Diagnostician needed!

[Sandy]

My mechanic spent all day yesterday trying to find the problem:

While landing the other night I noticed a slight engine roughness as I retarded the throttle below about 1400rpm. I ran it up after landing and found a slight roughness around the 1200 - 1300 area on the right side (io360a3b6d) of the mag. Next morning my mechanic pulled and machine checked the plugs and found them to be OK. Yesterday we really dug into it; he high voltage tested the wiring harness and found a couple of less than perfect but normal for their age leads, he checked the mag timing and eventually removed it for a deeper inspection. Other than a bit more carbon than normal for the time since last removal everything checked OK. Reinstalled, ran it up with no change - still runs rough at low rpm. At one point it seemed like #4 cylinder was running a bit hotter than the rest but the readings on the JPI fluctuate a bit in those conditions so we can't be sure. And now it doesn't seem to be only on the "right mag".

Have any of you fine folks had a similar experience? It's already cost me eight hours labor with no result, I hate to just start throwing new parts at it.

 

[jetdriven]

Try switching the plugs around. Or trying some known good spares.   Try richening or leaning the mixture and its effect on the roughness.

[Piloto]

The problem could be related to leaks on the intake pipes or idle setting of the fuel servo. Have you tried leaning at 1400 rpm to see if the roughness goes away?. Check the fuel servo linkage for looseness.

José

 

[KSMooniac]

How does it run at idle?  IE will it idle smoothly at 700 or so?  What temps on the JPI were running hotter?  EGT or CHT?  Higher EGT likely indicates one plug is deficient.  Doubt you'll be able to detect CHT differences.  Did you examine the leads for cracks that could be shorting out when installed?  It could be possible to pass a bench check off the plane, but fail on the plane.

[John Pleisse]

I second Jose's notion of MF or possibly sticking valves. Is it a consistant roughness or and ocassional jolt and pop?

[Sandy]

Thanks to all you fine folks who have responded to my problem.

If you'll permit I'll respond to all at once. First, I didn't try leaning and I don't know if my mechanic did. Second, I don't know whether he checked the servo linkage or not. Third, The temps across the board were normal except for that one few second excursion to hotter on #4. Fourth, I don't remember checking its roughness at full idle - I rarely run it there. And, finally I don't know if my mechanic (I'll call him Joe for briefness) did.

What he did do after I left last night to keep from becoming too much of an irritant was, he soaked the injectors overnight then ultra sonic blasted them this am. He saw no visible problem there. Later today he was poking around with his bore scope but I didn't get a chance to talk with him yet.

Others have also mentioned carbon on the exhaust valves as a possibility. Also, a neighbor with a 540 which is similar to a 360 said that he had a problem with carbon on the lifters. I hadn't heard of that before.

I'll gently ask "Joe" about the above unresolved items - you know how mechanics hate others second guessing them.

I'll keep you posted.

Sandy

[carusoam]

Sandy,

 

A good boroscope can tell alot about valves.

 

Stuck valves are scary on take- off.

 

Monitor egts for anomalies.  Stuck valves often send burning fuel down the exhaust...

 

Is this engine new to you?  Has it been sitting a while?

 

Keep in mind, you are not second guessing your mechanic.  You are showing genuine interest.

 

Good luck.

 

Best regards,

 

-a-

[KSMooniac]

Quote: Sandy

Third, The temps across the board were normal except for that one few second excursion to hotter on #4. Fourth, I don't remember checking its roughness at full idle - I rarely run it there. And, finally I don't know if my mechanic (I'll call him Joe for briefness) did.

 

[johnggreen]

Sandy,

Scott's reference to the plug being bad even though it checked ok should have been highlighted.  That often overlooked problem is more common than one would think.  Nice thing is that it is relatively cheap to check.  Buy a couple of new plugs.  Sooner or later you will need them anyway.  It could be a sequence of weaknesses in the ignition system that are simply getting enough mass at that one cylinder to be causing a problem.  I have one of my mags replaced every second annual and will throw away plugs at just the hint of a problem.

My money on this problem goes like this; 50% valve issue, 30% plug, wire, or connection, 20%, fuel injector.  I will be very curious to know what does resolve the issue.

JG

[jetdriven]

Com to think of it, Testwest checked the ohms of the Champion plugs in his Aerostar and most were really high resistance.  Somwe sort of breakdown of the resistor in Champion massive plugs. 

 

http://www.mooneyspace.com/index.cfm?mainaction=posts&forumid=3&threadid=2470

[Sandy]

Progress to report - none.

To respond to your questions:

carusoam - No, the engine is not new to me and it is flown weekly.

johngreen - The temps I was referring to were the EGT and CHT on the JPI.

Thank all for your interest, I probably won't have any news until Monday. I will let you know what the problem is.

Sandy

[Sandy]

Sorry it took so long to update my problem. I couldn't make the site work yesterday. "Joe" tried everything he and we could think of and the problem with my aircraft still exixts. He hopes to obtain a like new complete ignition harness so we can swap it with mine and see if there is any difference. I've flown the bird twice since we gave up trying to fix it and it runs fine - except for that occasional "stumble" at low rpm. I'll update if and when.

Sandy

[Shadrach]

More info would be nice. Does the engine surge at idle (seem to cut out for a split second) when hot?  Is it an actual stumble (a miss) the causes vibration.  

If you have an actual stumble, I'm betting on intake leak.  

[jetdriven]

check the sniffle valve and the other stuff Don talks about in this link.    Also check the muffler for broken or blocked flame tubes inside.

 

http://www.donmaxwell.com/publications/MAPA_TEXT/External_Hoses/External_Hoses_Tubes.htm

[moodychief]

My engine was not running as smooth as it should.  We had evidence of an intake leak (replaced all gaskets and hoses), but as we were checking everything else we discovered the manifold pressure tubing actually had a hole you where it passed through a bracket (that caused the hole) on the side of the engine. The manifold pressure on mine connects to the right front cylinder.  It makes me wonder if that didn't contribute to me having to replace that cylinder ten hours earlier due to that cylinder sucking air and running leaner than the rest.  I only have a single CHT gauge on my left rear cylinder.

I'm not a mechanic so forgive me for talking in laymen's terms.

[kerry]

My O-360 runs rough at 1200-1300 range.  I found a induction leak which was repaired and it still didn't correct the roughness.  After speaking to many mechanics I've been told O-320 and O-360's are known for running rough in this range and was told simple don't continuosly run your engine at this range

[Shadrach]

Quote: moodychief

My engine was not running as smooth as it should.  We had evidence of an intake leak (replaced all gaskets and hoses), but as we were checking everything else we discovered the manifold pressure tubing actually had a hole you where it passed through a bracket (that caused the hole) on the side of the engine. The manifold pressure on mine connects to the right front cylinder.  It makes me wonder if that didn't contribute to me having to replace that cylinder ten hours earlier due to that cylinder sucking air and running leaner than the rest.  I only have a single CHT gauge on my left rear cylinder.

I'm not a mechanic so forgive me for talking in laymen's terms.

[moodychief]

Quote: Shadrach

That's odd, most 4 cyl Mooneys that I've seen use number 3 (Rear right and typically the hottest) for both the MP pick up and the single CHT and EGT.

[Sandy]

I suppose I should put an end to this issue. I've flown it four times since we quit trying to diagnose a problem and all appears normal. Should anything interesting occur I'll report. Thanks to all who offered support.       Sandy.

 

[mooney2201]

check the sniffel valve on the botton of the engine....if the valve hangs up it will run lousy,,,,,poor idle ect.....

[Sandy]

That was one of the many things we did 2201, the ball was free but "Joe" squirted something into the tube just to be sure. It's still running fine!

Sandy