Intermittent Rough Running Engine on Climb

[DRJ78]

Hey Guys. Got a 78 201J Model. Engine has about 400 hours on it. On climbs it will run rough from time to time. When it does if I level off and enrichen the mixture it will smooth out. I only have CHT on one cylinder. In climbs it will generally hover around 360. It did it once 10 hours ago then went away. Did it again just the other day. Had our A&P boroscope the cylinders and perform a compression check. All cylinders were over 75/80 and cylinder walls looked great. Airplane had brand new spark plugs, ignition harness, and magnetos put on it last annual.

Any idea what this could be? I know it's rare to get detonation on a non turbo engine. Cowl flaps open and again CHT is around 360.

I'm in North Carolina. Any recommended service centers within 300 miles or so that can solve this issue? My longtime A&P recently retired and I'd like to find someone to solve this issue as I don't feel comfortable flying it until it's fixed.

 

Thanks.

[Oldguy]

Might look at @AGL Aviation. They are active on here and have had several of their customers give PIREPs on their service - always good responses.

[ArtVandelay]

I’m confused, you say when you level out and enrich the mixture it runs smoothly again? Why not enrich on the climb? What’s your fuel flow rates?

Here is where a engine monitor would be helpful.

 Did you try switching tanks? Turn on the electric fuel pump? Doing a mag check?

 

Tom

 

 

[gsxrpilot]

What @Oldguy said. Go to Morgantown, NC.

[DXB]

Seems like a pretty broad differential for a skilled A&P to sort out. Could be fuel (e.g. partially plugged injector) or spark (seems less likely with new plugs, harness, mags but not impossible). This is basic engine work - you don't need a Mooney Service Center for it.  Borescope and compressions were unlikely to give insight here, and it would not have been my first thought to do those checks. I'm sure someone will say it, but this problem would be MUCH easier to diagnose with a data-logging engine monitor in place.

[bbailey]

I had a Citabria get rough sometimes on takeoff and climb. Finally the third shop found a inner valve spring broken.

Bruce

[DRJ78]

It ran rough enough my first assumption was some sort of detonation and I wanted to end it as quickly as I could so I leveled off for air flow.

I'll add some more context. The last time it did it was on takeoff from KMRH. Full rich mixture. Ran rough. Leveled off and reduced power. This was at 1200 feet. Smoothed out. 

I do not have a fuel flow gauge. 

I agree an engine monitor would be great and has been on the agenda for last year or so. $4,000 in re-doing the ignition system ate into that budget earlier in the year and now 

Further background. The first time it did it was I initiated a climb from about 2000 feet and forgot cowl flaps. Ran rough, leveled off, opened cowl flaps. Smoothed out. That was when I had him boroscope and do a compression check. Unfortunately I did not get a CHT that time. Since then when it has done it the CHT has been around 360.

[DRJ78]

GRJ and GSXR thank you for recommendation.

[kris_adams]

14 minutes ago, DXB said:

Seems like a pretty broad differential for a skilled A&P to sort out. Could be fuel (e.g. partially plugged injector) or spark (seems less likely with new plugs, harness, mags but not impossible). This is basic engine work - you don't need a Mooney Service Center for it.  Borescope and compressions were unlikely to give insight here, and it would not have been my first thought to do those checks. I'm sure someone will say it, but this problem would be MUCH easier to diagnose with a data-logging engine monitor in place.

^^This...could be anything really.  Here's my engine miss story...

I had a super intermittent miss years ago.  Turned out the fuel tank sealant was "flaking" off and just enough would get by or through the fuel screen in my '79J model and would plug injector for a brief amount of time...long enough to freak me out though.  Fixed the tanks and not one miss since then.  And if anyone asks...I don't really understand the screen/filter setup on my J model but the engine shop (Gann Performance Engines) was definitely able to show me crap out of the injectors that looked like tank sealant.

[Bob - S50]

Have you had the plane for awhile or is it new to you?

If it usually only happens during climbs, that could be due to either the pitch attitude or high power setting.

Is it always the same tank or does it happen on either tank?  If just one tank, maybe there is something loose in the tank that partially covers the fuel intake line at high pitch attitudes.

Morning sickness?  Do you always taxi around at full rich?  Do you use ROP settings at cruise?  What power settings (MP & RPM) do you use and what fuel use rate do you use for fuel consumption calculations?  Is it pretty accurate?  Does the problem only happen during the first 20 minutes or so of flight?

[Bob - S50]

5 minutes ago, Kris_Adams said:

^^This...could be anything really.  Here's my engine miss story...

I had a super intermittent miss years ago.  Turned out the fuel tank sealant was "flaking" off and just enough would get by or through the fuel screen in my '79J model and would plug injector for a brief amount of time...long enough to freak me out though.  Fixed the tanks and not one miss since then.  And if anyone asks...I don't really understand the screen/filter setup on my J model but the engine shop (Gann Performance Engines) was definitely able to show me crap out of the injectors that looked like tank sealant.

We had a similar problem with our plane when we got it.  Engine had about 400 hours on it.  It turned out to be two problems.

1.  Morning sickness.

2.  Red/orange junk in the fuel lines.  Just about plugged up the fuel pump intake filter screen.  Occasionally some of it would get past the filter and plug an injector.  Took about 100 hours of flying to work all that crap out of the system.

We had the valve guides reamed and we now religiously taxi with the engine leaned until it will barely run smoothly, and cruise LOP.  The engine now has 1600 hours on it and we haven't had any more problems.

[DRJ78]

I've put 350 hours on the plane. I normally climb at 100 MPH at 2500 RPM and Full throttle. At cruise I'll generally run 25 Squared. 

I lean slightly on the ground but possibly not aggressively enough. 

What is morning sickness...?

 

[Yetti]

Do a leak down test on the mech fuel pump.   Clean the strainer on the tank selector, and the fuel filter next to the elec pump.   Clean the filter on the fuel servo.   Do a baby jar test.   Assuming your Fuel Servo and divider were OH with the engine.

[Andy95W]

Do the easy/cheap stuff first- clean and gap the spark plugs, clean the fuel injectors, clean all fuel screens.  Make sure the induction tubes are all secured and tight.

[DRJ78]

Yes it does only happen in the first 20 minutes or so of flight it seems. I have not noted which fuel tank. I will do that next. I use ROP settings at cruise. I tend to get around 10.5 GPH to the best of my calculations on fuel flow at those settings. I will not commit to that being 100 percent accurate.

Edited November 14, 2019 by DRJ78

[Andy95W]

Just now, DRJ78 said:

 

What is morning sickness...?

 

A sticking exhaust valve.  Not normally an issue after the engine is warmed up.

[Bob - S50]

2 hours ago, DRJ78 said:

I've put 350 hours on the plane. I normally climb at 100 MPH at 2500 RPM and Full throttle. At cruise I'll generally run 25 Squared. 

I lean slightly on the ground but possibly not aggressively enough. 

What is morning sickness...?

 

Since you said the problem happens during the climb, it might be your RPM.  Mine is also a '78J.  It has the IO-360-A3B6D engine.  That's timed at 25 BTDC.  That puts peak pressure closer to TDC than planes with two mags timed at 20 BTDC.  By using 2500 RPM in the climb you are pushing peak pressure even closer to TDC.  When you level off and pull the throttle back that reduces MP which moves peak pressure away from TDC.  It also reduces the amount of pressure generated which further reduces stress on the engine.

Try doing a few climbs at 2700 RPM and see if that helps.  Use full rich (unless you live significantly above sea level) and full throttle for takeoff.  Without an engine monitor, leave it that way for at leave a few thousand feet of climb.

On the ground, set 1000 RPM then lean until the engine starts to stumble just a little, then enrichen just enough to make it run smoothly.  If you did it right you won't be able to do a magneto check without enriching the mixture.

 

[gsxrpilot]

I'm in agreement here with @Bob - S50. The only reason to back off the RPM in the climb is for cooling. Some Mooneys can run hot in the climb even at full rich mixture and reducing the RPM just a bit, e.g. 2650, can help with cooling. But the vast majority of us climb at full RPM all the way to altitude. 

I would also mention that 25 squared is a bit of an outdated practice as well. While 2500 RPM is not unusual, most typically run full throttle in cruise. There are exceptions to this especially when running at relatively low altitudes, such as below 5000 ft.

As Bob says, this might just be from the way you're running the engine. Having said that, since you're in NC, it would still be worth a quick flight over to Morgantown to meet Lynn at AGL. You're gonna need a good Mooney shop sooner or later, and he's the best in your area.

[ArtVandelay]

I’m not sure lower RPMs help cooling, I would think higher is better, lower RPMs do help noise reduction. I’m assuming engine efficiency doesn’t change much between 2500-2700 range.


Tom

[EricJ]

I'll +1 for a partially clogged injector nozzle.    Could be other things, but that seems to stick out for me.

It's pretty easy to pop the nozzles off and clean them.   Would be simple to eliminate that as a possibility.

 

[DRJ78]

Appreciate everyones feedback. I contacted Lynn and will be having him complete an annual and seeing if he can determine the issue. I'll follow up and let everyone know what it turned out to be.

[PT20J]

A '78J is a great machine - I used to own one. Don't feel bad about not having an engine monitor. A lot of folks here have them and have learned to use them to advantage. But, it's only another tool: Remember good mechanics diagnosed and fixed airplanes perfectly well before these things became common. It just takes a little longer.

The J should climb fine full rich, cowl flaps open, 2700 rpm, full throttle. It won't be anywhere near detonation under these conditions.

Engine roughness is caused by uneven power from the cylinders. The little Lycoming 4 banger only has four to begin with, each contributing 50 bhp at takeoff, so if one isn't pulling it's weight, you feel it. Assuming that the compression is good and the valves aren't burned (I assume the valves were checked with the borescope along with the cylinder walls) then it must be fuel, ignition or valve action. I'd clean the injectors, test the plug resistance and clean and gap them, and look over the ignition harness. If it's not fuel or ignition, it could be the valve action. Your mechanic can do a wobble test, measure valve lift and check the valve springs pretty easily and noninvasively. The thing to do is be methodical and through and check the simple things first.

Skip

 

 

[Ragsf15e]

This has nothing to do with your roughness, but others are giving tips (good ones) on climb power settings and mixture... do you really climb at 100mph as you said or is that kts?  I have an F, so not exactly the same, but I thought it was pretty normal to climb at 110-120 mph or so.  You will notice better visibility, lower chts, and likely be more efficient... we have a research paper around here on climb speeds...  I think most efficient for a long flight in the paper is like 1.4 x Vy.  

I would use Vy or Vx as appropriate until at a safe altitude, then accelerate to your chosen cruise climb speed.  Mine is 120mph.

Edited November 15, 2019 by Ragsf15e

[gsxrpilot]

8 hours ago, ArtVandelay said:

I’m not sure lower RPMs help cooling, I would think higher is better, lower RPMs do help noise reduction. I’m assuming engine efficiency doesn’t change much between 2500-2700 range.

It most certainly helped cooling in my M20C. A reduction of even just 50 RPM made a difference in the climb and would bring the hottest cylinder down from about 405 to 380. 

Fewer explosions per minute? Made sense to me. Now the 252 is very well cooled. I can climb at full throttle, full RPM, and full rich, from sea level to FL260 and never reach 360 on any cylinder.

[carusoam]

Congrats on your first post, BB!

Welcome aboard, DRJ!

Couldn’t we have started with something easier like... a pic in today’s flight... 

1) It helps to have lots of instruments... but we get what we get, and we don’t get upset...

2) be on the look out for various weirdnesses...

3) leveling off causing the challenge... is interesting...

4) Some people have reported...

• air leaking into the fuel system... blue stains leaking out...
• fuel pressure can change some with attitude... more of a carb / lower FP issue...
• mixture can help define the problem /better or worse when mixture is adjusted?
• adding the electric fuel pump can help define the problem / better or no change with the electric pump?
• changing tanks... better or worse?
• Anything in the sump drains?
• Any idea what your FF is in any condition? Timing fuel used from one tank during cruise...
• Any idea how well your baffling is set up?
• Excess heat can cause a bunch of challenges...
• having noticeable pre-ignition... probably won’t fix itself and behave normally for very long... not under high power climb conditions..
• partially blocked fuel injectors
• a bad plug

5) +1 visiting Lynn at AGL

PP thoughts only, just collected some ideas around MS...

Best regards and good luck with your next steps...

Got any pics? Any data?

Best regards,

-a-