Ign causing failsafe

[Wind Junkie]

I'd like some help if this sounds familiar to anyone.

I've been flying my TBM P40 with a DA 85 for a few months now. About 3 weeks ago, I had what I thought was an engine problem when the motor would cut out at some speeds-- usually downlines. It was consistient. Then the problem got worse and I noticed that it was not the motor's fault because I would watch the throttle servo go to idle when I'm just running up in the pits-- an obvious failsafe condition.

Range checks WITHOUT motor running are good. Today I switched to a new RX and even switched to a different TX, and all have the problem. I changed to a new throttle servo also. Range check with motor running is VERY BAD-- it goes to idle immediately and I can see the failsafe trying to activate at most throttle speeds when I'm standing right over the airplane (it pulses for a half second or so and makes the motor sound like it's hesitating, but really it's just the throttle commanding it). This will happen with me simply holding the RX in my hand (either RX) with only the throttle hooked up, and with either of two TX's I am using for test.

The only thing I can think of is perhaps I may have put some stress on the spark plug wire in fishing it through the hole in the cowl in the past month. Someone told me that if there was arcing inside with a "carbon wire" in that area it could give interference.

My question is I thought 2.4 would filter out such noise? I have seen threads where 2.4 users share a SINGLE battery for both RX and IGN, but I guess what I'm asking is it possible that the high voltage side of the circuit is more likely to cause proglems if it arcs?

If one can share a battery with IGN and RX, it seems obvious that position of the components near each other (which I understand was a big no-no with 72MHz gear) with 2.4 equipment wouldn't seem to matter. I do have the RX batter near the carb, and the ign module is also near the carb, about 5" away. The throttle and Ign switches are separated by only 3" and that's the closest their wires get to each other.

The thing that bugs me is I had beautiful performance since mid July and after Labor Day something changed drastically, so it seems to point to something other than equipment layout.

Does anyone have experience in this area?

thanks,
Joe

[classclown]

Joe, was it not you who had the muffler problem on that plane a while back? If so, inspect the muffler. If it is slightly loose, it will cause your RX to go into failsafe. Found that out with one of my helis. But the failsafe put it into throttle hold, and I had about 3 to 4 degrees of neg pitch set for failsafe, so the heli auto'd itself into a corn field. Not one single scratch, nothing bent. Found one of the bolts on my muffler slightly loose, tightened it up, everything is fine. Also, check your spark plug cap and the braided wire for it. I thought it only did that on 72 myself.

[wylieruneyjr]

Wish I could offer some help. I experiaced a lost signal "drop out" but my set failsafe positions never went to there set positions.?????? CRASHED Suggest you ground that warbird til you figure it out.

[Wind Junkie]

Yea, this is the 3rd muffler for the plane, but I think I got that issue all ironed out. It has 3 flights on it and no issues yet-- (still tight).

The motor will probably go back do DA soon to get that piston upgrade people are talking about to smooth it out. I think she is grounded for the season, but if someone had an idea about how to fix/test this radio issue I'd love to try it beforehand.

If I do send the motor back I will also send the ign so maybe DA can check that out too.

[classclown]

Did you check to see if the plug cap is ok? pushed all the way in? What about the shield for the wire? It might have rubbed on the fibreglass cowl and ripped open in a certain spot. Howz the TX with your other models?

[castlebravo]

Ignition noise will interfere with 2.4ghz systems! It may not interfere with the signal to the radio but it will certainly get into the actual servo leads and cause the servos to do some very odd things. I have had it happen on two seperate airplanes with 2 different engines. My first was with a Fuji-43 that was so noisy it would cause the flaps and aileron servos on a Giant Ugly stick to go crazy. I had to seperate the ignition system and the radio by several feet to get it stabilized.
My latest incident was caused by a DA-50 with a bad ignition. Caused my throttle servo to lock into high and before I could do anything....it pulled the whole start stand with my airplane in it (one of those big AMA wood starting table/stands). The stand crunched my Edge really nicely. I found out when I put the motor in another airplane that it was the ignition proximity to my throttle servo that was the issue. That motor is going back to DA because it certainly shouldnt happen. Both of these aircraft are on 2.4 ghz FASST.
2.4ghz is not the end all when it comes to interference.....we still have to deal with the laws of physics and and a strong RF signal can be induced in any electrical system no matter how "Immune" it is supposed to be.

CB

[Wind Junkie]

Hmm. Well, I definitely believe you guys about 2.4 not being the cure all for interference (anything can be jammed), but in my case it's not the noise causing the servos to jitter, cause it goes into failsafe (no jittering, last known position on all flight controls, and only throttle moves-- to idle).

The spark plug cap is on all the way, but I did need to repair the red shrink tube which bridges where the braided shield enters the metal cap. When the plug floods I always need to pull the cap off with needle nose pliers through a small hole due to the cowl hiding everything. Sometimes I pull too hard and the cap gets jammed in the hole-- maybe kinking the wire.

I just thought of something else. I have both the sensor wire and the spark cable going through the same hole in the fiberglass fuselage from the ign to the motor. Both are wrapped separately in plastic coil protector, but maybe that has found a way to work loose and fray? I wonder if there would be a path for noise to enter into the RX back through the sensor wire.

[N726AC]

Try changing the spark plug, I saw something very similar last week.

[bodywerks]

Also, if you need pliers to get the spark plug cap off you're doing something wrong or there is something wrong with the cap itself. All you should have to do is align the two openings(where the two halves of the cap come together at the spring ring) of the cap with two of the points of the 'nut' of the spark plug and pull straight out. I've never had to use pliers of any sort.

[bubbagates]

Joe,

Even 2.4 can get swamped if the signal is strong enough. Since you have been pulling on the plug cap improperly with pliers and most likely from the side and also had to repair the cap at the joint in the wire, that would be my first bet. Vibrations, especially from a big single cylinder engine will eventually show you the weak points on any plane.

To give you an idea, I installed a DA170 into my 42% Extra, 45 flights later I was taking hits and the engine was roughing rough. I got the plane down and found both plugs a bit loose. I tightened them and have not had a problem since. I t was my own fault for not checking them when installing the engine.

Yes, carbon wires can be a bit of an issue, especially when treated roughly. Also, if any of the protective braiding around the wire is damaged, which is also the ground for the plug/ignition connection, you will also get interference even on a 2.4 if the damage is severe enough

If you are flooding enough to have to do pull the plug every so often, then you are way too rich as well on the low end. Remember, you never ever have to run a gas engine rich, you do need to properly tune it and if cooling is an issue and you are running it rich to get it to run cooler, I'd be looking at airflow as well as oil mixture. Oil mix and airflow are what keeps a gas engine cool. Running one rich robs it of power and fouls the plug and causes flooding.

The low end needle on a DA85 is very sensitive, so start out with no more than a 1/16th of a turn at a time until it can idle for a long time without the idle speed changing. Then do the high speed needle to get max rpm and drop it back around 100 rpm. You are looking to get instantaneous response to the throttle. Fly it and go vertical for all it's worth and listen to make sure the engine is not sagging on the upline, if it is, then it's too lean. Do all the adjustments with the cowl on.

[Wind Junkie]

Thanks for the tips guys. To clarify, the only reason I need pliers to get the cap off is because the hole in the cowl is very small and I can reach the cap by just gripping the "flange" which is an artifact of how the plug cap is made. I doubt very much that it hurts the cap itself. I just put the tips of needle nose pliers through the hole, grip the flange, and pull (no harder than you would just using fingers, and the pull goes straight down.

A couple times I pulled too quickly and part of the cap came through the small hole in the cowl and got jammed-- also putting stress on the rear part of the cap/shield so that is where I think the damage may be.

Also, the carb floods only at the start of the flying session. This is because if I don't drain the tank, it has a habit of flooding when I store the plane nose down. Both my DA 85's do this (stored nose down due to space) so I'm assuming that's normal. Neither floods anymore after the first start.

Now I'm getting into the habit of draining the tank-- mostly cause it will leak a little over time anyway and I don't like gas fumes in my basement. But it never floods anymore when I do that.

But it is good to know that the spark plug end can cause 2.4 issues. Thanks again for your replies.

Joe

[classclown]

	Quote: Originally Posted by Wind Junkie
	Thanks for the tips guys. To clarify, the only reason I need pliers to get the cap off is because the hole in the cowl is very small and I can reach the cap by just gripping the "flange" which is an artifact of how the plug cap is made. I doubt very much that it hurts the cap itself. I just put the tips of needle nose pliers through the hole, grip the flange, and pull (no harder than you would just using fingers, and the pull goes straight down. A couple times I pulled too quickly and part of the cap came through the small hole in the cowl and got jammed-- also putting stress on the rear part of the cap/shield so that is where I think the damage may be. Also, the carb floods only at the start of the flying session. This is because if I don't drain the tank, it has a habit of flooding when I store the plane nose down. Both my DA 85's do this (stored nose down due to space) so I'm assuming that's normal. Neither floods anymore after the first start. Now I'm getting into the habit of draining the tank-- mostly cause it will leak a little over time anyway and I don't like gas fumes in my basement. But it never floods anymore when I do that. But it is good to know that the spark plug end can cause 2.4 issues. Thanks again for your replies. Joe

Only thing is, now that you drain the tanks, you fuel lines will harden up.

[ScottZ]

I had a similar problem with a plane a few years ago. After long tests on the ground changing almost everything out, it turns out that it was the resistor in the spark plug cap since the CM 6's aren't resistor type plugs like in cars. You can't fly a plane if this resistor is damaged or arcing. Radio Shack has these resistors or you can get them from the company who sells the motors. The pliers was what caught my attention on this post.