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Inflight Mag Check Anomaly


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I have a M20F with an A3B6 engine. The left mag is a conventional Slick mag and the right mag is an electroair electronic ignition system. Flying at 4500 msl with 21 inches of manifold pressure at about 30 degrees lean of peak, if I turn off the electroair system and run only on the left mag, the egt's for all cylinders stabilize fairly even at over 1400 and the engine runs fairly well.  If I switch to the electroair mag and turn off the left Slick mag, cylinders 1,2 and 4 stabilize at an egt  over 1400 but cylinder 3 drops off and egt goes down to under 400. Engine runs rough.  If I enrich the mixture about 1 to 2 turns, number 3 will come alive and the egt will stabilize at  over 1400 which is consistent with the other cylinders.  Engine then runs smooth.  When I start the process, fuel flow is about 6.7 gph.  The fuel flow at which the number 3 comes back alive is about 7.5 gph.  The plane has gami injectors and the fuel flow is fairly well balanced. I have a JPI 830 engine monitor and am in normalize mode. Checked the resistance in all spark plugs and they all were within specs with readings between 650 and 725. I just installed new spark plug wires for the electroair side of the ignition system and the resistance for all plug wires is within the manufactures specifications. I tried a different spark plug in number 3 and results were the same. Number 3 is my leanest running cylinder.  The electroair plugs are in the lower plug hole.  Recent compression test on this cylinder was 78 over 80.  We looked for an intake leak in number 3 cylinder and were not able to locate any leaks.  This problem does not show up during a runup mag check while on the ground.  Engine has about 900 hours on it and runs great.

My mechanic is not sure why this is happening but does not seem to think it is a problem.  I talked to the electroair tech and he thought it may be caused by the fact that the cylinder is running very lean and there is not enough fuel in the cylinder to be ignited consistently by the lower plug. Once mixture becomes a bit richer, lower plug can ignite it. Upper plug is located closer to the injector where fuel mixture may be slightly richer which enables it to be more readily ignited by the upper plug.  He also indicated it may be related to the duration of the spark being different for the electroair system and the fact that turbulence in the cylinder may kind of blow out the spark. Not sure I agree with the blowing out the spark theory.

My feeling is this cylinder is running so lean that it is just able to fire on the upper plug but not the lower.  I also wonder if the the electroair coil for number 3 is weak which results in a weaker spark that is unable to ignite a very lean mixture.  New coil pack is $510 and I do not want to jump into buying one.  Planing on flying it for awhile and watching it. 

 Any thoughts on this would be appreciated.

Thanks, Jeff

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There is one coil pack for the entire electroair system.  My understanding of the how the coil system works is that there are actually only two coils that are contained in a single coil pack unit.  One coil is for plugs 1 and 2 and the other coil is for 3 and 4.  The way it works is the spark plugs for 1 and 2 always ignite at the same time.  When number 1 ignites during the compression stroke, number 2 ignites at the same time during the exhaust stroke.  Because number 2 ignites during the exhaust stroke, it essentially is a wasted spark. When 2 ignites during its compression stroke, 1 also ignites but it is now in its exhaust stroke.  Process is the same for cylinders 3 and 4.  This is how the system runs 4 cylinders with two coils.  Logic would indicate that if the coil for number 3 is weak, it would also be weak in 4 because this coil is used by both cylinders. This is why tech did not think it was coil issue because we do not see problem in 4. I suppose I could  put the number 4 coil lead on 3 and the number 3 lead on 4 and see what happens.  A little nervous doing this.

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Since the focus up to this point is all around the ignition system...

Allow me to throw in what I suspect...

1) the problem is happening on one of the cylinders under various conditions.

2) the problem goes away when the mixture is enriched.

3) Sounds to me that on eof the fuel injectors isn't delivering fuel properly, as if it has a partial blockage.

4) There is a test for this.  Baby food jar test.

5) There is a cleaning procedure for this as well.  Try to catch whatever comes out for inspection.

6) how would an ignition challenge improve by increasing the mixture?

7) #3 is your leanest running cylinder, normally.

8) #3 is your cylinder that goes off line.

9) #3 is the cylinder that comes back on line when the mixture is increased.

10) still Sounds to me like the fuel injector to #3 is worthy of a good cleaning.

welcome on your first post, Jeff.

These are PP ideas.  Not a mechanic.  Just thinking out loud...

Best regards,

-a-

Edited by carusoam
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# 3 is the hottest cylinder.

Good information could probably be obtained by switching the electroair plug to the upper plug hole on number 3 and put the left Slick plug in the lower hole and see what happens.  I may see if I can borrow some longer plug wires from my mechanic and do this.

With respect to swapping the coils, everything is in one coil pack that is electronically controlled.  While I can probably switch the 3 and 4 leads, I do not think I can switch 1 and 2 for 3 and 4.  I possibly may be able to get a loaner coil pack from electroair to trouble shoot this.

The reason why we have been isolating the problem to the ignition is because #3 runs well on the left mag.  I think I need to take a closer look at the injector and give it a good cleaning. Baby food jar test would give a good indication of what the #3 injector is doing in relation to the other injectors.  

Thanks for all of the good ideas!

Jeff

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#3 is the hottest cylinder and it probably peaks first when when leaning too?

Look where the plugs and the fuel injector are in the cylinder head.

if the conical spray pattern of the injector has been compromised, there is going to be weird /less than optimized distribution of fuel to that cylinder.

When you do the gami test what happens?  How soon does Cyl#3 peak before the others? 0.1 gph, 0.5 gph, or something like 1.0 gph...

Fuel injector blockage happens kind of often around here.  There are some rubber hoses in the fuel systems of the IO360 that have a liner that sometimes sluffs off a few bits that show up in an injector.

Keep looking at everything until you find what is doing it.

At this point, many MSers load a graph of their flight downloaded from their JPI or whatever eningine monitor they have...

It is  amazing what some people see in some of these graphs.  Subtle nuances that are pretty obvious once they are pointed out by somebody in the know...

MS is a pretty powerful place.

Best regards,

-a-

Edited by carusoam
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I have not done a gami test in awhile, but I do remember #3 peaks first and the next cylinder peaks almost immediately thereafter.  I will recheck the gami spread the next time I fly the plan.  I think I will also clean the #3 injector and see if I can switch the electroair plug to the upper hole and see what happens. I think my plug wires are good due to the fact that they are new and the resistance is within the manufactures spec.  Thanks for the input and I will post any additional information I come up with.

Jeff

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GAMI injectors are sized. "IF" you have a larger one on another cylinder, try swapping the injectors. 

IF number 3 peaks first, simply get a larger GAMI injector for that cylinder. It's too lean, too quickly. Mine peak almost identically. Very nice, as I can lean it out like crazy and it remains smooth right up until it quits. 

Be very careful cleaning GAMI injectors. They do not have steel internals and just about any physical object placed inside can damage them. 

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I would run a GAMI spread test to see if all the cylinders are still peaking at the same time. It must have been very good when you first got the GAMI injectors but maybe something happened. Before you take a wrench to it get the maximum diagnostic power out of your engine monitor. Oh I just noticed you plan to do this. Good luck.

David

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