Jump to content

M20J - persistent rough engine troubles


CG Roger

Recommended Posts

I bought a 1977 M20J almost 3 yrs ago.  In the last 2 years, I've had persistent problems with the engine running rough, or not making full power. I don't have an engine monitor, so diagnosing the problem has been very difficult.

Every time it happens, I take it to the shop that I happen to be at - it tends to happen to me while I'm on the road, so unfortunately it hasn't been looked at by the same shop more than once. After each trip to a mechanic, it runs fine for anywhere from 10-30 flt hrs. It's now in the shop for it's 4th visit for what seems to be the same symptoms. Here is what has been done so far, I'm looking to see if anyone has had similar problems, or any suggestions to point the mechanic towards.

Mechanic 1:

- Cleaned spark plugs and replaced magneto and harness

Mechanic 2:

- Replaced spark plugs, cleaned nozzles.

Mechanic 3:

- Cleaned fuel lines, replaced nozzles, overhauled fuel servo

Mechanic 4:

- Checked compressions, checked timing, checked sparked plugs, borescoped exhaust, flow checked nozzles

I'm not a mechanic, and my logbooks are at the shop with the plane right now - so I may be saying things a little incorrectly. But, I think you can get the gist. The current mechanic and the last mechanic seem to be very experienced and have described this as "a real head scratcher". I'm tired of scratching heads, I want to be flying.

I appreciate any thoughts you might have.

-Roger

 

 

Link to comment
Share on other sites

Even a used engine monitor would be better than the current route...

Otherwise you will end up swapping out everything that can go wrong in the lifetime of your engine... Before its time...

1) New plugs might be better than the old ones... but new ones can fail as well...

2) Fuel injectors can get cleaned... sometimes they are Gami(s) and belong in certain cylinders...  not everyone, including each mechanic knows this...

3) to know what’s not working right... run a GAMI spread... see how far one cylinder peaks before the rest...

4) It helps to have a FF instrument to go with that...

Have no fear... I wore those same shoes for a decade... Do the best you can with what you have... acquire an engine monitor as quickly as practical...

Trying to describe an engine with a blocked fuel injector....

Trying to describe an engine with Champion plug challenges...

Trying to describe one mag firing five degrees sooner than the other...

Trying to describe an engine with a sticky valve...

My favorite... trying to diagnose a stuck valve on an O360 during departure without an engine monitor...

If you have data, you can share it...

If you don’t have data, you get a lot of conversation, full of great ideas...

If you don’t know about engine ops and an engine monitor.... you can still recognize when a cylinder goes cold... it will feel like a land straight ahead problem... but realistically, running on three cylinders near sea level, you can get back around through the traffic pattern and land...

Hard to do without an engine monitor...

Is there any resistance to getting an engine monitor, other than time and money?

PP thoughts only, not a mechanic...

Best regards,

-a-

  • Like 1
Link to comment
Share on other sites

If it runs fine for 30 hours, then starts running rough until serviced again, I would suspect sediment in the fuel tanks. Filter the fuel to the engine through a fine white filter. You may have some deterioration some where. 

Engine monitors save a whole lot of shotgunning. 

  • Like 1
Link to comment
Share on other sites

@CG Roger a rough running engine is a specific symptom. Invariably the cause is that the cylinders aren't producing the same amount of power. So you have to look at things that affect one cylinder differently than another. For example things like fuel nozzles and mixture distribution. Not things like magneto that would affect all cylinders. I would look at things like gami spread. Without an engine monitor its difficult but I would start looking at things that affect cylinders specifically. 

Link to comment
Share on other sites

Problem #1

17 hours ago, CG Roger said:

I don't have an engine monitor

Problem #2

17 hours ago, CG Roger said:

it hasn't been looked at by the same shop more than once

Until those two are addressed... it will likely be a long and expensive road to a solution.

  • Like 2
Link to comment
Share on other sites

 Please look at an engine monitor as an investment in the future...when I did mine, my AI installed it on the panel for about 4 hours and he ran the harnesses past the firewall to the engine area...while I knew what to do to finish the installation, your AI could teach you to make up all the wiring connections.  My 830 cost $2,200 (special promotion price). AI 4 hours @$50 and then about another 4 hours of my time, and it was installed and it does a phenomenal job of monitoring just about everything.

knowing what I know now, I wouldn’t own a plane without one

  • Like 2
Link to comment
Share on other sites

FWIW - I just pulled a UGB16 off of my J to install a JPI EDM 900.  Oil Pressure transducer went bad and couldn't find a replacement so I had to STC.  That said, I'd let the UGB 16, along with the probes etc that were on it, go for a very reasonable price if you're interested.  

Link to comment
Share on other sites

I flew an IO-360 for 2 decades in my E-Model, two different engines over that timeframe.  There are two very plausible possibilities.  Easy check - intake tubes; look carefully for cracks, and ensure that the intakes are secure on the engine.  You could have a torn gasket there; look for oil coming down onto the intake tubes.  

That said, the IO-360 is notorious for it's weak link - the fuel servo.  If you have never replaced it, and it has more than 1,000 hours on it, you might want to check there.  The way to see if the fuel servo is starting to fail is to see what sort of RPM rise you get on shut down.  If it rises considerably on shut down as you pull your mixture back, you need to pull the servo and replace it.  A 100+ RPM rise in RPM would be significant as you pull the mixture back to shut down.  If you have a problem getting EGT to rise and maintain a constant temp inflight, that's the fuel servo. 

On the ignition side of things, you want to look at your plugs.  They last about 350 hours, maximum.  Take that into consideration.  You can clean them, gap them, rotate them, bead blast them, but after 350+ hours on an IO-360, you're living on borrowed time.  when was the last time your magnetos were overhauled?  It's suggested every 500 hrs.

Finally, clean your injectors.  That's an easy fix.  If you find that your injector nozzles are worn, you need to replace the injectors.

Remember that there are only 3 elements here to be concerned with - air, spark and fuel.

  • Like 1
Link to comment
Share on other sites

On 10/16/2020 at 6:04 PM, CG Roger said:

I bought a 1977 M20J almost 3 yrs ago.  In the last 2 years, I've had persistent problems with the engine running rough, or not making full power. I don't have an engine monitor, so diagnosing the problem has been very difficult.

Every time it happens, I take it to the shop that I happen to be at - it tends to happen to me while I'm on the road, so unfortunately it hasn't been looked at by the same shop more than once. After each trip to a mechanic, it runs fine for anywhere from 10-30 flt hrs. It's now in the shop for it's 4th visit for what seems to be the same symptoms. Here is what has been done so far, I'm looking to see if anyone has had similar problems, or any suggestions to point the mechanic towards.

Mechanic 1:

- Cleaned spark plugs and replaced magneto and harness

Mechanic 2:

- Replaced spark plugs, cleaned nozzles.

Mechanic 3:

- Cleaned fuel lines, replaced nozzles, overhauled fuel servo

Mechanic 4:

- Checked compressions, checked timing, checked sparked plugs, borescoped exhaust, flow checked nozzles

I'm not a mechanic, and my logbooks are at the shop with the plane right now - so I may be saying things a little incorrectly. But, I think you can get the gist. The current mechanic and the last mechanic seem to be very experienced and have described this as "a real head scratcher". I'm tired of scratching heads, I want to be flying.

I appreciate any thoughts you might have.

-Roger

 

 

You’ve had the fuel, and sparks checked, several times. A few other items to check, the induction pipes have an O ring seal as they enter the intake on the oil sump, they are known to fail.  However I find it hard to believe that would cause a power output issue.

Have you ever pulled the rocker covers and looked at/ compare the lift of the valve rocker arms?

Clarence

Link to comment
Share on other sites

Other symptoms including morning sickness? Wobble test please  

Also look at all your other indications - does  your FF wobble? That can be a symptom of bubbles getting sucked into the line with something as simple as a gascolator O ring. 

if you’re FF testing your injectors, do so with the fuel lines from the spider attached to the injectors.  Test the whole system 

An engine monitor would have likely saved you $$$ on diagnosis and headache at this point.  You would have been able to assess fuel, spark, which cyl is affected, induction leaks, etc  

 

 

 

  • Like 2
Link to comment
Share on other sites

2 minutes ago, bradp said:

Other symptoms including morning sickness? Wobble test please  

Also look at all your other indications - does  your FF wobble? That can be a symptom of bubbles getting sucked into the line with something as simple as a gascolator O ring. 

if you’re FF testing your injectors, do so with the fuel lines from the spider attached to the injectors.  Test the whole system 

An engine monitor would have likely saved you $$$ on diagnosis and headache at this point.  You would have been able to assess fuel, spark, which cyl is affected, induction leaks, etc  

 

 

 

How many hrs? How and where was the engine kept / how often flown before you owned it? Where do you keep it and how often do you fly?  What does not making  full power mean? Not full RPM? How close to book performance on takeoff and in the air?  What’s your oil consumption like? The engine is whispering to you.  

  • Like 1
Link to comment
Share on other sites

Even without an engine monitor, you could collect more info. How rough is rough? Is it short duration or does it continue until you land? Have you ever had it happen and the not taken it to a shop? Maybe it goes away by itself and the things the shops do have no effect.

Roughness can come from something that intermittently affects all cylinders or just one. A mag completely cutting out will cause roughness. Interruptions in fuel flow can cause severe roughness. Milder roughness is caused by uneven power outputs from the cylinders. 

You’ve replaced a lot of fuel and ignition components. I might be looking for a  valve that’s beginning to stick.

Skip

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.