Help troubleshooting engine issue

[FlyDave]

My plane has been down for the last 3 weeks. Here is the problem description:

On initial climb out (80' MSL airport, Throttle/prop/mixture full) and pitched for ~70 KIAS, the engine stumbles (best way I can describe it) and then continues the climb normally. This stumble has such short duration that I don't see anything in the JPI data. Today I tried a flatter/faster climb out 90-100 KIAS and the engine didn't stumble until I pitched up to ~75 KIAS. So it <<seems>> to be when the airplane is pitched closer to Vx speeds when the engine is generating max power.

If I climb to altitude, go full power (throttle/prop & mixture for altitude) and pitch up to 70 KIAS the engine doesn't stumble. So I have ONLY seen this on initial takeoff at full power - and so far at an airport at 80' MSL.

I doubt if this has any bearing on the problem but I moved from the LA basin to Petaluma, CA (o69) in December. The weather has been in the low 30's in Petaluma many nights and the airplane had spent most of it's life in the LA area (10-15 degrees warmer). This stumble problem only started happening after I moved to Petaluma (probably just coincidental).

Mechanic at Petaluma has:

• Inspected fuel system, cleaned injector screens which needed cleaning, verified fuel flow, we flew the plane - no change

• Put hoist on engine and lifted front of the plane to make sure any water in the fuel would run to the sump. I though that when the plane is on the gear on level ground, the sump is the lowest point of the fuel tank - am I wrong?

• Disconnected P-Leads to eliminate master switch and we flew the airplane - no change

• Tested the high tension leads - checked OK but he noted that they were bundled together tighter than an acceptable with zip ties. He re-zip tied some of them but not all.

• I have an oil leak near the back of the engine and the mechanic says the mags have oil on them. He says his next steps would be to remove the mags and check them for oil on the inside. These mags (Slick) were rebuilt ~120 hours ago (500 hr. inspection). He is also suggesting that the wiring harness may need to be replaced.

I'm not thrilled with this mechanic. He isn't concrete in anything he says and makes me kind of nervous!

Any thoughts on this issue are appreciated. I don't want to start bleeding cash with this guy. There is a better shop on the field and I'm probably go to take it to them. They're a bit more expensive but I think I would have been money ahead at this point.

P.S. I miss Mike Passwater at Aircraft Ground Support - my Mechanic at El Monte (KEMT). He has an intuitive feel for troubleshooting and is darn good at it!!

[N601RX]

Is fuel pressure stable when it messes up? Is the boost pump still on? It could be getting a little air in the fuel line from around the fuel selector when at a high pitch. The pump would have to suck harder as the nose comes up higher and if the orings are bad it could let a little air in.

[jetdriven]

That mechanic sounds pretty thorough.  Our fuel selector draws air in on the right tank and it wil stumble when an air bubble goes through the fuel injection. At low altitude and full power in cold weather you are already genrating maximum fuel flow, perhaps 19 GPH.  Try a couple takeoffs with the boost pump on and see if that makes it go away.

[FlyDave]

Boost pump is always on until 1,000' AGL. FF is 19.4 GPH on climb out until 1,000' AGL when I bring it back to 25x25 and lean at 3,000' DA.

This stumble happens before 1,000' AGL.

[FlyDave]

Also, if it was a fuel issue I would think there would be something on the JPI data as I would think a fuel issue would have a longer duration than an electrical issue...but what do I know?

[kmyfm20s]

I had a similar issue as you and ended up rebuilding the mags, it run perfectly now. No oil in the mags but signs of arcing, very little soot marks when the mags where opened up. I use Crown Air in San Diego on my home field, very good Mooney mechanics.

[N201MKTurbo]

I would bet mags also, have you tried doing the climbout on each mag individually?

[1TJ]

My plane has been down for the last 3 weeks. Here is the problem description:

On initial climb out (80' MSL airport, Throttle/prop/mixture full) and pitched for ~70 KIAS, the engine stumbles (best way I can describe it) and then continues the climb normally. This stumble has such short duration that I don't see anything in the JPI data. Today I tried a flatter/faster climb out 90-100 KIAS and the engine didn't stumble until I pitched up to ~75 KIAS. So it <<seems>> to be when the airplane is pitched closer to Vx speeds when the engine is generating max power.

If I climb to altitude, go full power (throttle/prop & mixture for altitude) and pitch up to 70 KIAS the engine doesn't stumble. So I have ONLY seen this on initial takeoff at full power - and so far at an airport at 80' MSL.

I doubt if this has any bearing on the problem but I moved from the LA basin to Petaluma, CA (o69) in December. The weather has been in the low 30's in Petaluma many nights and the airplane had spent most of it's life in the LA area (10-15 degrees warmer). This stumble problem only started happening after I moved to Petaluma (probably just coincidental).

Mechanic at Petaluma has:

• Inspected fuel system, cleaned injector screens which needed cleaning, verified fuel flow, we flew the plane - no change
• Put hoist on engine and lifted front of the plane to make sure any water in the fuel would run to the sump. I though that when the plane is on the gear on level ground, the sump is the lowest point of the fuel tank - am I wrong?
• Disconnected P-Leads to eliminate master switch and we flew the airplane - no change
• Tested the high tension leads - checked OK but he noted that they were bundled together tighter than an acceptable with zip ties. He re-zip tied some of them but not all.
• I have an oil leak near the back of the engine and the mechanic says the mags have oil on them. He says his next steps would be to remove the mags and check them for oil on the inside. These mags (Slick) were rebuilt ~120 hours ago (500 hr. inspection). He is also suggesting that the wiring harness may need to be replaced.

I'm not thrilled with this mechanic. He isn't concrete in anything he says and makes me kind of nervous!

Any thoughts on this issue are appreciated. I don't want to start bleeding cash with this guy. There is a better shop on the field and I'm probably go to take it to them. They're a bit more expensive but I think I would have been money ahead at this point.

P.S. I miss Mike Passwater at Aircraft Ground Support - my Mechanic at El Monte (KEMT). He has an intuitive feel for troubleshooting and is darn good at it!!

Are you using Champion spark plugs? If so get rid of them.

 

Ed

[FlyDave]

No Champs. I switched to Tempest about 100 hours ago. My old Champs had 530 hours on them and were an open circuit when tested with an ohm meter.

[FlyDave]

Bump....

Anyone else have input on this problem?

 

Thanks,

 

Dave

[Marauder]

It does sound like the mechanic is hitting on the most obvious possible causes. His approach may be different from what you are used to, but troubleshooting these kind of problems can be difficult. It's not like you have an obvious broken component he can see. Intermittent stumbling as you described can be a few things. If you have oil on your mags, it would be a logical place to look. The airspeed relationship thing may be just coincidental. Fuel is another possible concern. Trapped water can show up anytime. If you are fuel injected, the injection system is another possible culprit. Sometimes it is just a process of elimination.

[BigTex]

You might be looking at a couple of issues. I had oil on my mags and it turned out to a leaky front seal. You might want to look at that for the oil leak... It may or may not be related to your engine stumble.

[RangerJim]

You might consider discussing your problem with MSC experts at LASAR and/or Top Gun, two fine shops that are relatively close to Petaluma in Lakeport and Stockton respectively.  Having said that, I have to agree that your local mechanic seems to be proceeding in a logical fashion on a thorny troubleshooting problem.  FlyDave's suggestion to try a set of Tempest plugs would be next on my approach to the problem.  Even if plugs aren't the problem it will be money well spent in the long run.

 

If the Tempest plugs don't solve the problem you might consider calling Mike at LASAR, (707) 263-5193, and be prepared to forward him your write up of the issue for consideration.  My M20C has gone through two annuals at LASAR and I am very pleased with the results.  I don't have personal experience with Top Gun but they are also favorably reviewed on this site.

 

Good luck,

Jim Rosser

N3992N

[RangerJim]

I see now that you already have the Tempest plugs.  Sorry for the confusion on my part.

[jetdriven]

Look inside that flow divider for trash which could restrict a fuel injector.

[mooney17n]

Just went thru same issue. E-gap on both mags way off. Had just had them overhauled like u w/in 50 hrs. Reset gap and no issues since. Real easy and quick to do. A&P should have tool to measure angle and set gap.

Good luck!!!!!

[FlyDave]

Great - Thanks all.

Mooney17N - the next step was to pull the mags and open them up. We'll definitely check the E-gap on both mags. Thanks!

[larryb]

Any update?

[FlyDave]

No update. Family illness this week so I will probably get to it next week.

I'll post when I have the issue resolved - or have additional questions for the group.

[takair]

Dave

This stumble, can you feel any loss of power or roughness? If not, is a noise? Is it possible that there is a rumble related to a certain AOA and airflow? Are all of your cowl fasteners secure, nose gear doors tight, etc?

[Alan Fox]

Any possibility the fuel line to the transducer is bent at too deep a radius? Had this problem when I installed my JPI....

[FlyDave]

Rob,

 

It definitely feels like the engine misses but it is of such short duration that there is no loss of power and no change indicated on the JPI or it's downloaded data.

 

Dave

[dsking001]

I had a similar experience with my M20J. Shortly after takeoff the engine seemed to have a momentary hiccup. It turned out to be a mag failing. This was never detected on a normal pre-takeoff run-up. I had several mechanics, even from a mooney service station, fly the plane to see if they noticed anything. It took several months to diagnose the problem. I was looking at every possible solution except the mags.

My advise, take your Mooney to a service station. Additionally, have several different pilots fly the plane with you and see if they experience the same issue. This works best if you simply observe rather than demonstrate the problem and let them offer suggestions of what is wrong.

I'm not suggesting you have a mag problem, rather you and your mechanics might be focusing on the wrong location to diagnose the problem. Hope you get your bird back to 100%.

Dan

[FlyDave]

Well, as a number of people have suggested, this was a mag problem. And as Mooney17N suggested it was exactly what he said - the E-Gap.

I had been talking to too many people and getting too many opinions on what this could be. Also, initially I went to a mechanic that I should have walked away from when he initially said "this is a tough one and I'm not sure if I can find the problem" - lesson learned on my part! Then I went to the respectable FBO on field and they went through the fuel system, then moved to the mags. They checked everything and were very thorough (and knew they would find it!).

So I'm back in the air as of 2 weeks ago. Look at my next post about my seat problem for more of the drama!

[JTMech70]

Mags are definite possibility. Slick recently released a Service Bulletin concerning a bad batch of points and mags. I personally ran into this a month ago on a Mooney TLS I rebuilt the mags on and ended up having issues with the points in less than 100 hours. One mag quit all together and the other barely ran. Look at Champion / Slick Service Bulletin 1-12. I believe there is even a warranty for the parts if you still have the box with the lot number on it, if it applies.