M20J Electrical Troubleshooting

[Drew_Wagner]

My 78' M20J has had a couple of odd electrical happenings the past couple of flights and want to see if there are any experts or fellow owners who have had the same issues and found the culprit or if these could potentially be all from a similar issue?

Issues:

- Wobbling Ammeter (going to first try Don Maxwells suggestion of cleaning Master Switch and connections here), but I have noticed that over the last two flights the high/low warning light has come on and instead of a slight wobble it is doing about a 1/4 deflection in the wobble that is pretty big. Unfortunately I just found the article so I need to go fly and see if putting pressure on the contacts stops the issue. In flight intermittently the voltage will go to 14.3V when wobbling and then return to a normal 13.9V-14V reading.

- I replaced the Battery/Master solenoid (with sign off from A&P) because it was original to the airplane and was in bad shape with the SkyTec PMA'd one, but when I turn the master on it always clicks the solenoid, but does not always immediately power everything up. I usually have to cycle it a couple of times to get it to actually provide power. Once it works it works though and has never shut off after engaging. I put a volt meter on it and the battery has around 12.9V on the front of the Solenoid but only 12.3V once the master is turned on on the back side of the solenoid. Is this a normal drop? On my JPI 830, it is around 11.9V in the cabin. I have not removed the JPI to get a reading at the terminal, that is just the reading on the screen. Plane starts fine and seems to have enough power. Is this kind of drop pretty normal under load  and I am being overly paranoid or does that sound like something is amiss?

- I pulled the top and bottom cowl to inspect my alternator and starter wiring and I have concerns about wire integrity and potential corrosion. As you can see from the photos I attached, there is a seemingly pointless splice in the line going to the starter (image 0598) and the alternator wiring has lost a majority of its shielding and is fraying badly. Is it time to replace one or both of these or is this "normal"?

[ArtVandelay]

I think the braided wire is a ground.

You problems sound like a master/avionics switch problem, I would clean both.

I don't like the voltage drop across the solenoid, I would have expected it to be 0.1v or less, it shouldn't have hardly any resistance when closed.

Also I noticed what looks like a caulking fix to the airbox, I'll let more knowledgeable MSers weigh in, but I'm surprised that's legal.

[Guest]

The white silicone on the air box is typical sealant.

The braided cable connected to the fuel injector is meant to ground the alternator to the engine.

The starter cable is spliced with 2 different sized cables. The boot has fallen off.

The  Adel clamps securing the wiring are missing the rubber portions.

Lots of oil everywhere.

looks like the baffle tie wire is rubbing on the oil return line.

Clarence

 

 

 

[Drew_Wagner]

Clarence, had a recent oil change is that normal to have that much oil or is that cause for concern? My last oil report was great with no metal. I cleaned the oil with shop towels before closing. I just like to know what to expect before walking blind into a shop!

Would you recommend replacing all of these wires?

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[Guest]

2 minutes ago, Drew_Wagner said:

Clarence, had a recent oil change is that normal to have that much oil or is that cause for concern? My last oil report was great with no metal. I cleaned the oil with shop towels before closing. I just like to know what to expect before walking blind into a shop!

Would you recommend replacing all of these wires?

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Drew,

Sloppy work during an oil change may account for the oil.  I'd wash the engine down with mineral spirits and compressed air and run it up to see if it's old or new leaks.

The wires used in the engine compartment are an old style with plastic covering which gets hard and brittle with age.  Certainly some repair/ tidy up is in order, that may go as far as replacing wires back to the firewall.  Opening the harness for inspection will be a starting point.

Clarence

[Drew_Wagner]

Thanks for the info. Taking it to a MSC in the morning here in SC. Anybody with feedback on Precision Air?

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[carusoam]

Just for a baseline....

Oil drips are not normal for Mooneys.  Each drop of oil is coming from somewhere.  That somewhere can be identified, tightened or sealed...  I was told drips were exterior lubrication and all engine blocks had this.

there are a lot of seals or oil return hoses that can be easily changed.  And there are some that are a big hassle to change.

A real oddity would be an engine block crack.  Things like this are better to be known, than wait for annual...

And +1 for the voltage drop accross a solenoid.  Something isn't working correctly with that device.  It isn't closing properly.

i'm only a PP, not nearly as knowledgable as the guy with the IO720. 

Best regards,

-a-

[Drew_Wagner]

Just got back from the shop and thankfully the starter issue that I have been chasing for a while showed its head while I was there so we ran through the SkyTec troubleshooting guide and had 11V at the starter when engaged so looks like its time for a new starter. Going to send the old one in for a new solenoid on the starter. After two hours being there it started right up once it cooled down just like before. Should be in on Friday and will take it back to swap them out.

Quick question for any of you Mooney M20J guys, on my battery/master solenoid that was replaced there were two small terminals and two large terminals. One of the small terminals goes to the Master and engages the solenoid, which was put onto the single small terminal. The other one has a fuse in it and was connected to the "hot" side of the solenoid with the other connection. When I disconnected this via the fuse, the voltage drop went from .5 to .1. Any idea what it is? We couldn't figure it out. I searched the electrical schema and it appears to be the analog clock as best I can tell? Could the clock have that type of voltage drop? Either way I left it disconnected and will figure it out another day. Nothing other than the clock appeared to be not functioning.

We did the Don Maxwell fix for cleaning the contacts and they appeared to be clean but sure enough on the way back there was no wobbly ammeter and it showed positive charge for the first time in a while. Its amazing how such a small amount of corrosion can cause an issue like that.

Still not 100% confident that everything is fixed, but good progress was made. Its fun learning about the workings of this airplane!

Edited August 24, 2016 by Drew_Wagner

[mooniac15u]

Are you sure that you got the right solenoid? Later M20J's had 24V electrical systems. It would be easy to order the 24V solenoid by mistake because that model would be listed as approved for the M20J. 

[Drew_Wagner]

Yes it is definitely the 12V solenoid unless it is labeled incorrectly.

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[ArtVandelay]

There are 3 solenoids: power plug, master, and starter, the second connection on the master should be from the power relay.

[laytonl]

Generally the clock and overhead cabin lights are supplied from the fuse before the solenoid.  Lee

[laytonl]

And cigarette lighter is on the fuse too.

[Drew_Wagner]

Hm, my cigarette lighter doesn't energize until the master is engaged. Could that be a potential issue? 

Quick update this morning: Starter arrived at the shop so I went to fly it back this morning to be installed. Turned on master, power came on and then I went to engage the starter and all electrical power turned off. I turned the key to off, cycled the master and power returned, tried starting and lost all power again. Third time was the charm and it cranked right up. Anyone ever had this happen? I am hoping that since we are replacing the starter that will fix it? Also, where can I order a new master switch online or do I have to go through Mooney. I still am having the wagging ammeter issue and it seems that replacing the master is my next step since I have already cleaned the contacts with no joy.

Edited August 26, 2016 by Drew_Wagner

[mooniac15u]

Have you tested your battery?

[Drew_Wagner]

Yes, battery was on a minder all night and is at 12.9V. Pretty confident it is something down stream.

[carusoam]

Drew,

keep in mind battery health comes in two forms.  Being able to hold the 12.9 V is a good sign, but the battery's capacity might still be off.

At annual the battery gets a capacity test.  A lot of Gill batteries get tossed after two years of low usage...

do you have a separate switch (master) for your instrument panel?

Adding to the confusion is the way instrument master switches are wired.  The normally open vs normally closed modes are used in a way to add protection to the electronics that isn't obvious to the user.

 

when you lose all electricity on start-up, how do you know?  Are all the electronics on? 

 

keep in mind the POH has the electronic wiring diagram for your plane.  You may want to have it ready for your mechanic.

PP ideas.  Not a mechanic.

best regards,

-a-

[Drew_Wagner]

I do have a separate avionics master. When it lost power I could audibly hear the power shut down and the gyros start slowing down just like when you cut the master. Also my JPI is set up on a separate switch downstream from the master and off of my avionics master and it shut down as well.

I am at the shop now and will have them test the battery. Couldn't hurt! Thanks for the suggestion.

Edited August 26, 2016 by Drew_Wagner

[carusoam]

It is a good idea to not have the electronics powered up while starting the engine. This is a really good idea if you are experiencing strange electric issues like over and under voltage, and spikes... Burning up a radio can be expensive...

In the automotive world, they do this automatically.  You can't start the car with the transmission in gear.  In aviation, as PIC, you get to handle all the details...  (In some Mooneys) You can start the plane at full throttle by skipping one step in the start up procedure.

Best regards,

-a-

[Marauder]

Since we are talking about electrical troubleshooting. Can someone remind me what the proper way to determine how much draw the aircraft is pulling while in flight? I am working through an emergency "unloading" checklist and was curious what would be the best way to verify how much juice a piece of equipment is really drawing. Is it just a matter of turning off everything, pulling the alternator field breaker and then adding hardware back in and look at the draw it is showing on the JPI 900?

[Drew_Wagner]

To clarify, I start the airplane with only the master on, avionics master off. But your master does start the gyros rotating and warning lights such as the low vac which illuminates when they are slow before start up. That light alone going off told me the power was lost. New starter is in and it starts like never before, so pretty sure I have one issue fixed. Now onto the fluctuating ammeter...seems to only happen at higher power settings. I flew home 1/2 way at WOT 2500 like I usually fly and when I dropped it to 23 x 23 it seemed to happen less often. My intuition says that tells me the issue is made worse by more vibration and is probably in front of the firewall? Or should I go the replace master route first?

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[ArtVandelay]

You can find the amperage draw in the equipment specs, and it might change based on things like if radio is receiving or not, transmitting will be much more of course, whether you have a VOR tuned to an active frequency, so even measuring with JPI will be an approximation.

[ArtVandelay]

I'm sure there is some vibration in the instrument panel and of course the master switch as well, could be a lose or corroded wire on the shunt. I would spend some quality time checking all connections you can find.

One diagnostic test you can try is to jump the master and see if it fixes your problem, obviously use extreme caution not to short something and make sure it doesn't get hot from carrying too much current.

[carusoam]

As TJ pointed out...

The ammeter is a simple volt meter measuring voltage across the shunt.  Two wires and a simple voltmeter.  Checking it is as simple as it gets...

the shunt is a large ultra low resistance resistor mounted on the fire wall.  The ammeter is actually a voltmeter with it's face painted to reflect amps...

things that die over time...

starters, alternators, voltage controllers, and fuel level sensors. Easy to replace.  Much better (stronger, lighter, accurate) than original.

Best regards,

-a-

[Drew_Wagner]

https://vimeo.com/180363010

Here is a quick video of the issue in action from my flight this morning. Full throttle had just leveled off from the climb.

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