RPM loss

G

Glasair

Filing Flight Plan
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ermed5
Hello all. I recently purchased a Glastar with a Lyc O-320 (100hrs since OH) and M/S carburetor. Brought it home without incident. It has a FlyEFII legacy electronic ignition running two coils.

About 3 weeks ago, I was out for a routine ride at 3500ft, and engine power suddenly and quickly decreased to idle... panic time! Not windmilling, and didnt need to restart. Just like your CFI giving you a biennial and 'lets do a practice engine out'. No sputter, no roughness. Unfortunately, I did not keep a close eye on any Dynon HDX changes... was too busy. But about 20 seconds into this, engine power came back up to cruise. I headed straight back to home base, and about 15 miles out, it happened again. About 20 seconds of power down to idle, then it returned to cruise power. I did what I could... mixture rich, check ignition, (no aux fuel pump in this machine), and fuel on (only has on/off). Landed without incident.

We removed the carburetor and took it to a well known shop, but they said it looked fine and bench tested ok (and it even has the latest float). We reinstalled it, and then the fuel pressure transducer stopped working. I replaced that. Made sure air filter to bottom of carb wasnt kinked, and even checked valves (some CHT's re a bit high during this event). Drained all tanks a number of times... no water. I've been up for 2 rides in the pattern, to be safe. I now notice RPM changes on the ground. They are minimal. But today, after running it on the ground for a while, I saw RPM changes at idle. I made sure the friction lock was tight, set it at 1000rpm, and just watched it. It vacillated slowly from 1000-1100, then down to 940-950, then back up again, with pauses in between each change. I know the Dynon unit is very sensitive, but watching these idle changes worries me. If its doing this on the ground, it can easily happen up at altitude. I must mention this, tho... prior to this event, I noticed a number of barely noticeable minimal lurches in my seat while flying. No change in engine noise, no changes in power or other settings... but just an occasional 'torso moves forward in your seat'... like a very quick power decrease burp.. but with no other changes.

We initially focused on the carburetor... but with it being inspected and repaired, that shouldnt be the issue (unless it truly is a carb item and needs to be replaced). Maybe this is gunk in the fuel tanks? If it was, wouldnt there be sputtering/fuel starvation? I've drained so many times, and fuel remains totally clean. I also had Dynon look at the data logs, and they saw the power/RPM loss and fuel flow decrease during the event... but fuel pressure stayed normal.

I've messaged colleagues, and some folks had similar issues, with most turning out to be water in the tanks. A few did mention bad carburetors/floats/cotter pins in the bowl, etc.

Something is amiss. Any comments/thoughts/suggestions would be very welcomed. Thanks!
 
Glad you are ok, probably not helpful but

Fuel, Air, Spark
 
Glasair said:
Something is amiss.
Click to expand...

Component(s) within your electronic ignition system appears to be on the fritz. You questioned every portion of your power generation, except that one. Why is that? Don't answer that I'm being rhetorical.

Carburetor ice doesn't drop RPM suddenly like that, to regain it in [relative to icing] short order. Your (single mechanical?) fuel pump px is steady at the sensor, glastars are high wing anyways so gravity feed is sufficient to feed a float carb without lurching. Water has been ruled out.

Good luck on the troubleshooting. Electronics are a pita when all you wanna do is go fly.
 
Fuel pump?

A year ago when we were leaving for a trip the engine burbled a bit not long after takeoff. In hindsight it happened shortly after turning off the electric backup. The plane flew fine when I turned around and went home (of course). I had it swapped out and indeed the diaphragm had a leak.

Watching the engine monitor, the fuel pressure and flow were very low unless the electric pump was on.

Something to consider.

Add: this was posted seconds after the above
 
Fuel pump and EFII are next on the list. We only have the engine driven fuel pump. I doubted carb ice… but carb fuel floats have been known to be cranky. I am gonna take a very close look inside tanks… debris that we can’t see?
 
Sounds like ignition issues, not fuel.
 
I am going to send the EFII unit back for bench testing. But interestingly, when we removed the carburetor, my mechanic commented that fuel wasnt coming out of the fuel line (to carb) maybe as strong as it should have been... which leads me to think of something being restricted further up the line? This, then, reminded me of that occasional slight 'lurch' in my seat, when in cruise/at altitude. Maybe this IS a bad fuel pump... and, during the prebuy, the mechanic happened to find an odd noise in the right aileron... like a small tool left inside when moving up and down. Turns out, it was a mud daubers nest!!! Of all places! Which leads me to think of what/who else is living in there !!! Hence, further inspections. I feel like a detective! Ahhh...the joy of the experimental world!
 
I appreciate all the comments and feedback!
 
I found many pounds of mud daubers and wasps nest in my plane in the last 7 years. I am still finding them all these years later.
This was about 1/2 of what I found during my first annual 2018.
153.jpg

Every annual since I have found more that has broke loose.
This was just last month when I had the flaps off.
IMG_3951.HEIC

Good luck finding your problem. That is another mud dauber nest.
IMG_3815.JPG
 
In line with the post above make sure your fuel tanks are properly vented and the vent system has no clogs. I don’t think it’s ignition as that is usually a plug not firing and would not cause the engine to go to idle. It’s also instantly easy to diagnose that with a HDX.
Go through the entire vent system. Make sure there are no obstructions. You should also do a flow test. Your mechanic should have done this. It needs however to be checked after you let a gallon or two flow through the system.
 
Jeff767 said:
In line with the post above make sure your fuel tanks are properly vented and the vent system has no clogs. I don’t think it’s ignition as that is usually a plug not firing and would not cause the engine to go to idle. It’s also instantly easy to diagnose that with a HDX.
Go through the entire vent system. Make sure there are no obstructions. You should also do a flow test. Your mechanic should have done this. It needs however to be checked after you let a gallon or two flow through the system.
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Yes I was thinking about the vent system, very important and if you found a mud dauber nest that means it sat around long enough for them to build the nest. Where else did they build nest?
 
Wow... thanks for the pics... and i had to chuckle... maybe i AM hiring the wrong person to fix this.. need an exterminator! LOL.

This machine was in the Atlanta area for a few years before it came up to the tundra of the upper midwest. Hot and humid down there. Always hangared. But clearly, with a mud daubers nest in one aileron, hangar or not, they wanted better accommodations! Even better reason to continue searching for out of state residents living in my machine. I now see I should have picked up better with the mechanic's comment as to "gee, your fuel is flowing out of this line (into the carburetor) a bit slower than we would normally see".

All the HDX data showed was several low power events/RPM/manifold pressure and fuel flow, but fuel pressure was good.

Thanks for the additional comments... the search continues. My gut feeling now is that something is obstructing something.
 
I had a similar issue on an old shovel head motorcycle, eventually found the fuel line was degraded internally and a little flap of rubber was randomly acting like a flow restrictor.
 
FWIW... E-10 auto fuel will degrade "aircraft" fuel hose to the point that they swell shut and can also degrade fiberglass fuel tanks.
 
I doubt that Glasair plane is 40 years old like my antique is. This is the coupler hoses I replaced on mine a few years ago. Not all were original but all needed to be replaced.
IMG_0586.JPG
 
Glasair said:
I am going to send the EFII unit back for bench testing. But interestingly, when we removed the carburetor, my mechanic commented that fuel wasnt coming out of the fuel line (to carb) maybe as strong as it should have been... which leads me to think of something being restricted further up the line?
Click to expand...
It will be a bit slow because it has to squeeze past the bypass check valve in the fuel pump. If that was really a problem (a restriction somewhere), the engine would die and pretty much stay half-dead, and it likely wouldn't go to idle all that quickly.

Spark. 90% of the time it's the spark. Everybody chases fuel because they can sort of understand fuel flow. Like water in a garden hose. They have a lot harder time visualizing what goes on in the ignition system. You said this:
Glasair said:
It has a FlyEFII legacy electronic ignition running two coils.
Click to expand...
So, is this the system?

1710524957191.png

Well, that raises some questions. That system has this trigger assembly:

1710525010089.png

If it comes loose both ignition sources are going to act up. Both of them. A lack of redundancy there.

And the bigger question: How is the power supplied to the two controllers? One or two switches? One is bad. Does the power come through one or two breakers? Does it come off one bus? Is there a standby battery for one of them? Is there anything else common to both systems? Any commonality between the two systems is a potential source of trouble; if something fails, all the sparkplugs fail.

What governs the spark retard during cranking? That there would be a spot to check. Timing going to TDC would result in a really big power drop and lousy idling.

Everything between the battery and the ignition modules needs to be checked. The MAP sensors also need checking, and if they're fed by one MP hose off the manifold, that might be compromised, too. A leak there will raise the MAP in the sensors and the system thinks it's at idle and reduces the spark advance.
Check all the fancy system connectors, too. Look for looseness, and for chafing wires shorting against the engine or airframe. A poor electrical connection is like a plugged fuel hose. A short to ground is like a big leak of fuel. Not so hard to understand that way.

These sorts of thing are why most new airplanes still come with magnetos. Sure, they're ancient technology, but we use a lot of ancient technology every day. Hydroelectric dams. Guns. Knives. Hammers. There just isn't much new stuff to replace those things. A magneto keeps firing even when the airplane's electrical system fails totally. It generates its own power. Electrical systems are famous for problems. My Power Mechanics instructor in high school in the late 1960s told us that 90% of engine troubles are electrical, and in the many years since then I have found him absolutely right. That goes for alternator and generators, too. Skimp on the maintenance, and they will fail.
 
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Yes and no. Its not that specific one above... its an original legacy system. It has one ECI unit with two coils. I've been in touch with them, and they say it either works, or doesnt work. I cant argue that one. Runups are as usual. I'm now thinking this is a fuel issue somewhere.... maybe a bad engine driven fuel pump.. maybe a blockage somewhere I just havent found yet. But yes... lotsa stuff needs to be checked.
 
I had a very similar experience in my C206 right over the peaks of the White Mountain range in New Hampshire, went through the checklist and headed for the only "potentially" suitable landing area to have a crash. Then the engine came back to life, then it quit again and did that four or five times over the next few minutes as I limped toward a better landing option. When I landed I had everything checked out and mechanics could find NOTHING to explain the problem. Ultimately, I'm 98% sure that what was happening was leaking fuel tank (bladders, actually) which dissolved some of the adhesive in the tape inside the wing and then was pulled back into the tank, possibly aided by a venting problem. The "goo" was soluble in gas, so it appears that what was happening was that small bits would break off, clog the delivery system until fuel moving past it dissolved the goo away and normal fuel flow resumed. That was about three or four hundred hours and several years ago when we replaced the bladders in both tanks, and the problem never recurred.

I'm a little embarrassed to say in retrospect that I had noticed a few tiny droplets of blue goo on sumping of the tanks, followed by clear fuel for the rest of the sump. Before the bladders were replaced I was able to get another drop of the stuff in the sump collection and by stirring it vigorously was able to make it disappear into the fuel sample.

I filled out an ASRS report (not for any kind or "immunity") and surprisingly got a phone back call to discuss it further. It's clear that the situation is rare, but we never got any better explanation.
 
Glasair said:
Yes and no. Its not that specific one above... its an original legacy system. It has one ECI unit with two coils.
Click to expand...
That's bad. All spark hanging on one little box, its power supply, it's MP sensor, its trigger. If there's a flaw anywhere, you get the symptoms you have.
 
Not sure if I stumbled onto the culprit. While waiting for a new fuel pump to arrive (just in case it WAS a bad pump), I continued my search. When blowing air into the vent at the tips, all I could hear was air exiting very close to the vents themselves... no bubbles or noise in the tanks. Today, while struggling with one stripped phillips screw on the left side, I went over and removed the right tip. Lo and behold.. the Andair check valve was rolling around freely, and the vent lines were completely disconnected! I am going to assume the same thing is happening on the left... altho the right tank was at 2-3 gallons left after that memorable ride, and he left side was at 1/2. Would this/possibly these be the cause of the sudden drop in power? IMG_0925fuel.jpg
 
Glasair said:
Would this/possibly these be the cause of the sudden drop in power?
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Not likely. Why would the power come back again? And how would that make the idle RPM wander around?

Venting issues have brought down numerous homebuilts. Everything runs fine on the ground, but in flight the engine quits. That might have to do with differential pressures in venting between main and header tanks, where the venting system was not designed to keep the tank pressures equal. The header might get a higher pressure in flight as the airflow strikes its vent differently, and at that point the fuel from the main tank won't flow into the header on its way to the engine. The header goes dry. Or the vents are generating suction in flight and holding the fuel back and killing the engine. In either case, the engine stays dead because the airflow around the airplane maintains the defect until the forced landing or crash.

Those valves have likely been rolling around in there for sometime, but the airplane still flew. You might have been losing a bit of fuel in uncoordinated flight, though.

What does the electrical stuff look like? Everything tight? No looseness that can't be seen until you tug on things a little? Are you using a standard mag switch? The ACS switches have ADs on them due to the fact that the starter function can burn their contacts and affect magneto operation. Never forget that electrical problems are MUCH more common than fuel problems.
 
Now I'm really confused. I managed to get into the other wingtip, and found the same... check valve rolling around and line disconnected. I am told that blowing into the lines can do that. I dont recall if we removed the caps when we did that. If we didnt, then my bad.

No header tank here. No standard mag switch. Individual throw switch for each ignition coil. Checking further.
 
If that is a check valve it is designed to vent out. If you blew in it very well could have blown the lines off. Thus not related to your power loss.
 
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