[McFly]

Very intermittently when I do a mag check and I turn off the mag (meaning the Light Speed EI is the only spark), the engine dies. I flip the mag back on before the prop stops. When I repeat the test, the EI sparks fine and the engine runs smooth. I have never felt the EI drop off-line in the air nor have I noticed funky temps in flight that would indicate the EI droped off-line but I can't say it has never happened.

I visually inspected the electrical connections and they seem to be solid. Any guesses as to what is happening or how to trouble shoot?

 

[Snowflake]

A local pilot had an intermittent EI problem similar to that, although it only showed up *in flight* and only very intermittently. It was eventually traced back to a poor connection somewhere in a DB-9 (or maybe DB-15?) connector on the back of the EI unit. We found it by running the engine on just the EI with the cowling off, and someone reaching in and wiggling wires until we were able to make the engine miss. I forget whether it was in the cable's connector or in the connector on the EI unit though.

Note that this is an extremely dangerous thing to do, with someone standing and working that close to the prop. Set boundaries (no body parts ahead of the carburetor, etc.) and stick to them. If you need to change the plan, shut down and re-brief before continuing.

 

[rvmills]

Hugh,

Couple questions on the system. Plasma I, II or III? Toggle switches or key switch? Hall effect or crank sensor?

Its an odd manifestation, for sure. Seems unlikely that both coils or all wires would fail simo (or enough of them to cause the shutdown). Partial loss would just cause rough running and mismatched EGTs, as you know. Troubleshooting might start with things that could take the entire EI system down:

- Something in the brainbox itself (short in boards, etc)
- Something in the connection between the brain box and the coils (would have to impact both at once, or the engine probably would not die)
- Something that interrupts or drastically alters the timing signal (enough to cause the shutdown)
- If toggles, could there be a mechanical interference that causes the EI switch to short or shut off when you turn off the mag switch (but doesn't do it every time)?
- If a key, could something have shorted in that wiring? I have toggles, but have read that the EI wiring via a key switch must be done carefully. Its worked for a long time for you, so that's why I mentioned a recent short there, if you have a key sw.

I previously had a LSE Plasma I that had intermittent partial failures (rough running on LSE only). The brain box's first trip to LSE resulted in "could not duplicate". I had already replaced about every component in the system except for the brain box and the crank sensor. The problem hid for a while, then returned in a less intermittent fashion. It would resolve with a warmer engine, but was worse and more persistent than before, so it went back for look 2. This time LSE could duplicate the problem briefly, but it disappeared as the box warmed, or if the box was pressed on the side. The smoking gun in the box was never found, so the old PI was scrapped.

Just relating that story to say if the box is suspect, it could be a small, hard to ID failure within the box, so get it checked before you go to the time and expense of replacing everything else first; and to give you a couple ideas of where to look.

Good luck, and interested know what you find.

And sorry I missed the Bud Man's wedding flyover the other day...dern Reno winds!

Cheers,
Bob

 

[Mike S]

You state it only seems to occur when you do a runup test, and not in flight.

This would lead me to start looking at the switch.

 

[McFly]

system info

Thanks Guys.

Here is my system info:
Plasma II
Toggle switches (wired per Knuckes where you can't crank the starter over with the EI hot)
Crank sensor

Mike: I'll check it out again.
SnowFlake: It may come down to doing jiggling stuff with the engine going, I hope not but well see.

Bob: Thanks for the input. You were definetly missed at Bud Man's wedding. Hope to catch up with you soon.

 

[N427EF]

More info please

Some more info is needed to be able to help and pinpoint the problem.
Does the engine quit as though there was no ignition at all or is there still ignition on one or two cylinders.
Starting on the EI is one of the best benefits of the Plasma EI, and wired as per LSE instructions, says nothing about disabling the starter with the EI on, but that is besides the point.
Before I can tell you more based on my intermittent EI ignition problem and solution a few years ago I have to know more details.
Don't hesitate to give Klaus a call and then follow his instructions before spending umpteen hours collecting bits and pieces of advise.

 

[McFly]

" I have to know more details"

Maybe you have to ask the question as to what details you need. I have listed the symptoms (the engine dies?no ignition) , what I have checked thus far, the hardware that is being used in my system and how it is wired.

Let me know what you need and I will be happy to provide it. Thanks.

 

[N427EF]

Just needed you to confirm that the engine actually dies when the EI is turned off.
This scenario eliminates quite a number of possibilities most of which are more common than what you might be dealing with.
One more thing, how many hours have you flown with this set up?
The symptoms you describe narrow it down to one or 2 things.
RVmills has summed it up pretty well but I would consider a fault in your power supply to the plasma box highly probable.
Although problems with the brain box are rare, they have occured to a few people.
I would start with the toggle switch that supplies power to the plasma by connecting a volt meter and monitor voltage from start up to when you turn the mag off.
I am assuming that the toggle outputs go directly to the plasma brain box??
You should be able to do this with minimal fuss and keep the meter in your lap for a run up check.
Arcing spade connectors at the coils are one of the more common intermittent problems but not likely that both go out at the same time. Looking at these will not tell you anything so you have to pull them off and check for burn marks.
This is probably the most common intermittent problem with the LSI but not likely your problem.