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  #1  
Old 12-22-2017, 02:54 PM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 698
Default Engine misfire help...

I just finished my third condition inspection. Before the inspection my engine was running great. On the first flight after the inspection I was about 15 minutes into the flight, at full power, climbing through about 4000 ft. when I got what I can only describe as a misfire. I continued to climb to 7000 ft. and got 3 more misfires, on the way up. I then leveled off, pulled back the power and headed back to the airport. I did not get another misfire.

In the first 15 minutes of the flight I was cruising at about 2500 ft. and probably 50% power. I did not experience a misfire during that portion of the flight nor on takeoff.

I have basic Van's instrumentation, so I do not have recorded flight or engine data. I also did not have the presence of mind to do any diagnostics. I was focused on gaining some altitude and getting back to the airport.

Mag checks on the ground were fine.
Startup and idle were normal.

Here's the basics of my engine:

1 P-Mag, 1 slick mag
O320-D3G
TSMOH @1150 hours

Here's what I did during the condition inspection that could potentially be related:

Ignition related
Replaced auto plugs on the p-mag, gapped
Cleaned aviation plugs on the slick mag, gapped
Removed and checked p-mag, retimed.
Retimed slick mag, it was about 1 1/2 degree off (it was overhauled last condition inspection. I think some drift is normal.)
Slightly re-routed plug wires
Ohm check on auto plug wires

Induction related
Replaced intake pipe gaskets. (two were leaking)
Replaced intake pipe hose and hose clamps.
Cleaned air filter
Cleaned gascolator (no debri found)

Oil related
Removed oil cooler, repaired baffle cracks, replaced oil filter
Rerouted bottom oil cooler line to avoid chaffing
Replaced, rerouted breather tube to avoid new oil cooler line placement

I'm not sure where to start looking for the problem. So far I have rechecked p-mag and mag timing. Replaced the new auto plugs with another set. Looked for signs of intake leaks (blue stains, I'm not sure how long it would take so show up) Rerouted plug wires so that the aviation wires do not cross with the auto wires. (they were touching in one spot) My auto plug wires are separated as described in the installation instructions.

Having done this, my inclination is to go for another flight, staying close to the airport and if the problem persists, I will do a mag check at altitude, turn on the boost pump at altitude to see if the problem goes away.

I would appreciate any other diagnostics suggestions to help me find the problem.

Thank you,
Michael-
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  #2  
Old 12-22-2017, 03:07 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,676
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I'd probably fly it. If you have another problem, triple check the timing.
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  #3  
Old 12-22-2017, 03:14 PM
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Larco Larco is offline
 
Join Date: Mar 2005
Location: DVT Phoenix
Posts: 1,254
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Could very well be some little pieces of carbon from cleaning the plugs that came loose and lodged to temporarily foul the plug or two. Have seen it happen and have had it happen. Something to consider?
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  #4  
Old 12-22-2017, 10:12 PM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 698
Default Cleaned plugs again

I removed the 4 aviation plugs today and two of them had what looked like metallic debri from cleaning in the bottom. (I had the plugs cleaned and tested by an aviation plug cleaning service) I dislodged and blew out the debri. Perhaps that was the problem. We'll see.

Still looking for other suggestions on diagnosis.

Thanks,
Michael-
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Last Donation: December 2020

Last edited by Michael Burbidge : 12-22-2017 at 10:16 PM.
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  #5  
Old 12-23-2017, 12:09 AM
tim2542 tim2542 is offline
 
Join Date: Aug 2009
Location: Redding,Ca
Posts: 633
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Altitude related always makes me suspect the plug leads or plugs. Do you per chance have the auto plugs with screw on terminals?
If so swap them out for the solid top variety. Also make sure all the wires are seated properly.
Without an engine monitor it?s a lot harder to diagnose.
Tim Andres
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  #6  
Old 12-23-2017, 07:47 AM
pa38112 pa38112 is offline
 
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Location: Clarksboro, NJ
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Reading the list of things you did - rerouting the plug wires jumps out at me. I would look for chafing, looseness, possible induction issue.
I would also re-time both mags - for example, are you sure you timed the Pmag to TDC, and not 25 before or TDC with the Slick mag. I have heard of people making that mistake.
Curious why you would send your plugs out for cleaning? What can a service do that you can't, and does the guy working there take as much care as you? (Obviously not if you found debris in it!) If he drops your plug is he going to eat the cost of it, or hope nothing happened? If I drop a plug I throw it away and kick myself. A dropped aviation plug could lead to your symptoms.
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  #7  
Old 12-23-2017, 09:06 AM
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can you do a mag check to see if you can isolate the problem to one mag or the other?
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  #8  
Old 12-23-2017, 09:32 AM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 698
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I did have the screw type terminals. The solid terminals are hard to find. I have now found some and the second new set I put in are solid terminals.

I verified timing on p-mag at TDC and on mag 25 degrees.

Reseated all plug connectors.

I send my plugs out because I don't have a plug tester. They are pricey, and this place has always done a good job. But I hear your point and will reconsider in the future.

I'm planning on flying today to see if I've fixed the problem.

Thanks for the help,
Michael-
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  #9  
Old 12-23-2017, 09:33 AM
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jliltd jliltd is offline
 
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Location: Rancho San Lorenzo
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Good ideas in all the responses above. With respect to induction leak misfiring, I think it would be more likely to surface at lower power settings and at idle rather than full power. Like during taxi in from a flight. That's because with the engine at idle or low power the mixture will be extremely lean and out of whack. At full power when the carburetor butterfly is fully open the mixture wouldn't be as overly lean due to the increased fuel ratio in the mixture. A symptom of an induction leak would be no rise in RPM where there was one before as you pull the mixture to idle cut-off. Also, since you corrected some intake leaks during the condition inspection you should go through the process of re-adjusting your idle air mixture screw per the carburetor manual. I would consider this adjustment mandatory due to the work performed.

I haven't heard of a professional spark plug cleaning service before. There must be as many piston airplanes as there are boats in the Puget Sound area to support that business model. I have no doubt the owner of that business is 100% trustworthy. But maybe he had an intern working for him who isn't as cognizant about the reprocussions of a dropped plug.
Be aware that if a dropped spark plug is re-used the cracked porcelain can lead to catastrophic engine failure due to pre-ignition. Not detonation (although that can exacerbate the problem) but pre-ignition. Pre-ignition is the worst of the two. The porcelain insulator inside the plug shields the cylinder chamber from the hot parts of the spark plug so if this porcelain is cracked and compromised the fuel-air mixture can be ignited by the hot plug prior to the magneto-controlled spark. The same pre-ignition trouble could have been caused by the debris you found in two of the plugs.

Also, if your 4 aviation spark plugs are Champion name brand and are over approximately 4 years old then change them. Champion plugs had an issue causing pre-ignition and the company re-designed them and re-vamped their production line since then. Same part numbers. Doesn't apply to the Tempest or other brand(s).

Jim
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Last edited by jliltd : 12-23-2017 at 09:37 AM.
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  #10  
Old 12-23-2017, 11:07 AM
tim2542 tim2542 is offline
 
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Location: Redding,Ca
Posts: 633
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Yeah, I often have order the correct plug, but I?ve fixed the same issue you are having by using the solid top. You can crimp the threads a bit to provide a ?self locking? feature, but I?d suggest you just order up a dozen NGK 3961 plugs from amazon or Napa and have them on the shelf for later.
The 3961 is the p/n for ngk solid top BR8ES plug many of us run.
I have also had to replace a Pmag harness that tested fine as to resistance, but keep giving me a little high altitude misfire.
BTW, you may find the silicon dielectric grease in the plug boot blackened if the plug screw top or connector was loose.
Tim Andres
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