Engine power loss - crosspost AOPA

[ejensen]

Left this morning for a trip the Idaho and Washington. Now back home due to a repeated short power loss. Here are the details as best I can remember. I talked to two A&Ps after we got back and nothing jumped out at them. I'll get it to my mechanic on Monday. Any thoughts appreciated.

Momentary engine power loss – Mooney Executive - M20F

Engine – Lycoming IO-360 A1A with Bendix fuel injection.

Symptom is a noticeable decrease in engine power for several seconds then a return to normal accompanied by change in vibration hardly enough to be called an increase. The change is large enough to be noticed by a non-pilot but experienced passenger and very apparent to another pilot.

The only change to instrumentation is an increase in fuel pressure when the power reduces and a decrease when power returns along with a decrease in IAS. Changing the mixture might have an effect on the duration of the power loss. The duration is 5-10 seconds and toward the end of the flight was happening one or more times a minute. Happened often enough that expected TAS was reduced.

No change in MP or EGT (JPI 700, no fuel flow).

Changing the throttle has no effect on the symptoms.

Changing the prop has no effect.

Switching tanks, no effect.

Electric fuel pump no effect.

Mag check in flight is fine.

Checked fuel ‘finger’ screen.

Leak checked on ground with electric fuel pump.

Checked mixture and throttle linkages.

First noticed briefly May 28th in the PM descending into Denver area from west. Checked closely then and test fight could not duplicate. Flew 16 hours after doing commercial training including the day XC and nothing noticed by me or the instructor. Today heading to Idaho the power loss was noticed after climb out to 10,500. Seemed to get worse, aborted trip and returned home.

 

[NC Pilot]

Any chance the fuel tank vents might be plugging? Surprised that there is no change in EGT though if this was the problem.
Something in the fuel tanks periodically drifting over the fuel line port?

Got to think about it some more.

 

[ejensen]

Any chance the fuel tank vents might be plugging? Surprised that there is no change in EGT though if this was the problem.
Something in the fuel tanks periodically drifting over the fuel line port?

Got to think about it some more.

Forgot to mention that we checked both vents and they are fine. Each tank is vented independently.

 

[KennyFlys]

A clogged fuel filter? Blockage in fuel lines?

 

[CJones]

That IS odd. Change in power but no change in EGT. How responsive is your JPI EGT probe? Will it normally measure a change in 5-10 seconds?

Can't remember where the fuel pressure sensor is on the IO-360-A1B6 we fly. If I remember correctly, it is well before the 'spider' on top, which could mean something running through the fuel lines - possible gasket breaking up, etc.

Interested to hear what they find to be the actual culprit.

 

[SCCutler]

FI servo?

 

[dogman]

My 57 172 has the Lyc o360 a1a.

I had a problem that may be simular. I was flying and the rpm would drop 150 to 200rpm for a few seconds and then return. I could feel it but but as you described just a passenger would have not noticed. I could see the difference in fuel pressure as it happened. No change for the manifold pressure it was steady. I do not have a EGT or Engine Moniter yet!

But as I was landing I stayed high until I could make the field, pulled the power and slipped it in making sure I could make it if I lost all power. But I could feel the rpm changing as I came in power off, kind of a slight surging. It was the Prop govener. It only had 15hrs on rebuild.

I do not know if this will help but I hadn't noticed the surging on short final, my mech. said it would have been more difficult to diagnos.

Hope you find the problemn and it is not to expensive to fix.

Jon

 

[bbchien]

Pull and cut the filter. Make SURE you don't have shreds....

 

[charlie]

As I posted on the other board it's blockage to or in a fuel injector nozzle evidenced by the increase in indicated fuel pressue when the power loss is happening. If you had a multi probe egt you could know which cylinder it is in about a minute. Charlie Melot Zephyr Aircraft Engines

 

[KennyFlys]

As I posted on the other board it's blockage to or in a fuel injector nozzle evidenced by the increase in indicated fuel pressure when the power loss is happening. If you had a multi probe egt you could know which cylinder it is in about a minute. Charlie Melot Zephyr Aircraft Engines

That goes along with my fuel line blockage idea but wouldn't the loss of flow in an individual nozzle have to be pretty significant or for a good stretch of time for it to be noticeable?

 

[gismo]

That goes along with my fuel line blockage idea but wouldn't the loss of flow in an individual nozzle have to be pretty significant or for a good stretch of time for it to be noticeable?

I'd think that would be rather obvious on the JPI especially if it was in normalize mode.

Eric, have you downloaded the stored data in the JPI? There may be some valuable evidence there.

One must consider what could cause a significant power loss without noticeable changes in MP, RPM, and EGT. Of course, any change should have some effect on EGT, but that effect could be small enough to miss. The possibilities I can think of are a restriction in the exhaust, a change in ignition timing, or a change in valve timing on one or more cylinders.

 

[Tom-D]

I'd think that would be rather obvious on the JPI especially if it was in normalize mode.

Eric, have you downloaded the stored data in the JPI? There may be some valuable evidence there.

One must consider what could cause a significant power loss without noticeable changes in MP, RPM, and EGT. Of course, any change should have some effect on EGT, but that effect could be small enough to miss. The possibilities I can think of are a restriction in the exhaust, a change in ignition timing, or a change in valve timing on one or more cylinders.

Can you explane how that could occure when the entire valve linkage is mechanical

 

[KennyFlys]

Can you explain how that could occur when the entire valve linkage is mechanical

Adverse wear? I'm just guessing. But, it seems like the symptoms would be more systematic.

 

[ejensen]

I'd think that would be rather obvious on the JPI especially if it was in normalize mode.

Eric, have you downloaded the stored data in the JPI? There may be some valuable evidence there.

One must consider what could cause a significant power loss without noticeable changes in MP, RPM, and EGT. Of course, any change should have some effect on EGT, but that effect could be small enough to miss. The possibilities I can think of are a restriction in the exhaust, a change in ignition timing, or a change in valve timing on one or more cylinders.

I wish I could download the JPI. Mine is a pretty old install. It was the original JPI engine monitor upgraded to an early 700. I'm not sure it has the download option. If it does it wasn't wired.

The fact that the only definite change in instrument reading during the event is the increased fuel pressure leads me to the fuel system and a restriction. I don't know enough about how the Bendix system works to guess what could be wrong so the fuel flow can reduce without showing on the EGT.

I flew for over an hour so am pretty sure of the observations. Had a second pilot with me most of the time.

 

[ejensen]

FI servo?

That's what I'm thinking although the fact that it is intermittent and possibly heat related cast some doubt.

 

[gismo]

Can you explane how that could occure when the entire valve linkage is mechanical

No. Just listing the potential, not necessarily plausible causes. I could see how the valve timing could be off by assembling the engine incorrectly, but that sure wouldn't explain an intermittent power loss. Any chance that one the gears that drive the camshaft could become slightly loose? I've never heard of such a thing. I guess one other marginally plausible concept would be something that blocked the flow of oil to one or all lifters, but even that doesn't sound like something that could come and go quickly.

BTW, any idea what the consequences of a sticking intake valve would be? Seems to me the engine would backfire, but I don't know if you'd be able to tell that was happening at high power.

 

[gismo]

I wish I could download the JPI. Mine is a pretty old install. It was the original JPI engine monitor upgraded to an early 700. I'm not sure it has the download option. If it does it wasn't wired.

JPI used to offer the memory function as an option but started making it standard several years ago. FWIW it appears that many with the memory were installed without the data jack because the owner and or mechanic didn't think it was worth the effort (wrong!!). I believe the initial screen shows the amount of memory left if the option is installed. Also JPI will probably upgrade yours for a few hundred bucks and if so now's probably the time to do it.

The fact that the only definite change in instrument reading during the event is the increased fuel pressure leads me to the fuel system and a restriction. I don't know enough about how the Bendix system works to guess what could be wrong so the fuel flow can reduce without showing on the EGT.

There's just about zero chance that any change in fuel flow that would affect power wouldn't show clearly on the JPI in normalize mode. If you were in percentage (opposite of normalize) mode you could miss something along that line unless you were staring at the display the whole time. If you were operating ROP, it would take a very large change in fuel flow to affect power, on the lean side not so much.

I flew for over an hour so am pretty sure of the observations. Had a second pilot with me most of the time.

 

[ejensen]

JPI used to offer the memory function as an option but started making it standard several years ago. FWIW it appears that many with the memory were installed without the data jack because the owner and or mechanic didn't think it was worth the effort (wrong!!). I believe the initial screen shows the amount of memory left if the option is installed. Also JPI will probably upgrade yours for a few hundred bucks and if so now's probably the time to do it.



There's just about zero chance that any change in fuel flow that would affect power wouldn't show clearly on the JPI in normalize mode. If you were in percentage (opposite of normalize) mode you could miss something along that line unless you were staring at the display the whole time. If you were operating ROP, it would take a very large change in fuel flow to affect power, on the lean side not so much.

I'll watch closer when th JPI boots but I don't remember anything about memory.

I didn't think to go to normalize mode. I did watch the JPI closely after determining none of the other trouble shooting changed things. Problem was the event is short enough it was hard to cycle through all four before the power restored.

I was 80 ROP when when first noticed, then I tried various settings from full rich to LOP. Normal changes on the JPI but the event occured at all mixture settings.

 

[ejensen]

Talked to my mechanic this morning. Can't get in until tomorrow morning. His first question was when was the muffler last rebuilt. He thinks it is a broken baffle partially blocking the exhaust. Would this show on the JPI? He doesn't think the fuel pressure change in enough to be the problem just the result of the reduced power.

 

[gismo]

Talked to my mechanic this morning. Can't get in until tomorrow morning. His first question was when was the muffler last rebuilt. He thinks it is a broken baffle partially blocking the exhaust. Would this show on the JPI? He doesn't think the fuel pressure change in enough to be the problem just the result of the reduced power.

I don't think you'd see anything obvious on the JPI, but you shouldn't see an increase in fuel pressure either. I think you'd see a slight increase in MP due to a reduction in airflow. With Continental FI that would have no effect on the fuel flow or pressure AFaik, and if this was Bendix FI I'd expect a slight drop in FF (but I'm not certain of that).

 

[ejensen]

Well, spent all day trouble shooting and finally in the last 1/2 hour found the problem. #4 cylinder is bad. Not sure what is wrong but compression check is bad and the crackcase show pressure when we finally got the event to occur on the ground. Symtoms sure pointed toward fuel. Stumped a good AI and a good engine mech for most of today. Glad to find the problem. Sorry it wasn't an easy, cheap fix. But the cylinder shop is where the plane is, so shouldn't be down two long.

Thanks for all the ideas, suggections.

 

[Let'sgoflying!]

Sorry to hear it Eric, awful to have to put plans aside.
At least you are at home field. Had us all scratching our heads. Would be nice to resolve some of the diagnostic questions

 

[ejensen]

Sorry to hear it Eric, awful to have to put plans aside.
At least you are at home field. Had us all scratching our heads. Would be nice to resolve some of the diagnostic questions

I'll post a follow up after they get the cylinder torn down. I'm thinking rings not valves. Valves should have shown on the JPI. Plus it would have been very rough. I did have slightly higher AL in my last two oil analysis. Checked compression then and it was fine, high 70s. I think as Tom D says, the engine was talking to me, if only a whisper. I didn't hear it.

 

[Let'sgoflying!]

Yeah, rings if the escaping was heard in the oil filler not the exhaust....
broken ring or? piston defect? barrel?

Hope no metal in the case (crossed fingers icon here)

Why it was intermittent is a bit odd to me. Shifting ring pieces?

 

[ejensen]

Yeah, rings if the escaping was heard in the oil filler not the exhaust....
broken ring or? piston defect? barrel?

Hope no metal in the case (crossed fingers icon here)

Why it was intermittent is a bit odd to me. Shifting ring pieces?

I seem to remember something about rings 'rolling' but very vague.

 

[ejensen]

Got the cylinder off today. The oil ring was in broken pieces for a couple inches and the other rings worn more than normal. Both mechanics said it was heat. The rings would bend but not break. Neither could explain my on/off again symptoms other than suggest it might have been the location of the break, right above a drain hole, and the alignment of the other ring gaps. Everything else appears good. Should know about valves tomorrow.

I try real hard to keep things cool. Guess I didn't try hard enough. Even long climbs in the summer I worked to keep below 400. It was also mentioned that a long ground hold can heat up the barrels/rings while the tops still show cool. I had a couple fairly long waits last summer.

Since #3 runs hotter than #4 we're going to pull it too. Got to trust the engine.

 

[tonycondon]

Got to trust the engine.

especially out where you are flying. i hear you on the temps too. I try my best to keep the super cub under 400 on CHT but in midsummer with a draggy glider its tough.

 

[Let'sgoflying!]

Don't look for ways to blame yourself Eric, sometimes these things just fly apart for reasons having nothing to do with the operator. In fact I sometimes think these things are made from scrap metal these days.
Heat? If they see heat on the oil control ring, its probably from riding sideways up and down the barrel. If an engine is run too hot, there are other places it would show up a lot sooner. You mentioned checking the valves....for interest's sake? I would have thought you'd be getting a new cylinder anyway - did the ring not score the barrel?

 

[ejensen]

Don't look for ways to blame yourself Eric, sometimes these things just fly apart for reasons having nothing to do with the operator. In fact I sometimes think these things are made from scrap metal these days.
Heat? If they see heat on the oil control ring, its probably from riding sideways up and down the barrel. If an engine is run too hot, there are other places it would show up a lot sooner. You mentioned checking the valves....for interest's sake? I would have thought you'd be getting a new cylinder anyway - did the ring not score the barrel?

Jim didn't feel anything. But the cylinder shop will break it down tomorrow. They share a building so it is very convenient, might be ready to put back on tomorrow. Since it off and on the bench might as well check the valves and guides. The other two rings had lost temper? They would bend and not break when twisted. Both mechanics say this indicated things got hot for while.

 

[gismo]

Got the cylinder off today. The oil ring was in broken pieces for a couple inches and the other rings worn more than normal. Both mechanics said it was heat. The rings would bend but not break. Neither could explain my on/off again symptoms other than suggest it might have been the location of the break, right above a drain hole, and the alignment of the other ring gaps. Everything else appears good. Should know about valves tomorrow.

I try real hard to keep things cool. Guess I didn't try hard enough. Even long climbs in the summer I worked to keep below 400. It was also mentioned that a long ground hold can heat up the barrels/rings while the tops still show cool. I had a couple fairly long waits last summer.

Since #3 runs hotter than #4 we're going to pull it too. Got to trust the engine.

Your CHT probe measures the temp of the head, not the cylinder barrel. If something is disrupting the airflow over the cylinder it could be getting a lot hotter than the head. Worst case would be to have significantly different temps around the cylinder. Check your baffles carefully. Also IIRC, rings can be damaged when installing, perhaps yours suffered from that.

 

[ejensen]

Your CHT probe measures the temp of the head, not the cylinder barrel. If something is disrupting the airflow over the cylinder it could be getting a lot hotter than the head. Worst case would be to have significantly different temps around the cylinder. Check your baffles carefully. Also IIRC, rings can be damaged when installing, perhaps yours suffered from that.

That what the engine mechanic was saying about extended ground runs. I thinking it might be that. I had a couple of 20+ waits in hot weather a ABQ and TUS last year. I have my JPI alarm set to 420 and don't recall it going off. Anytime I get over 400 I lower the nose.

Not sure about damage, always possible. But the fact remains the rings exhibit evidence of overheating on both rear cylinders. Right now the plan is to leave the front alone. I've got the weekend to think about that while driving to a fly-in breakfast at Granby, CO (GNB) .