Engine Won’t Start (Intermittent)

[Nicolas Bennet]

Brief Summary:

On two occasions (27 May and 21 June) my Arcus-M engine has refused to start.  It then failed to start on many subsequent attempts the same day and on following days.  Suddenly, without explanation, it starts and runs properly.  

Both times the failures occurred on the ground after landing, when I tried to start the engine to taxi back to the hangar.  I flew 13 times (26 starts) and had 250 minutes of engine time between the two failures, and have flown twice (4 starts) since the second failure.  The engine has never failed after it starts running. It has only failed when I try to start it. Since no one can explain what caused the engine to fail or to start working, I do not have high confidence that I won't have a failure again.

Things we did before the problem mysteriously went away and the engine started:

We confirmed a good battery charge and that we have ignition.  At my mechanic's instructions we either unplugged and replugged connectors or confirmed other connectors looked good, e.g. wiring connections at MCU & powerplant operating units in panel.  We confirmed the latest Trijekt software version.  We ran the Trijekt program to confirm the throttle sensor is getting a good reading and the rpm reading is reasonable and the air pressure and temperature reported by the software match the ASOS.  We did not smell fuel, and the problem occurred even the next morning when the engine was cold and battery fully charged.  As always I started the engine with the throttle at full idle, but also tried moving the throttle forward a bit, and when I tried starting in redundancy mode, I had the throttle slightly cracked and moved it forward as the engine was cranking the way I would with a non-fuel injected two stroke engine.

Suspecting a fuel problem we confirmed fuel pump operation, drained fuel from both the fuselage and directly from the wing tank (after shaking the wing) and all looked good.  We confirmed fuel pressure.  Finally we changed the injectors on the redundancy system.  We did not change the non-redundancy injectors because they are harder to access and we thought we'd start with the easiest test.  We then tried to start the engine in redundancy mode.  It started, but without explanation, the engine ran on the non-redundancy system (with the original injectors).  We subsequently had both sets of injectors checked by a qualified mechanic who determined none  showed signs of fuel contamination or clogging. No one understands what changed to make it work.

The first time the engine failed (on 27 May) we changed spark plugs (which were fairly dirty with carbon build-up) and drained fuel, which showed some very fine silt like contamination.  Still the engine would not start.  Then, at my mechanic's suggestion I tried to start in redundancy mode and it worked.  For unexplained reasons it then also worked in non-redundancy mode as well.  No one understands what changed to make it work.  

Summing up:

The consensus is that the most likely cause is bad fuel, since I did discover bad fuel after the first failure and it is the only thing we've found "wrong".  However, the injectors were clean.  It has been suggested that I change the fuel filters, but that is a lot of work and there is no clear sign that they are the issue. 

 It is hard to fix a problem that goes away without explanation. Any ideas are welcome.

 

[Andreas]

When did you drain the last time, may be you had water in the fuel? Take a sample into a jar and check absence of condensation water in the system.
Best regards
Andreas

Mit freundlichen Grüßen
Andreas Balk

[John Galloway]

I had 1.5 seasons of repeated slow and rough or failed ground starting with my V3M 2625 01i engine which was not improved by new spark plugs x 2, draining and changing the fuel etc.  The spark plug caps were only slightly sooty but cleaning made no difference.   2-3 weeks ago I changed the factory fitted PVL 5kOhm plug caps for new NGK LB05FP plug caps and the engine seems to be transformed for the better.  It now starts immediately,  warms up more smoothly and the max rpm is about 150 rpm better than it ever was before.   These plug caps are a push on fit directly on the the threaded stud without the removable nut and that seems to give a more secure contact which might be helping.  I am very surprised to find that such a simple and inexpensive change could make such a difference and it might be worth trying.

[Nicolas Bennet]

Thanks for the suggestion.  Yes, I did check for water in the fuel.  I should have made that clear in my problem description.  I wish it was that easy!

[Nicolas Bennet]

Thank you for the suggestion to try the NGK plug caps.  I have ordered them.

[Chester Fitchett]

Treating your solo engine as a large lawnmower - there are three reasons why an engine won't start.  Air, Fuel, and Spark.

I think we can assume your engine is getting lots of air.  So we are down to Fuel and Spark.

In your situation, I would think about the following ideas.  Definitely talk to your mechanic.

1)  I believe you can see the fuel injectors working by taking off the air filters.  Confirm you are getting shots of fuel when the engine is cranking.

2)  Check that the Engine Control display is indicating RPM correctly when the engine is cranking.  This would be my first check.  Could be a marginal tachometer pickup.  I think there is an LED built into the pickup, another way to see if the Trijekt is getting a good signal.

3)  Any possibility the engine is flooding and soaking the spark plugs while you are flying?  Do you fly with the computer on and fuel valve open?  Seems interesting that the problem takes days to resolve.

Chester

[Henrik Holm Kristensen]

We had a problem with starting our engine a couple of years ago. Not always. But from time to time. 

Found the problem to be a broken wire on the tacho sensor. Just where the cable entered the sensor. 

Broken due to vibrations. 

Found the fault, when the engine was running on gruond, and trying to mangle all the cables on the engine that i could wiggle while the engine was running. 

When the engine wibrated when running, there was a reasonable contact annyway, so the engine could run. 

But when trying to start, the vibration level was someting to small to make the two wire ends touch each other. 

I believe there is a counter in the engine control, that you can check and see if there is some missing tacho pulses. 

You need a pc to get the information out of the engine control. 

Best regards

Henrik Holm Kristensen

Arcus no 58

Get Outlook for iOS

---

From: schempp-h...@googlegroups.com <schempp-h...@googlegroups.com> on behalf of Chester Fitchett <fitc...@phidgets.com>
Sent: Sunday, July 4, 2021 6:47:53 PM
To: Schempp-Hirth Arcus <schempp-h...@googlegroups.com>
Subject: Re: {Schempp-Hirth Arcus} Engine Won’t Start (Intermittent)

 

--
You received this message because you are subscribed to the Google Groups "Schempp-Hirth Arcus" group.
To unsubscribe from this group and stop receiving emails from it, send an email to schempp-hirth-a...@googlegroups.com.
To view this discussion on the web, visit https://groups.google.com/d/msgid/schempp-hirth-arcus/4a12700b-5182-471b-b3e6-19186abc6c03n%40googlegroups.com.

[Nicolas Bennet]

Hello Chester,

Thank you for your suggestions

 > Definitely talk to your mechanic.

Yes, I've been talking to him, and he has been talking to Rene and Bernd at Schempp Hirth.  So far no one has an explanation.

 > I believe you can see the fuel injectors working by

 > taking off the air filters.  Confirm you are getting

 > shots of fuel when the engine is cranking.

I'll give this a try next time the engine fails to start.  It has been working since the second failure.

 > Check that the Engine Control display is indicating RPM correctly

 > when the engine is cranking.  This would be my first check.

Yes, both front and back ILEC and the Trijekt program are showing apparently correct RPMs when I crank the engine.  It just won't start.

 > Any possibility the engine is flooding and soaking the spark plugs

 > while you are flying?  Do you fly with the computer on and fuel valve

 > open?  Seems interesting that the problem takes days to resolve.

Yes, I leave the fuel valve open while soaring.  It was my impression that soaking the spark plugs wouldn't happen with a fuel injected engine.  But even that happened, it wouldn't explain why it won't start the next morning.

I appreciate the input.    And congratulations on those amazing winter wave flights!

Nico

[Nicolas Bennet]

Hello Henrik

 >We had a problem with starting our engine a couple of years ago. Not always. But from time to time.

This sounds like my problem

 > Found the fault, when the engine was running on gruond,

 > and trying to mangle all the cables on the engine that

 > i could wiggle while the engine was running.

This is a great suggestion, given how much the engine vibrates, I should have thought of this myself.  I will give it a try.

 > I believe there is a counter in the engine control, that you can check

 > and see if there is some missing tacho pulses.  You need a pc to get the

 > information out of the engine control.

When we ran the Trijekt software it always reported proper RPMs (even when the engine wouldn't start, the ILECs and Trijekt program showed up to 800 RPM).

I wish there was a way to log results from the Trijekt program for later review.

Thanks again for what I think will turn out to be a very useful suggestion.

Nico