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  #1  
Old 12-16-2011, 08:34 PM
Speeddog7 Speeddog7 is offline
 
Join Date: Apr 2010
Location: Plano, Texas
Posts: 42
Default Engine Concern (perceived mis)

Any of you guys have a suggestion on the issue I'm having?

Superior IO-360 with high compression pistons (185hp), Hartzell Blended Airfoil, Silver Hawk fuel servo(Bendix) with ram air (no filter at the moment), Slick mag on the left, Lightspeed ignition on the right. The engine has about 130 hrs on it now. The engine starts easily and generally runs fantastic on the ground and feels/sounds strong during takeoff and climb. That being said, when I power back to say 21" and 2450 RPM, the engine generally sounds good, but I detect an intermittent "miss" or hesitation. Its just enough to make me not fully trust the engine 100% and it wears on my mind. The Dynon D180 shows the engine as being perfectly healthy. All the CHT's and EGTs look great and within a few degrees of one another. Oil temp stays in the 180 degree range. When I do my engine runup, I get a big decrease in RPM if I turn off the Electronic (probably 200 or 300 rpm), so the mag seems weak. When I turn off the mag of course, there's very little drop. In flight, if I turn off the EI, the engine of course runs poorly, so it's hard to tell, but I think I still feel the intermittent miss. If I turn off the Mag, I still think I feel the miss. I've checked timing on both the Mag and EI. I've verified that the coax wires coming from the electronic ignition aren't in close proximity to the crank sensor wires. I've monitored fuel pressures. The boost pump doesn't make any difference in the "miss". To me, it seem to be related to ignition. I've pulled the prop and verified the correct location of the sensor magnets, the spacing between the sensors and flywheel magnets and I've confirmed correct orientation / timing of the flywheel to the crank sensor.

With the above in mind, whats the likelihood of having an intermittent stuck valve that's causing my problem? Do valves intermittently stick? Does a sticky valve ALWAYS show up on electronic engine monitors? I'm not seeing any power loss or anything reflected in EGT or CHT's on the Dynon. Its rock solid as far as temps. The only thing I've noticed that seems to make the "mis" either go away or become less detectible is to run higher RPM's and MP's. During takeoff, at full power and high RPM, I've never noticed the mis and it runs strong. It only seems to be a constant issue at more reasonable cruise power settings where I always want to run to conserve fuel. Mixture setting doesn't seem to affect the mis whatsoever.

Any help would be appreciated as I'm running out of ideas. I'm considering going dual electronic ignition or installing a bendix mag which I've been told produces a stronger spark than today's slick mags, but I'm just not sure the mag is my problem (even though I feel it's weak considering the amount of mag drop I'm getting). My friend has the same exact engine/mag/electronic ignition setup in his 7A (but with standard compression) and his engine runs GREAT!

Any Ideas?

Chad
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  #2  
Old 12-16-2011, 09:02 PM
molson309 molson309 is offline
 
Join Date: Jul 2009
Location: Longmont, CO
Posts: 254
Default

Is the flywheel magnet-to-sensor gap maybe becoming too large when you pull on the prop? There is some play there and the gap will definitely change when the prop is pulling the airplane.
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  #3  
Old 12-16-2011, 09:11 PM
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DakotaHawk DakotaHawk is offline
 
Join Date: Oct 2008
Location: Arlington, WA
Posts: 801
Default

Chad,

The best way to troubleshoot this "phantom miss" is to make a flight on a moonless cloudy night over a large body of water. Studies have shown that the average pilot's sense of hearing is vastly improved under these conditions.

Sorry - wish I could help with some tidbits of knowledge that were actually useful!

But really - I have the same setup (Lightspeed and Mag). I have the same RPM drop on run-up of about 250 RPM. I don't consider it to be a problem, because the LS Ign is so strong, the Magneto just doesn't have the output to match it.

You asked about the possibility of a stuck valve. You would see a stuck valve on your EGT. Pretty tough to get an "intermittent" stuck valve, so that's probably not the problem.

You might want to aggressively drain both sumps for water, as well as clean the fuel filter. Also, make sure your injectors are clean.

Finally, download your EMS data and scrutinize it. If everything is, as you said, "perfectly healthy", then you're probably OK.

Good luck!
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  #4  
Old 12-16-2011, 09:23 PM
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rocketbob rocketbob is offline
 
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Default

First thing I would do is eliminate the easiest thing and that would be to change the spark plugs.
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  #5  
Old 12-16-2011, 09:36 PM
DaAV8R DaAV8R is offline
 
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Location: Lee's Summit, MO
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Default Miss

I don't know the first thing about electronic ignition but I've had these exact symtoms in the past. I had an intermittent miss that I couldn't figure out for about 25 or more hours. I finally saw the egt blip and changed the plugs in the offending cylinder. Problem solved. I also think there is a strong chance you have a plug problem.

The plug that caused me all the problems was a nearly new Champion.
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  #6  
Old 12-16-2011, 10:46 PM
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lostpilot28 lostpilot28 is offline
 
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Location: Boise, ID
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Quote:
Originally Posted by rocketbob View Post
First thing I would do is eliminate the easiest thing and that would be to change the spark plugs.
Bob has a great point...I had a very, very slight miss a year and a half ago while flying to Reno. I've got dual electronic ignition (PMags) and it normally runs smooth as silk, so when it missed it caught my attention. Upon returning home, I pulled the plugs and found that they all had tiny lead balls stuck to them. Changed them out (auto plugs at $2.50 each) and it went back to running perfectly. Since then I've mostly been running auto gas. Problem has not returned.
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  #7  
Old 12-17-2011, 06:50 AM
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RV7Guy RV7Guy is offline
 
Join Date: Jan 2005
Location: Chandler, AZ
Posts: 3,062
Default Another simple check

Others have mentioned the plugs and that is a good and simple idea.

I had a similar problem. Cleaned the plugs and it would still happen during a certain RPM range. I would think if it was ignition, it would be pretty much across the board.

Discussed it with one of our local A&P's. He suggested that I check the Fuel Injection system. He showed my how to pull the lines from the cylinders and place a cup under each one. The fuel pump was turned on, throttle full. We ran this for about 20 seconds or so to get about half a cup.

Well the Number 1 cylinder only had about half as much fuel in the cup indicating some sort of blockage. I pulled that line from the spider and flushed it. I found a small speck of black rubber material in the line. I also checked the spider and found it clean.

Everything was put back together and the engine performed flawlessly. The mechanic explained that the piece of rubber could be floating and cavitating in the line causing intermittent fuel flow. That lead to the inconsistency.

Good luck.
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  #8  
Old 12-17-2011, 07:14 AM
Pat Stewart Pat Stewart is offline
 
Join Date: Jan 2005
Location: Granbury Texas
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Default Spark

Quote:
Originally Posted by rocketbob View Post
First thing I would do is eliminate the easiest thing and that would be to change the spark plugs.
I agree with Bob, I would start with spark plugs, put them in a tester at 80 PSI and check the spark.

Pat
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  #9  
Old 12-17-2011, 07:32 AM
Tom Martin Tom Martin is offline
 
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Location: Ontario, Canada
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Default

Start with the plugs as suggested
Valves: note egt's at the start in the morning and see if there is any difference, this is commonly called "morning sickness", but it they are just sticking a bit the engine still might idle ok but you may see a difference in the EGT. I have noticed a sticking valve in the air after a power reduction, just a subtle blip, and then gone. Nothing showed on the data but the pre take off egt data told the tale.
Mag: This last year I had a miss that I felt was ignition, I changed the plugs, spent a lot of time with the electronic ignition and finally sent the mag in for a check and an overhaul (500+hours). It turned out I had a cracked distributor cap and with that solved all the problems went away. I was a full month chasing that miss.
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  #10  
Old 12-17-2011, 08:15 AM
Speeddog7 Speeddog7 is offline
 
Join Date: Apr 2010
Location: Plano, Texas
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Default

OK Gentlemen. Sounds like plugs first, then move forward with mag inspection. I do appreciate all your input. I'll post what I find. (sure hope I find something....)

Thanks!!!
Chad
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