Series of bizarre symptoms

[patterson]

After takeoff I noticed that my EGT on one cylinder was going very lean then it would richen up all by itself. I was working on stabilizing the mixture and soon the engine started missing, even at full rich. I did a mag check and the one Light speed Plasma ll seemed to be the problem. Ran fine on the single mag. As I headed back to the airport to scrub the flight everything returned to normal, except the voltage from the alternator dropped to around 12.7 and never got back above 13.1

Landed without incident but very confused by these apparent electrical issues. I should note that I had another alternator issue some months ago and I replaced it, plus a battery, with new ones. Any ideas what might be the problem?
Thanks
Ron

[Mike S]

Fuel injection, or carb??

[Ralph Inkster]

First thought Alt & Ign symptoms are coincidental but not related.
Ign
1, check plug resistance to see if failing.
2, check spade connectors on ign coil, if one spade black, replace the female side & clean male side with sand paper, coil may have to be replaced if too corroded.
3, check plug wire.
Voltage drop
I'd check all connections on the Master circuit, something might have been jarred while making the lAlt repairs.

[SHIPCHIEF]

Lightspeed ignition runs off from Ship's power.
Your problem with the ship's electrical system might not be the alternator or regulator, it could be the main contactor has gone to high resistance, or some other critical connection is going bad.
Shutting off one Lightspeed unit reduced the electrical load (at least on that branch circuit), allowing the line voltage to the remaining ignition to remain high enough to function properly?
Sounds like you might have a dangerous condition.
For example, if one circuit breaker powers both lightspeed units, and it is going bad.
Or, it's possible the voltage regulator is working fine, but a high resistance exists on the line back to the battery, so reference voltage to the regulator is 14+ but battery voltage is low.
Like Ralph says in the post above, check connections for high resistance or indications of heat damage from high resistance.
Tracking down electrical gremlins can be difficult and time consuming, but if you do it, you will know your electrical system better.

[Mike S]

Originally Posted by SHIPCHIEF

For example, if one circuit breaker powers both lightspeed units,

Sounds like it is a one mag, one LS. system.

Originally Posted by patterson

the one Light speed Plasma ll seemed to be the problem. Ran fine on the single mag.

[patterson]

I have a newly installed fuel injection (AFP150). I thought the rough idle at startup was just the FI. The runup was fine.
R

[SHIPCHIEF]

Sorry I blew it on the Mag/Lightspeed.
You might look into the archives on lightspeed failure modes as well.

[mahlon_r]

Sounds to me as though that cylinder was running on one sparkplug causing the high EGT and then the second plug started to fire and the EGT returned to normal., Bad plug or cable possible in my mind. definitely worth checking....
The voltage change could be the regulator. Some will normally allow voltage to be a little high when cold and then drop the voltage a bit after they get warmed up.
Could you have two separate issues?
Good Luck,
Mahlon

[jjconstant]

May or may not be specific to the symptoms you're seeing, but I had egt symptoms that were variable and baffling and I finally checked the egt sensor itself and it was toast. Very easy to check and fix (order new one!).