires enter the probes. Sure enough, when I wiggle the wires right at the probe, the instrument reading freaks out. This occurs on both the oil temp and carb temp senders! Wow.
So I called GRT and talked to Sandy and told her my sad story. She commented that these temperature probes start out with the same sender units that are just potted into different probe assemblies, so she was very interested that they both failed in the same way. They are replacing them both at no cost. Whew, now I can move on to other stuff. I like progress.

I heard back from Brad today. They ran may failed P-mag for over an hour and it ran fine. It had not exceeded their temperature specification (which he said is the same as a mag, whatever that is). The only weird thing that they noticed is that the run time counter only turned on at operating speeds and showed only a few minutes of run time. They replaced the electronics board and are sending it back to me. So far as I can tell, the only difference between when I removed it (failed) from the aircraft and shipped it back and them testing it today (not failed) was temperature. When I took it off, it was still warm, but not so hot that I couldn’t handle it. He assured me that they would do whatever they could to keep me happy, including offering to send another e-mag to have on the shelf while they were at Oshkosh just in case that would make me feel better. I declined the standby unit.
This is definitely not the kind of failure that you would want to have. I’ll keep flight testing it and hopefully it is worked out.

The switch-out of the connectors on the oil and carb temp probes didn’t fully solve their periodic wacky readings. The only other parts of the equation are the pins at the EIS connector and the probes themselves. I’ll open up the EIS connector to take a look sometime soon. Then I’ll order new probes to see if that helps.

I talked to Brad at e-mag this morning about my failed P-mag. Most of his interest was focused around high temperature. He noted that they do record the highest temp that the ignition has seen, which is good for temperature related failure analysis. He should have the unit tomorrow morning and I should have it back Wednesday. I didn’t ask him to ship me another unit if he could get it turned around the same day. Otherwise I will ask for him to ship me something.