Help Diagnose Engine Problem - M20K TSIO-360-MB

[Z W]

Hello friends,

I could use some help from the braintrust.  Plane has been in the shop essentially since annual in June.  1982 M20K 231 with the "262" conversion, so a TSIO-360-MB1 engine with fully automatic wastegate.  Facts go like this:

Plane goes into annual operating fine.  Two cylinders (#3 and #5) showed low compressions.  A&P recommended and we tried lapping the valves in place.  Also did some tank re-sealing work.  Annual completed and signed off.

Valve lapping worked on the #5 cylinder, but first flights post-annual had abnormally high CHT's in the #3 cylinder.  Could not keep it under 400 degrees at climb power, and the engine started to run rough as soon as we leaned it off of full rich.  CHTs did decrease with reduced power.  Other than those issues plane ran normally.

Ordered a new #3 cylinder.  After installation, CHTs were nice and cool and even.  However, the engine will no longer make max power.  It should produce 36" of MAP.  Instead, it produced only 34" MAP on the first test flight.  I did not notice that until I was already flying (shame on me), but came back around and landed no problem.  Otherwise the plane ran normal.

Since then the shop has been chasing this problem.  Hooked up a shop vac to the intake to look for intake manifold leaks.  Found some, replaced all old hoses, no change in MAP.  Suspected fuel line contamination from the tank reseal job.  Checked all lines, supposedly clear.  Checked fuel pump.  I was told it was not making proper pressures or flows.  Just got a new one.  

The IA/A&P running this small shop left recently.  We now have a new IA in charge.  They are struggling with this.  They put the new fuel pump on and supposedly it's set for pressures and flows (have not been down to double-check).  He says today it will only make 2500 RPM and 32" MAP during runup.  He said we probably need to go fly it to see if the engine makes full power while moving.  I told him this engine always makes full power standing on the brakes.  In fact, it will sometimes overboost to 38" or so MAP, then the wastegate will open and it settles at 36".  He was going to go try a high-speed taxi test this afternoon to see if it will make full power on the runway.  I do not think it will.

What else should we check?  Plane has been down for four months at this point.  Would appreciate any ideas as to how a changed cylinder can result in loss of MAP.  I suspect something else was removed and reinstalled incorrectly but don't know where to look.

Thanks in advance.

[231MJ]

I have same conversion and same engine.  This sounds frustrating.  I once chased a rough running engine after a top overhaul - after spending a lot of money we checked the simplest thing...one injector was blocked.  Cleaned it and it ran great.  A rebuilt fuel pump is expensive, and I wish I had not done it but sometimes we get so desperate to fix an issue we get carried away.  Make sure they check the simple stuff first - all of it.  

[Z W]

Injectors were checked with the fuel lines.  All supposed to be OK.  Good thought though.

[Jetrn]

Your fuel setup was done incorrectly after replacing the fuel pump. You are not getting enough fuel at high power. The fuel setup calls for 700rpm with an unmetered fuel low pressure of 6.25-6.75 but should be set closer to 6.25.(low pressure screw on fuel pump). It’s a little easier to set the high flow using the fuel flow gauge in the plane if it reads gph. The book calls for the high flow adjustment to be 28-32psi at full power or 21.3-23gph reach full power. Most would recommend to run this engine with higher fuel flows than book. I run mine at 26.5-27gph. I used a pressure gauge to adjust the lower pressure circuit and used the JPI to adjust the high pressure circuit.

[carusoam]

1) Do you have a JPI 900? Or similar?

2) Do you have an A&P trained in Continental engines?

3) Did last A&P use the proper Continental tools and procedures to measure the compression?

4) It would really suck to find out somebody made decisions based on hard to obtain compressions…

5) Fuel system set-up for the M20K is the most complex of all the Mooneys…. Make sure you know what procedures they are using… and they are being followed by the letter…

 

PP thoughts only, about stuff I have read around here…

See if @jlunseth and @M20Doc are cruising by…

Best regards,

-a-

[Z W]

Thank you for the suggestions on the fuel pump setup.  Will look into that.

We have a G500Txi with engine logging and a Savvy account.  I can post whatever might be helpful.  The first A&P who did the annual had all the proper Continental books/tools and seemed to know what he was doing.  His departure in the middle of the problem has made things challenging.  Apparently several planes were left in various states of stuck on the ground, ours being one of them.  We were confused why everything was taking so long and nobody was responding, then found out he was leaving.  New A&P is walking into a bit of a mess and has his hands full.  Shop owner is great and responsive, not mad about anything, just hoping to find some help here to get our bird back in the air.

Most recent log of MAP/FF demonstrating the problem.  This was before the fuel pump was replaced:

 

 

 

[Z W]

Same flight, but showing MAP/RPM.  Plane was making proper RPM:

[Z W]

Last "normal" flight before the cylinder replacement work when all this started.  Shows MAP at the proper 36" and fuel flows around 25 GPH:

Edited October 18, 2022 by Z W

[jlunseth]

It’s definitely a puzzle. One strong possibility is fuel line contamination, and I know your A&P has supposedly checked that. But if some debris was dislodged during the tank work and got into the fuel system it could explain most of what you are seeing. My first reaction to the hot #3 after the valve relap is a plugged injector, possibly caused by debris, that would cause the cylinder to run very lean. That certainly seems to be supported by the fact that the cylinder would become rough if leaned off full rich. Changing the cylinder itself may have done nothing, except that the injector was removed in the process and probably cleaned, so sure, the new cylinder now runs fine. 

Same thing with the need to replace the fuel pump. Nothing wrong with the pump before the reseal I assume, so why did it need to be replaced unless it also got compromised by some debris.

I know you checked the lines, but don’t forget the gascolator. I seem to remember an incident where a bit of shop rag got into the gascolator and brought the plane down. Since it is a switch, it could be that it plugs in one position and less or not at all in another.

I would make sure that every screen or filter in the fuel system has been checked and cleaned or replaced, and it may be worthwhile to drain the tanks and make sure there is nothing swimming around. If there is, then you are going to continue to see one problem after another pop up as the debris finds a new place to stop and muck things up.

One question. You mention a result of 2500 and 32”. Is 2500 the max RPM on the 262? Or was the engine not making max RPM. If the prop governor was set too low then the engine may not be able to get to full power.

[Will.iam]

Also just because your fuel pump is overhauled and bench tested does not mean it’s setup right for your installed application. I had my fuel pump, spider, throttle body all IRAN and bench tested as a group together setup. The A&P said they are very good at getting right and it would be plug and play. Well it wasn’t. Right off the bat t/o power was at 21 gph way too low. Had to adjust that back up to 25 gph. And the low pressure circuit was at 3.1 so had to increase that to 6.1. Then mixture was so rich i got a 1200 rpm rise to cutoff. Adjusted that to 50 rpm rise. Then went back through and verify T/o ff was 24.7 so I didn’t change that and low pressure circuit was still 6.1 good enough for me and besides being in spec the engine now idled beautifully like a new engine at 650rpm. So much for the shop getting the setting right. In hindsight i wonder if the shop set it for an LB instead of an MB engine as it was just so far off initially. 

[A64Pilot]

I don’t know the Savvy charts, but if your not getting boost it’s most often one of two things.

1. you have some kind of leak, on either side of the turbo, wastegate opening too soon or cracked exhaust or an induction leak.

2. Your not flowing enough fuel to make enough heat to drive the turbo to high boost.

I would concentrate on fuel and if you get her running well, I’d still take to someone who specializes in setting up Continental fuel flows and have them go through every step one step can effect another, mechanics tend to have specialties, go find a Conti fuel specialist. This is from my understanding very important to get right and you may think you have it right but run into issues at high altitude etc because it’s not right, it’s good enough for sea level but not up high.

Most mechanics won’t even have the calibrated special gauges and fittings etc to do it

 

[Z W]

2 hours ago, jlunseth said:

One question. You mention a result of 2500 and 32”. Is 2500 the max RPM on the 262? Or was the engine not making max RPM. If the prop governor was set too low then the engine may not be able to get to full power.

2700 is redline RPM.  The first report I had of RPM trouble was verbally on the phone yesterday when he said it would only do 2500 RPM and 32" MAP with the newly-installed and newly-adjusted fuel pump.  I have not been by to verify myself yet.  Previously it was doing 2700 RPM but only 34" MAP.

Thanks for all the thoughts and input, it is very helpful.  I was thinking it had to be a turbo/wastegate issue but now you've got me back on the idea that it could be fuel contamination or  blockage.  Supposedly all screens were checked from the tanks to the cylinders before we replaced the fuel pump (which we could not find any record of ever having been repaired or replaced in the logs). I'm going to make sure it is flowing 25+ GPH on the fuel flow gauge.

We did check the #3 injector before replacing the cylinder.  Lean condition was my first thought as well but when it checked out OK we just replaced it.  This is a higher-time and, until now, strong running motor that has served us well.  

[Z W]

Today's test run data below.  Thanks to some of the advice above, I was able to locate the Engine Setup Procedure part of the factory service manual with details on how to set up the fuel pump and send it off to the new A&P.  He's going to work through that.  They also put some mousemilk on the wastegate and suspect that could be the next possible culprit.  Thanks for all of the help and tips, and keep them coming.

[jlunseth]

The reason I asked the RPM limit is that 2500 and 32" does not make any sense if the limit is 2700. We are all familiar with the fact that at a certain MP, probably around 20 or 22" in a turbo, the MP will control RPM rather than the prop governor. That is because you are no longer making enough power for the governor to work, the prop is against the stop and what reduces RPM further is reducing power. But 32" is plenty of MAP to make enough power to run the prop at the redline limit. If you are not making enough power to move the prop off the stop at 32, that is a new one on me. I seriously doubt that the prop is sitting on the stop and the power output is what is controlling engine RPMs in that chart.

Just a wild guess, but in the last chart you posted it looks to me as though the engine was just not run at full power. The RPMs were set to 2463 instead of 2700 and the MP was set to 33-34". It would be very odd if the MAP wee 33-34", the governor was truly set for 2700, but the RPMs were only 2500.

Is it possible that the A&P has adjusted the prop governor so the prop cannot make full RPMs and therefore the engine can't make full HP? Or is the A&P maybe adjusting the fuel flow by running the engine at 2500 or some RPM number less than 2700? If you want to dig into this yourself, you should google SID97-3G (I believe G is the current version). You should also find the STC for the 262 conversion and see if there are any special procedures for setting fuel flow that modify 97-3G. I tried to copy and paste the parameters for you but they could not copy.

 

[Z W]

Cool.  I assume you mean the parameters below? (screenshots work well).  I've sent that document to the A&P.

I do not understand the relationship between RPM, MAP, and FF, to be 100% honest.  I'm pretty handy with cars and boats but know very little about airplane engines.  Trying to learn.  Thanks again.

[Z W]

I do not see any further instructions in the 262 STC that we have.  Another good idea though.

[N231BN]

Today's test run data below.  Thanks to some of the advice above, I was able to locate the Engine Setup Procedure part of the factory service manual with details on how to set up the fuel pump and send it off to the new A&P.  He's going to work through that.  They also put some mousemilk on the wastegate and suspect that could be the next possible culprit.  Thanks for all of the help and tips, and keep them coming.

The bottom graph shows fuel flow and fuel pressure. I'm not sure what the fuel pressure number here is indicating but if it's metered pressure from the flow divider, you have an obstruction there.

At full power the metered pressure should be 13.6-15.3 with a fuel flow of 21.3-23 gph.

If it is indicating unmetered pressure, it is low as the full power range should be 28-32 psi.

20.4 GPH is enough fuel to generate 210 HP ao this is very confusing. The turbo is capable of making full power at FL280 so small leaks won't cause any issues at low altitude. It would be helpful to see a TIT plot as well.

Make sure they are referencing the proper numbers for a -MB and not the original -GB/LB, including the fuel pump P/N.

[N231BN]

The reason I asked the RPM limit is that 2500 and 32" does not make any sense if the limit is 2700. We are all familiar with the fact that at a certain MP, probably around 20 or 22" in a turbo, the MP will control RPM rather than the prop governor. That is because you are no longer making enough power for the governor to work, the prop is against the stop and what reduces RPM further is reducing power. But 32" is plenty of MAP to make enough power to run the prop at the redline limit. If you are not making enough power to move the prop off the stop at 32, that is a new one on me. I seriously doubt that the prop is sitting on the stop and the power output is what is controlling engine RPMs in that chart.
Just a wild guess, but in the last chart you posted it looks to me as though the engine was just not run at full power. The RPMs were set to 2463 instead of 2700 and the MP was set to 33-34". It would be very odd if the MAP wee 33-34", the governor was truly set for 2700, but the RPMs were only 2500.
Is it possible that the A&P has adjusted the prop governor so the prop cannot make full RPMs and therefore the engine can't make full HP? Or is the A&P maybe adjusting the fuel flow by running the engine at 2500 or some RPM number less than 2700? If you want to dig into this yourself, you should google SID97-3G (I believe G is the current version). You should also find the STC for the 262 conversion and see if there are any special procedures for setting fuel flow that modify 97-3G. I tried to copy and paste the parameters for you but they could not copy.
 

That was just a ground run. A properly adjusted propeller won't get full RPM while static, especially at a reduced power setting. The next time you takeoff run the power up to 32" and note the RPM before you release the brakes.

[carusoam]

Z,

Next steps…

1) You have uploaded your engine data to Savvy…

2) You have taken some screen shots… that have generated the next set of questions…

3) Go to savvy, click the share button, then post the link here… 

4) This way, people can run through the data comparing different variables and see what other sensors are being captured….

5) there is a ton of correlation to your previous non-aviation experience…

6) Consider the prop governor to work like a continuous transmission…

7) with low power, the gov is off line… the blades are sitting on their low pressure stops, least resistance to turning… (different if you have a Rocket!)

8) as power comes up, the Governor comes on line…

9) If your prop control is pushed full in… rpm will try to approach 2700…

10) While standing still / static… the prop may get close, but will never make full rpm…. A fast taxi down the runway, may be needed to allow the prop to get there…

11) The graphs above have the important part of the data covered over! 
12) The MAP and the rpm may be climbing together, but a block of data sits on top of the important part of the graph…

13) The MAP tops out, and so did the RPM…

14) you should be able to get a successful run-up… do it slowly, no rush…  the governor should show that it is working properly…  allow enough time to capture data.

 

You have done a lot of work…

Let’s see if you can share the data… to see if there are hints about the next steps should be…

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[Z W]

Well, I'd be happy to send a Savvy sharing link to anyone who wants one in a PM to help diagnose.  As far as I can tell the link is an all-or-nothing, meaning it lets any clicker access our entire uploaded flight history of 478+ flights and never expires until I revoke it, so I don't really want that up on this public forum.  Below is the graph from yesterday's runup without the popup blocking any part of the chart.  I do not know where it's getting the "FUEL_PRESS" data from.  At this point I've determined the new fuel pump was put on without following the engine setup process specified for it in the manual.  Thanks at least in part to Mooneyspace I know the A&P now has the manual on that along with SID97-3G.  That work needs to be done no matter what so I think we're going to let that happen and see how the engine runs after that.  Still open to other suggestions or ideas.  Thanks so much for all the help.

[Fly Boomer]

5 hours ago, Z W said:

Thanks at least in part to Mooneyspace I know the A&P now has the manual on that along with SID97-3G

I think that document has been superseded by M-0.

[carusoam]

The point of sharing the link…

 

1) Is to find out who can help…

Hard to do by invitation in advance…

 

2) Some people that have some skills… may see something quickly

They speak up when they do…. And stay pretty quiet when they don’t…

 

3) Kind of like doctors giving internet advice…. Hard to get, hard to give….

Worst case, some mis-interpretation of the information may occur…

 

4) Possible recommendation… 

Post the link at the top of the thread…

When the thread is done… edit the first post to remove the link…

This will minimize viewing your file 

 

5) I’m not sure everyone has access to all files…

Somebody linked two flights and nothing else the other day…

I wanted to go back another flight or two, but was unable…

 

6) We have a Savvy guy around here… we can always ask him… the best method.

 

PP thoughts only,

Best regards,

-a-

 

 

[Q The Engineer]

It sounds like the fuel system pump and metered pressures aren't right.  One way to check is to look at the fuel flow gauge when you are attempting max power and see if it's hitting the spec shared above of 21.3 to 23 psi.  Also make sure your guys cleaned the injectors, not just looked at them as well as replaced the injector seals.  Hobbs gun parts cleaner works great on the injectors. Carbon will build up on the spray holes causing the spray pattern to be poor leading to poor mixing.  

When your guys are checking the fuel system pressures, they need to measure pump feed pressure for the pump side pressure and metered fuel pressure minus boost (top deck) pressure.  A lot of guys using a differential pressure gauge to measure the metered - boost pressure.  You can also just use two gauges and subtract boost pressure from metered pressure.  I hope you get it sorted soon. 

[Mike A]

Check your fuel spider. I had a similar problem with my -LB and got the spider overhauled and it solved my issues. 

[Z W]

Thanks for the additional ideas.  Plane is still down.  New A&P has ordered and received the gauges required to perform the new fuel pump set up procedure.  They did not come with the proper T's or some other parts required to perform the set up, so those are now on order and supposed to arrive this week.  If getting it properly set up does not solve the problem, we will look at the injectors again, and the fuel spider.