Engine Troubles

[lfgbrd]

Edit: This was obviously supposed to go in the Modern Mooneys section, not sure how I messed that up.

Here's a puzzle for you guys.

I have a 1990 J model that was recently upgraded with an EDM930 engine monitor. Annual last May by LASAR.

Sometimes on start the plane likes to backfire at idle. If it's hot it does it a lot. Bring the RPM up to about 1100 and it runs smooth.

In flight, if I lean aggressively (using the ROP leanfinder on the 930) to around 9 gph and temps between 1500-1550, the engine will miss or backfire or something occasionally. Just a slight jerk, you can feel it in your feet. Maybe once every five minutes. I can't do LOP at all, if I get much lower than peak on the lean side I lose power very quickly. If I keep the temps below 1500 it doesn't do it at all. EGTs and CHTs are all pretty tight, except CHT #1 is always about 70 degrees colder than the other three, even on the ground. Before the 930 we had a 700 which also showed a low #1. The probes and wires were all replaced with new ones for the upgrade.

In flight, if you bring the power back to around or below 50% it will sometimes backfire more frequently. Kind of like what happens when you yank the throttle back in a carbureted engine (I'm looking at you, O-300).

My fuel flow fluctuates between 20 and about 25. When I had the old gauges I didn't notice it move much but on the 930 it's constantly moving.

Today, after about 4 hours of problem-free flying, we turned final and engaged the boost pump. As we pulled the throttle to idle, the fuel pressure jumped up between 30 (red line) and 35 (fluctuating like normal) and the engine started backfiring on every other stroke. Turned the boost pump off, the fuel pressure went back down, and the engine smoothed out. Turned it back on, happened again. Pushed the power back in a bit from idle, the pressure dropped and the engine smoothed. I turned the pump back off just to be safe. Tried it on the ground to no effect.

 

Any ideas what the heck is going on? Think the normal bumps are related to that low CHT? Think they're related to the fuel pump issue? Should my fuel pressure fluctuate a few psi from second to second? I never thought a failing boost pump would increase its output. I'm going to my mechanic Monday but I thought you guys might like to try to work this one out. This poor plane has been in the shop more than not since we've bought it...

Oh, and our backup attitude indicator seemed to be failing today too, so that's the next thing.

[MB65E]

I would be scared to see 1500-1550 on any NA engine. I know many people run there stuff there but not me. I'd like to see what the plugs look like. I'd check the standard items. Looking closely at the injectors, plugs and mags. Over rich/flooded may cause the excess fuel to burn in the exhaust. If you can't  find any snoking guns after the ignition, mags, injectors. I would bench test the fuel servo and divider. It sounds like something is going on in the servo, there is a clogged injector, or bad plug or mag.

other questions-

mag hrs? plug hrs?, colander time on servo?

I actually would not fly it until you figure it out. Fuel issues are scary.

-Matt

[carusoam]

Do you have champion spark plugs?  Can you check their resistance?

It seems as if Something is allowing fuel to get to the exhaust pipes unburnt.

PP opinion, not a mechanic...

-a-

[lfgbrd]

  On 12/20/2015 at 4:41 AM, MB65E said:

I would be scared to see 1500-1550 on any NA engine.

-Matt

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It consistently peaks out around 1550-1575 and I would run it about 50 ROP. But in order to keep it from jerking I don't peak at all and just stay below 1500.

  On 12/20/2015 at 4:41 AM, MB65E said:

mag hrs? plug hrs?, colander time on servo?

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One brand new mag (less than 25hrs), one about 500hrs. Both are strong with good timing. I don't know the other components' times. Injectors were cleaned at annual, and I first encountered the problem as I flew home from shop.

I'm not a fan of fuel problems either. I don't fly this plane much at night because of the small issues I have had, but I've never feared that it might completely quit until this afternoon.

 

  On 12/20/2015 at 5:14 AM, carusoam said:

Do you have champion spark plugs?  Can you check their resistance?

It seems as if Something is allowing fuel to get to the exhaust pipes unburnt.

-a-

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I have a feeling that that #1 cylinder is being fed too much fuel and that's causing the low temps and it's dumping the fuel overboard. Not sure how or if that relates to today's boost pump issue, though. It has Champion REM38Es with about 250 hours on them.

 

 

[carusoam]

Are you familiar with the test for FI flows, using identical glass jars?

The plug resistance and injector tests are only things that I have read about here.  It may help when you speak with your mechanic.

best regards,

-a-

[lfgbrd]

Familiar as in I've probably read the same things around here. I have quite a bit of experience maintaining my previous aircraft, a Cessna 150...not much to worry about breaking there. My partner and I are learning how to break all kinds of new things with the Mooney.

[carusoam]

Wait until you do your first owner assisted annuals.  You get to break all kinds of expensive stuff...

Best regards,

-a-

[Ratherbflying]

Did you download the data from your EDM930 for this flight and take a look at it? Also, you might want to (if you haven't already) run the in-flight diagnostic tests described here:

https://www.savvyanalysis.com/articles/in-flight-diagnostics

 

[Yetti]

I vote.  hours on Mags and or fuel servo and or timing

[N201MKTurbo]

I would check your timing for the high EGTs. The MAGs are the most suspect for the backfire. Have you tried to run on one MAG while it is backfiring? 

The boost pump has a pressure regulator and could be set too high. The adjustment is usually epoxied in place and would need to be screwed in to raise the pressure, so that is unlikely. A piece of debris in the regulator might cause it to go over pressure .

[Bob - S50]

1.  You said you first encountered the problem when flying it home from the annual.  That's a good place to start.  Even though it was LASAR, everybody makes mistakes.  In the safety field, after an accident we always started with the last maintenance performed.  Find out what they did.  Change plugs? Reset mag timing?  Change wiring?  Mess with the fuel system?  Whatever they touched, have it checked.  I'm guessing either a weak spark or mis-timed mag.

2.  Not an expert, but I wouldn't worry about the EGT.  It can vary depending on probe placement.  Plus, as Mike Busch or John Deakin (can't remember which) points out, EGT is an average.  Gas is only going out the pipes for 1/4th of the engine cycle.  It heats the probes on the way out and they cool off while the engine sucks, squeezes, and bangs.  Only sees the blow part.  Actual gas temps in the cylinder before the exhaust valve opens is much higher (5000F? - can't remember).

[MB65E]

 5000? Wow. I get the compression makes the temp go up but wow...

 The melting point of the aluminum heads is likely around 1800. Pure aluminum is around 1250, granted it's not pure, and it only happens once per revolution.  And the poor piston... I just think running in the 1500s takes its toll.

The flow check is a good idea. Was the issue as bad 25hrs ago with the old mag? I'd pull the plugs and swap them around to see if it changes cylinders. Should test them in the process. 

Keep digging.

-Matt

[lfgbrd]

  On 12/20/2015 at 4:41 PM, MB65E said:

Was the issue as bad 25hrs ago with the old mag?

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Yeah, the mag died suddenly and replacing it didn't seem to have any effect. Good idea in the plugs, all  check them and I'll make sure they're rotated. 

[carl]

There was a rumor that you mag will quit at 500 hours .

So I am having both rebuilt for no reason except hours.

 

carl

[carusoam]

Carl,

There is also a similarly strong rumor that says swapping them out separately is a good idea.

This way they don't come up on the time schedule at the same time.

Of course, if they are both past 500hrs already...

Best regards,

-a-

[M204ever]

Matt nailed it, don't start "try and error".

Its always the sum of different "minor" issues that can lead you in serious troubles (I mean in flight, not money-vise).

Not that it only improves confidence in the engine, it just makes more fun to operate a healthy powerplant.

[ArtVandelay]

  On 12/20/2015 at 10:45 PM, carl said:

There was a rumor that you mag will quit at 500 hours .

So I am having both rebuilt for no reason except hours.

 

carl

Mine went 1100 hours (slick), in my experience hard starting can be a symptom of mags in need of service.

[Shadrach]

  On 12/20/2015 at 4:41 PM, MB65E said:

 5000? Wow. I get the compression makes the temp go up but wow...

 The melting point of the aluminum heads is likely around 1800. Pure aluminum is around 1250, granted it's not pure, and it only happens once per revolution.  And the poor piston... I just think running in the 1500s takes its toll.

The flow check is a good idea. Was the issue as bad 25hrs ago with the old mag? I'd pull the plugs and swap them around to see if it changes cylinders. Should test them in the process. 

Keep digging.

-Matt

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There is a thermal boundary layer that pervents the cylinders and piston from being subjected to the max heat of combustion. This boundary is disrupted by detonation (small sonic boom from flame front breaking the speed of sound) which is why detonation melts cylinders and pistons.

[Shadrach]

My internet assesment is that the OP has an ignition problem. I believe a high powered mag check would help track down the weak link. My brother scrubbed a trip because he "couldn't lean at altitude". The engine ran fine on the ground With a normal run up.  I flew the plane over the air port and sure enough had one EGT out of line in the climb. I leveled and did a full power mag check. Sure enough, the engine missed on the right mag. In our case we had a plug that would only drop out at high cylinder pressure (It needed more than 25" to miss). 

[LANCECASPER]

  On 12/20/2015 at 10:45 PM, carl said:

There was a rumor that you mag will quit at 500 hours .

So I am having both rebuilt for no reason except hours.

 

carl

Expand  

I would never take both redundant items that are working properly and rebuild at the same time. The most likely time for something to fail is in the first few hours of service.

[Bob - S50]

  On 12/20/2015 at 4:41 PM, MB65E said:

 5000? Wow. I get the compression makes the temp go up but wow...

 The melting point of the aluminum heads is likely around 1800. Pure aluminum is around 1250, granted it's not pure, and it only happens once per revolution.  And the poor piston... I just think running in the 1500s takes its toll.

The flow check is a good idea. Was the issue as bad 25hrs ago with the old mag? I'd pull the plugs and swap them around to see if it changes cylinders. Should test them in the process. 

Keep digging.

-Matt

Expand  

My memory was off by a little.  Here's a quote from a Pelican's Perch article:

"We know that combustion temperatures are in the 3,000ºF to 4,000ºF range, but TIT and EGT "only" run around 1,600ºF, and CHTs down around 400ºF. How can this be? 4,000ºF is more than enough to melt steel, so how does the interior lining of the cylinder survive? Why don't we see hotter temperatures on our instruments? Why doesn't the aluminum piston melt down, when aluminum melts at less than 1,000ºF?

There is a "thermal boundary layer," on the order of a millimeter thin or so, that acts as a buffer to protect the steel cylinder walls and the surface of the aluminum piston."

[MB65E]

Cool...I mean hot!

-Matt

[Guitarmaster]

  On 12/20/2015 at 4:09 AM, lfgbrd said:

Edit: This was obviously supposed to go in the Modern Mooneys section, not sure how I messed that up.

Here's a puzzle for you guys.

I have a 1990 J model that was recently upgraded with an EDM930 engine monitor. Annual last May by LASAR.

Sometimes on start the plane likes to backfire at idle. If it's hot it does it a lot. Bring the RPM up to about 1100 and it runs smooth.

In flight, if I lean aggressively (using the ROP leanfinder on the 930) to around 9 gph and temps between 1500-1550, the engine will miss or backfire or something occasionally. Just a slight jerk, you can feel it in your feet. Maybe once every five minutes. I can't do LOP at all, if I get much lower than peak on the lean side I lose power very quickly. If I keep the temps below 1500 it doesn't do it at all. EGTs and CHTs are all pretty tight, except CHT #1 is always about 70 degrees colder than the other three, even on the ground. Before the 930 we had a 700 which also showed a low #1. The probes and wires were all replaced with new ones for the upgrade.

In flight, if you bring the power back to around or below 50% it will sometimes backfire more frequently. Kind of like what happens when you yank the throttle back in a carbureted engine (I'm looking at you, O-300).

My fuel flow fluctuates between 20 and about 25. When I had the old gauges I didn't notice it move much but on the 930 it's constantly moving.

Today, after about 4 hours of problem-free flying, we turned final and engaged the boost pump. As we pulled the throttle to idle, the fuel pressure jumped up between 30 (red line) and 35 (fluctuating like normal) and the engine started backfiring on every other stroke. Turned the boost pump off, the fuel pressure went back down, and the engine smoothed out. Turned it back on, happened again. Pushed the power back in a bit from idle, the pressure dropped and the engine smoothed. I turned the pump back off just to be safe. Tried it on the ground to no effect.

 

Any ideas what the heck is going on? Think the normal bumps are related to that low CHT? Think they're related to the fuel pump issue? Should my fuel pressure fluctuate a few psi from second to second? I never thought a failing boost pump would increase its output. I'm going to my mechanic Monday but I thought you guys might like to try to work this one out. This poor plane has been in the shop more than not since we've bought it...

Oh, and our backup attitude indicator seemed to be failing today too, so that's the next thing.

Expand  

It sounds to me like an intake leak.  Were it me, I would do this...

https://www.savvyanalysis.com/articles/in-flight-diagnostics

 

[lfgbrd]

Thanks for that.

[MyNameIsNobody]

  On 12/21/2015 at 2:12 PM, LANCECASPER said:

I would never take both redundant items that are working properly and rebuild at the same time. The most likely time for something to fail is in the first few hours of service.

Expand  

That is why there are two...