Rough running IO-360

[RideOrFly]

I'm in the middle of what's turning into a maintenance nightmare, and would appreciate any thoughts/input on the situation. The plane is a 79 M20J, 600 SMOH (150 of that since I bought the plane in May 2022. I don't have an engine monitor and while I'm trying to learn as much as I can, I'm definitely much more pilot than mechanic.

I was flying regularly, and the engine has always been extremely smooth. Compressions in the high 70s consistently, always idled smoothly and performed flawlessly. This past summer life got busy for a while and I didn't fly for several months. Before taking it back up, I had the oil changed and battery replaced. I went for my first flight back, everything was normal from start up through one lap in the pattern. On my second takeoff, I had a partial (most) power loss just after rotation. It wasn't rough, just lost power. Fortunately, it came back after a few seconds and I flew the pattern and landed. While taxiing in, it was smooth and normal. I did a full power run up and everything was normal. I shut down and sumped the tanks again--no water. (the plane has had problems with water in the right tank before, but interestingly not after sitting out for several months.) I was still feeling uneasy about it, so I had the mechanic check it out. He found rust particles in the fuel system and the fuel servo had some rust internally. So, he replaced the fuel servo and divider. 

After installing the servo and divider, he said the plane ran rough and wouldn't make more than 1200 RPM. I wasn't there that day, mechanic suspected there was a problem with the magneto. It's a little overdue for IRAN, so we sent it out. It got the standard service and was returned. Mechanic installed it and said everything was good. I went out last week after getting the good news. I noticed that the mixture control is now EXTREMELY stiff. I don't have a ton of experience, but I've never seen one anywhere close to this hard to move. the plane started fine, but immediately started running rough and then popping (afterfire?). My wife caught a video of it and you can see the flames coming out of the exhaust. Lean/rich didn't seem to change anything. 

Mechanic took another look the next day and said that everything looks ok, that the popping goes away above 1200 RPM and isn't hurting anything. He checked the plugs again (which were just cleaned) and of course they are black. Compressions were all in the high 70s. We spoke this morning and I asked if he had set the idle mixture correctly. Interestingly, he had one run in which the RPM went up 50 at idle cutoff and then on the next run it went up 200 RPM. I asked him to repeat this and make sure it was correct/consistent and see if the problem improved. He called me back an hour later saying that this time he ran it it was running rough and popping again. He noted EGT in #1 cylinder was 900-1100 while the others were all 600-700. Based on this, he *thinks* I have a sticking exhaust valve and *guesses* that it's on #1. He's recommending pulling that cylinder and sending it off for repair or OH. 

Here are my specific questions right now, though I would really appreciate any thoughts that you all have:

1. Is it normal for the mixture control to be so stiff after installing a new fuel servo?

2. It seems exceedingly unlikely to me that the plane would suddenly develop a stuck valve immediately after the other unrelated repairs were done, am I wrong?

3. If the exhaust valve is stuck, I can see where that would cause the afterfiring, but shouldn't the EGT be lower, not higher? And wouldn't the compression be lower on that cylinder? 

I know that's a lot and I really appreciate any advice/insight. 

[cbarry]

This may sound too simplistic, but have the injectors been cleaned? (which could definitely have gummed up after a period of sitting).  I’m not a mechanic, but the stiffness in the mixture could be from a change in the clearance between the muffler shroud and the mixture control cable/arm.

[RideOrFly]

2 minutes ago, cbarry said:

This may sound too simplistic, but have the injectors been cleaned? (which could definitely have gummed up after a period of sitting).  I’m not a mechanic, but the stiffness in the mixture could be from a change in the clearance between the muffler shroud and the mixture control cable/arm.

Good thought, and yes, the injectors were cleaned. 

[201Steve]

Found rust in the fuel system, there are more things in the system than the servo and the divider. I’d probably be following that initial find. 

[Will.iam]

Verify mixture linkage wasn’t connected wrong or kink in the cable going to fuel control. 

[PT20J]

Wow. A lot to unpack here. An engine requires GAS to run (Gas, Air, Spark). Assuming that you did a runup before takeoff and both mags were working, a sudden power loss would not likely be spark because there are two magnetos and it's unlikely (but not impossible since you apparently have the IO-360-A3B6D with the dual magneto) that both would be acting up. At any rate, the mag has been IRANed so that is no longer likely the problem. So, that leaves air and fuel. Since the intake ducting would have been removed to replace the servo and nothing was reported found blocking airflow, it was gas. This is also indicated by the fact that you lost power but it didn't run rough which indicates that it was something affecting all cylinders. So, it probably wasn't something as simple as a clogged injector.

The "rust" in the lines is suspicious. There isn't much in the fuel system that can rust. The tanks are aluminum, the lines are aluminum or synthetic rubber. So, the question is what was it, how much was there, where did it come from and is it all gone? Fuel flows through a fine mesh screen in the gascolator before it gets to the servo and the servo has a very fine finger screen at it's inlet. So, it is unlikely (but not impossible) that anything got into the servo internals. It would have been good to flush the fuel system out before replacing the servo. But, that's a done deal now.

If the mixture control is stiff, either something is not right with the servo or the cabling, but something is wrong and your mechanic should have checked and corrected this as part of the installation. The afterfire and black plugs and the fact that it is difficult to adjust the idle mixture all point to a problem with the servo. You said the mechanic replaced the servo and flow divider, but you didn't say with new or overhauled or who did the overhaul.

I'm a little confused about the EGT. You said that you don't have an engine monitor, but you reported different EGTs for various cylinders. Do you have a multi-cylinder EGT? An any rate, a stuck exhaust valve will take one cylinder completely out of action and the engine will shake like the dickens and the cylinder with the stuck valve should be cold not hot. I would definitely not pull the cylinder (even if it were a stuck valve, the standard procedure is to ream it on the engine, not remove the jug) and I would investigate the servo installation.

Good luck.

[EricJ]

When I bought my airplane it had a bunch of issues, and we eventually discovered the finger filter in the fuel servo was full of rusty crap.    This was after an injector clogged on takeoff, which prompted close looks at everything.   No, the mixture cable should not be stiff after installing a new servo, and since it would have had to have been disconnected and reconnected during the servo removal it is likely that it wasn't reinstalled correctly.

I would suggest not pulling the cylinder until a flow test is done on the injectors.   If they're flowing the same, and there's borescope or other evidence to indicate the cylinder needs work, then it may be a candidate for removal.   If there was rust in the servo, there's likely crap downstream, too, and even though you had the divider redone I'd still suggest a flow test to rule out the line/injector/nozzle before sending the cylinder away.    OR at least just remove that injector/nozzle assembly and verify that it's clean and unobstructed, and the line as well.   

It is unlikely that the servo and ignition suddenly had problems at the same time, and then the cylinder too.    

[RideOrFly]

10 hours ago, PT20J said:

The afterfire and black plugs and the fact that it is difficult to adjust the idle mixture all point to a problem with the servo. You said the mechanic replaced the servo and flow divider, but you didn't say with new or overhauled or who did the overhaul.

It was replaced with an overhauled unit. I'll have to check and see where it came from. I am going to ask the mechanic to contact them to help troubleshoot, hopefully that will be helpful. I can't see how this isn't the servo at this point.

10 hours ago, PT20J said:

I'm a little confused about the EGT. You said that you don't have an engine monitor, but you reported different EGTs for various cylinders. Do you have a multi-cylinder EGT?An any rate, a stuck exhaust valve will take one cylinder completely out of action and the engine will shake like the dickens and the cylinder with the stuck valve should be cold not hot. I would definitely not pull the cylinder (even if it were a stuck valve, the standard procedure is to ream it on the engine, not remove the jug) and I would investigate the servo installation.

I have a UBG-16, I meant that I don't have one that I can download and analyze. That was my understanding about the valve as well--in addition to not wasting the money pulling the cylinder, I worry about what else will get broken in the process and I'm honestly dumbfounded at the recommendation to pull the cylinder. 

I really appreciate the time you put into this, and for explaining it simply. 

[A64Pilot]

The UBG-16 will tell you everything you need to know.

There is a module that’s easily added that makes it downloadable if you desire. I had one on both mine, never downloaded either though.

I think you need to find another mechanic, anytime you have a problem and diagnose it to be X, you don’t start jumping around all over the place replacing the next part it could be, you can go broke with that mentality and even induce problems, because just because something has been serviced or overhauled is not a guarantee it’s operating correctly.

Just as a guess and remember I’m sitting on my couch and haven’t even seen your airplane I’d be real suspicious of the servo, mostly because it’s stiff, and it shouldn’t be.

Another reason I’d find a different mechanic is this one should have NEVER in my opinion signed off a fuel servo that was stiff, it should move with just about no friction.

A sticking valve is easy to diagnose even with out a monitor, but dead stupid easy if you have one, and in my opinion you have a good one. Not pretty to look at, it’s not big and colorful, but it’s accurate and gives you all the data you need, you don’t need to blow the bank on a different prettier one.

I’ve seen “rust” in fuel be red Georgia clay from a dirt dobbers nest in a vent that was blown out.

If you still have the rust, if it rust it will stick to a magnet. Iron oxide is less magnetic than pure iron, but it’s still magnetic.

[RideOrFly]

9 hours ago, EricJ said:

When I bought my airplane it had a bunch of issues, and we eventually discovered the finger filter in the fuel servo was full of rusty crap.    This was after an injector clogged on takeoff, which prompted close looks at everything.   No, the mixture cable should not be stiff after installing a new servo, and since it would have had to have been disconnected and reconnected during the servo removal it is likely that it wasn't reinstalled correctly.

I would suggest not pulling the cylinder until a flow test is done on the injectors.   If they're flowing the same, and there's borescope or other evidence to indicate the cylinder needs work, then it may be a candidate for removal.   If there was rust in the servo, there's likely crap downstream, too, and even though you had the divider redone I'd still suggest a flow test to rule out the line/injector/nozzle before sending the cylinder away.    OR at least just remove that injector/nozzle assembly and verify that it's clean and unobstructed, and the line as well.   

It is unlikely that the servo and ignition suddenly had problems at the same time, and then the cylinder too.    

Much appreciated. I'm going to ask them to do a fuel flow test today and see what the results look like. Also going to ask them to check the mixture control installation--the mechanic assured me yesterday that it was "within limits", but I'm not aware of a specific limit that would apply and I've never flown anything that was that hard to move. 

[A64Pilot]

A lot of this I believe your allowed to do yourself, like the fuel flow test I believe.

However I’m not real up on what a pilot can do as I’ve had my A&P before I got my civilian airplane license.

You’re not allowed to change servos, cylinders etc of course unless under supervision at least, but you can very often troubleshoot it to the part.

That in my opinion is the biggest use of a monitor, maintenance troubleshooting.

[RideOrFly]

16 minutes ago, A64Pilot said:

The UBG-16 will tell you everything you need to know.

There is a module that’s easily added that makes it downloadable if you desire. I had one on both mine, never downloaded either though.

I did not know that. It actually occurred to me that I'd be better off putting in a newer engine monitor before doing anything else just to help with diagnostics. Will have to check into the module for the UBG. 

16 minutes ago, A64Pilot said:

I think you need to find another mechanic, anytime you have a problem and diagnose it to be X, you don’t start jumping around all over the place replacing the next part it could be, you can go broke with that mentality and even induce problems, because just because something has been serviced or overhauled is not a guarantee it’s operating correctly.

I agree 100%. There are two shops on the field and I gave up on the other one after they took a similar approach to an electrical problem last year. Unfortunately, I'm kind of stuck with this for now since the plane can't move. Unless competent mechanic would travel--I'd rather pay for expertise than unnecessary repairs. 

[A64Pilot]

Call EI, the UBG has been discontinued but they may still support it.

I believe the CGR-30 is an easy upgrade if you feel you must. I think but do not know but it may be an almost plug and play, if so it will save big $$ on install, and I believe it fits in the same hole.

Again, call EI they are very helpful. I have worked with them pretty extensively in the past.

https://iflyei.com/contact-support/

https://iflyei.com/upgrade-packages/

[PT20J]

Here is the RSA fuel injection troubleshooting guide.

RSA Troubleshooting.pdf

[RideOrFly]

1 hour ago, PT20J said:

Here is the RSA fuel injection troubleshooting guide.

RSA Troubleshooting.pdf 783.56 kB · 0 downloads

Absolutely loving that paragraph "the art of troubleshooting." I'm going up tomorrow to spend a few hours and will bring this along. I spoke with the rep from QAA earlier today (they sold the overhauled servo) who offered to help troubleshoot over the phone and even to get the Precision Airmotive folks involved if needed. Very helpful.

[EricJ]

4 minutes ago, RideOrFly said:

Absolutely loving that paragraph "the art of troubleshooting." I'm going up tomorrow to spend a few hours and will bring this along. I spoke with the rep from QAA earlier today (they sold the overhauled servo) who offered to help troubleshoot over the phone and even to get the Precision Airmotive folks involved if needed. Very helpful.

That's a very good plan.   Disconnecting the mixture cable from the servo will tell right away whether the stiffness is due to the servo or the cable.   I'd be surprised if it's the servo.

 

[Ragsf15e]

Could he also have the “secret” fuel screen after a Dukes fuel pump or did the Js never have those?  Might be another place to look for junk in the fuel system.

[Ragsf15e]

Just to expound on that, there was an AD some Dukes electrical fuel pumps that had plastic vanes which could come apart.  A filter was inserted right after the pump to catch pieces.  Im not saying your fuel pump came apart, but if there’s an inline filter after your electric boost pump, it’s another place to look.  You have to remove the belly panel immediately behind the pilot side cowl flap (concave panel shape).

Edited January 23 by Ragsf15e

[RideOrFly]

12 minutes ago, Ragsf15e said:

Just to expound on that, there was an AD some Dukes electrical fuel pumps that had plastic vanes which could come apart.  A filter was inserted right after the pump to catch pieces.  Im not saying your fuel pump came apart, but if there’s an inline filter after your electric boost pump, it’s another place to look.  You have to remove the belly panel immediately behind the pilot side cowl flap (concave panel shape).

Thank you...I had read about that a while back so I'll take a look in the morning to see if it's installed. If I'm remembering correctly, the AD log said "NA" next to that one, so maybe it didn't have the Dukes pump.

The more I think about this whole thing, the more I think that maybe just some water was sitting somewhere in the system that I couldn't sump it which led to the original power loss. That's exactly how it acted when I lost power. It seems like everything since then has been iatrogenic failures.  

[Ragsf15e]

9 minutes ago, RideOrFly said:

Thank you...I had read about that a while back so I'll take a look in the morning to see if it's installed. If I'm remembering correctly, the AD log said "NA" next to that one, so maybe it didn't have the Dukes pump.

The more I think about this whole thing, the more I think that maybe just some water was sitting somewhere in the system that I couldn't sump it which led to the original power loss. That's exactly how it acted when I lost power. It seems like everything since then has been iatrogenic failures.  

I tend to agree with you. Maintenance is funny on these things. Sometimes you break two more things trying to fix one.  Maybe even one that wasn’t broken….

[RideOrFly]

1 hour ago, EricJ said:

Disconnecting the mixture cable from the servo will tell right away whether the stiffness is due to the servo or the cable.

 

Item #1 on the agenda.

[KSMooniac]

5 hours ago, RideOrFly said:

Absolutely loving that paragraph "the art of troubleshooting." I'm going up tomorrow to spend a few hours and will bring this along. I spoke with the rep from QAA earlier today (they sold the overhauled servo) who offered to help troubleshoot over the phone and even to get the Precision Airmotive folks involved if needed. Very helpful.

That might be part of the problem too.  Sometimes they are quality-free, so don't assume they gave you a good product.

[RideOrFly]

18 minutes ago, KSMooniac said:

That might be part of the problem too.  Sometimes they are quality-free, so don't assume they gave you a good product.

I’ve heard that from several sources now, including the shop owner—AFTER he had ordered the servo and had my mag overhauled there. *bangs head against wall*

[blaine beaven]

When I read about your initial power loss it reminds me of a situation I had where I had flown somewhere in the morning, the plane sat in the sun all day, I refueled - but not filled - in the hot afternoon. On the flight home climbed up high and had some bumps (hot summer day). About a minute after I put the nose down to decend, there was a change in sound and power output that lasted about 5 seconds.
 

I spent some money chasing this phantom. Checked fuel injectors, spark plugs, valve clearances, scoped cylinders etc.  The best explanation I received was from the owner of an engine rebuild shop. He said that flying home likely washed the condensation off the walls and ceiling of the tank into the fuel, they took time to condense, it settled into the low point, and when I put the nose down to descend it sucked in some water. 
 

His advice was that if I’m fuelling, fuel earlier in the day, shake the wings and let it rest for 10 or so minutes before sumping. 
 

On the topic of the stiff mixture cable, I had the same problem at another time, and it was a fuel servo that was failing. Confirmed that by disconnecting mixture cable and then it moved smoothly. The arm on the fuel servo it connected to did not move smoothly, and was indicative of further internal failures. 
 

Good luck!

[Shadrach]

6 hours ago, blaine beaven said:

When I read about your initial power loss it reminds me of a situation I had where I had flown somewhere in the morning, the plane sat in the sun all day, I refueled - but not filled - in the hot afternoon. On the flight home climbed up high and had some bumps (hot summer day). About a minute after I put the nose down to decend, there was a change in sound and power output that lasted about 5 seconds.
 

I spent some money chasing this phantom. Checked fuel injectors, spark plugs, valve clearances, scoped cylinders etc.  The best explanation I received was from the owner of an engine rebuild shop. He said that flying home likely washed the condensation off the walls and ceiling of the tank into the fuel, they took time to condense, it settled into the low point, and when I put the nose down to descend it sucked in some water. 
 

His advice was that if I’m fuelling, fuel earlier in the day, shake the wings and let it rest for 10 or so minutes before sumping. 
 

On the topic of the stiff mixture cable, I had the same problem at another time, and it was a fuel servo that was failing. Confirmed that by disconnecting mixture cable and then it moved smoothly. The arm on the fuel servo it connected to did not move smoothly, and was indicative of further internal failures. 
 

Good luck!

Sometimes it’s good to have an explanation even if it’s a bit of a long shot. The fuel pick ups are about a 1.5” above the tanks low point near the aft tank wall. For the scenario you were given to happen, the tank would need a pretty significant amount of water to displace the 2.5gals of unusable fuel and flow upward to the fuel pick ups while in the nose down position.