L ENG ECU FAIL during runup...

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UTMark
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L ENG ECU FAIL during runup...

Post by UTMark »

We have what seems to be a developing problem on N100DA.

2 Flights ago when preparing to depart Sedona, AZ, we went through our normal run-up procedures. During the L ENG ECU test, we had an unusual failure we'd never seen before.

1st Occurrence, 11/30/2021 (plane sat for 3-4 hours after a 2hr flight)
During the L ENG ECU test, the engine would rev up and then hang at just under 1800 rpm and would not increase any further to do the prop cycle. It would increase the load up to 45% but engine RPMs would stay constant... it was like someone pressed the PAUSE button in the middle of the ECU run-up and it would just hold RPMs there. So we aborted the run-up (remove our finger from the ECU test) and then it threw an ECU failure for whichever ECU was being tested. We pulled the pulled the breaker on the failed ECU, let it reset... everything cleared, and we did another ECU test, and this time it passed. On departure we did a power check, both engines produced full power, and we departed and flew home without incident.

2nd Occurrence, 12/2/2021 (plane sat for 3 hours after an 1hr 20min flight)
Yesterday, we were flying back from Rexberg, Idaho -- and on departure had the same experience as Sedona, and it resolved just as quickly. On the way home we were dropping off a passenger at Bountiful Airport, however, and ended up having a much worse experience.

3rd Occurrence, 12/2/2021 (plane sat for 1 hr or less after a 1 hr flight)
After dropping off the passenger in Bountiful, we fired up the plane and headed for the run-up area. This time the run-up failure occurred again, but this time was NOT easily resolved. We experience the same thing as in Sedona and Rexberg.

During the L ENG ECU test, RPMs would climb and then hold at just under 1800 rpms and the test would basically pause. Load would keep climbing, but RPMs would not. We'd release the L ENG ECU test button, and the engine would calm down... and then we'd get a L ENG ECU A or B FAIL annunciation depending on how far through the test it got. So, like before, we pulled the failed ECU breaker to reset it, and tried again.

But the symptom repeated itself. We did this a couple of times, and decided to abort the takeoff. Beecause of the runway situation, however, we did a taxi back on the runway, and used it as one last opportunity to see the engines. So we taxied onto the runway, and did an available power test. L ENG would only product about 70% power. Definitely abort this takeoff.

So we taxied back, and called to arrange a ride... and as we were waiting we went through the POH again and left the engines idling. Just as we were getting ready to shutdown, we decided to do another test. We did a L ENG ecu test and everything passed. So we did an available power test, and got 99% on both engines... One of the other pilots I fly with does a lot of certifications with pilots flying experimental aircraft. He and I discussed the symptoms, came up with an emergency plan, tied in with SLC tower, and prepared for our departure for a quick flight south back home. Before departure we did another available power test, got 99% on both engines, and continued the takeoff without incident, and did our quick flight home.

N100DA Grounded
So now we've grounded the plane... we're based out of KSPK in Spanish Fork, UT (home of Draco and Scrappy for those who follow)... and unfortunately, don't have any local A&P that is Austro Certified. So we're working with Diamond to get a cable and download data from the onboard computers...

The symptoms seem to develop AFTER the aircraft has been flown... Since the plane has been cooling off/sitting overnight, we're going to test it on the ground and see if it happens again even if the plane is COLD.

We believe it is a governor issue, but we'll see.

if you guys have any additional ideas on what might be happening, let me know. Otherwise, we'll keep you posted.
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Re: L ENG ECU FAIL during runup...

Post by UTMark »

Update: We went over and did multiple run ups on the plane after the engines were cold and could not reproduce the issue. It does seem as if this issue is manifesting itself after the plane has been flown for some period of time and the engines are hot.
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Re: L ENG ECU FAIL during runup...

Post by CFIDave »

If it is a governor issue (strong possibility, since that's mostly what's being tested during the automated run-up), a relatively easy way to check for this is to have an A&P swap governors between engines -- and see if the problem then follows to the other engine.

Years ago on my DA42-VI I had one engine with power that came up more slowly than on the other engine. On one takeoff before aborting I almost departed the side of the runway due to asymmetric power. To get the plane home I had to run both engines up to full power (waiting for one engine's % load to catch up to the other) at the end of the runway, then release the brakes.
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Re: L ENG ECU FAIL during runup...

Post by jast »

We had the similar behavior with our left engine. After stops for a few hours with increasing temperature the ecu test pass didn’t pass. After reading out the ECUs (we actually now carry a laptop with cable to be able to do this anytime) and talking to Diamond support we found that the left engine govenor did hang in the most extreme position during the ECU test. There is even a fix which readjusts the govoner end position just a little to make this less likely. The good news is that the govenor never reaches the maximum position in flight and the most extreme position is on the ground at takeoff. So if the engine produces clean >98% at the power test and holds it during the first meters it will work just fine for the flight. It is more a testing robustness issue. Obviously we didn’t want to take any chances and first tried the adjustment fix asap. We did a few flights before the issue came back and then got a new govener (on warranty) asap. But with this knowledge and after confirmation with Diamond of the ECU readout data we did not ground the plane but did the flights back home and to the Diamond service in Egelsbach.

Btw: It was more likely to pass the ecu test with a warm engine when cycling the prop/power manually in area 50-60% a few times before the ecu test.
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Re: L ENG ECU FAIL during runup...

Post by UTMark »

jast wrote:We had the similar behavior with our left engine. After stops for a few hours with increasing temperature the ecu test pass didn’t pass. After reading out the ECUs (we actually now carry a laptop with cable to be able to do this anytime) and talking to Diamond support we found that the left engine govenor did hang in the most extreme position during the ECU test. There is even a fix which readjusts the govoner end position just a little to make this less likely. The good news is that the govenor never reaches the maximum position in flight and the most extreme position is on the ground at takeoff. So if the engine produces clean >98% at the power test and holds it during the first meters it will work just fine for the flight. It is more a testing robustness issue. Obviously we didn’t want to take any chances and first tried the adjustment fix asap. We did a few flights before the issue came back and then got a new govener (on warranty) asap. But with this knowledge and after confirmation with Diamond of the ECU readout data we did not ground the plane but did the flights back home and to the Diamond service in Egelsbach.

Btw: It was more likely to pass the ecu test with a warm engine when cycling the prop/power manually in area 50-60% a few times before the ecu test.
Awesome insights [mention]jast [/mention]! Thank you. I may DM you for more info!


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Re: L ENG ECU FAIL during runup...

Post by Paul »

UVU at Provo flies 42s. I don't know what kind but they might have an experienced A&P.
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Re: L ENG ECU FAIL during runup...

Post by UTMark »

This is the governor connector right under the coolant overflow valve that we are trying to get replaced. We believe it’s possible that the coolant overflow issue we’ve had could be contributing to this other issue. We’re still waiting on a cable to get more data but got it cleaned up and can still not reproduce this issue without an extended flight. Diamond I guess can’t ship us the cable without going through one of their shops… so Canada > Cali > Utah ImageImage

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Re: L ENG ECU FAIL during runup...

Post by UTMark »

Alright… so the conclusion (we hope) to this saga is that all of the ECU issues seemed to have been caused by our coolant leaks...

The coolant was leaking out of the pressure relief valves and getting into the wiring hardness and connectors for the prop governor and causing issues. Our A&P tore it all down and cleaned up all our wiring/connections that had coolant all over it. And sealed it all back it (better than from factor IMO).

Because pressure relief valves are on back order with Diamond for 6+ weeks or so… he focused on cleaning those up by hand. Then topped off the coolant in each engine and bob’s your uncle. Everything’s been good again.

We did multiple engine run-ups w/ no errors on the computers, a solid test flight, and another flight, and so far so good. Although our suspicion is that we’ll be needing to order replacement pressure relief values soon.


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Re: L ENG ECU FAIL during runup...

Post by CFIDave »

Mark:

Did your A&P remove the pressure relief valve to clean it? Did he force it open to expose and clean the inside surfaces while still mounted to the side of the overflow tank?

The reason I'm asking is that I've also tried to order a new pressure relief valve (my right engine unpredictably spews coolant after some flights and I'm tired of cleaning up the mess and/or adding coolant), and it's been recommended that I try cleaning the existing valve.
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Re: L ENG ECU FAIL during runup...

Post by UTMark »

I’ll double check, but my understanding is that he removed them and cleaned them “thoroughly.” But I’m not sure what that means exactly. I’ll try to get details.


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