Electrical issues on RV-6A

This is from a family member. It's a real mind boggler. Wanted to see if the VAF family could help figure this out.

Hi, I could use some input on troubleshooting a problem.

Have an RV-6A which we built.

0-360 Lycoming and a fixed pitch Sensenitch prop.

222 TTSN, 222 SMOH.

Due to life circumstances the plane has not flown for several years.

It has been kept covered in an enclosed hanger and the mice properly fed, so the plane is clean, no varmint damage or nests.

We live in a sparsely populated area, therefore there is no mechanic within 120 miles. We can get one to come, and we will if necessary, but would like to try to solve this on our own if possible.

A few years ago the plane began to be hard to start. Troubleshot and it seemed to be the left magneto, and impulse coupler problem. Removed the mag, took it to a licensed mechanic who determined that indeed it was not working. We bought a factory new mag and did have a licensed mechanic come and time it and got the engine going.

Tried to start it a short time later and plane wont start. Got the mechanic again to help troubleshoot. It was determined at that time that the ACS key start switch, #A-510-2, was not working right. The plane would only start with the ground wire to the left magneto removed.

Ordered another ACS keyed start switch. Same model. Installed per schematic. Installed the diode wire on the solenoid indicated as our plane has a two solenoid setup.

Engine will not start.

Then we unhook the ground wire to the left mag and it starts fine. I have not been running the engine up hard, only to about 1200 RPM. There is no indication that it will not develop full power, I just haven?t been testing it at higher. You will see my reasoning as you read farther.

With Left Mag ground wire unhooked:

Go to Right Mag: Slight drop

Go to Left Mag: Slight drop??? With ground wire off it should not drop at all?

After running the engine a minute, we shut down. Hook the left mag ground wire back up.

Now the left mag is hooked up ?properly?

Engine warm now starts, but it starts at that moment, after you decide that it won?t start, and you release the key from the start position. that?s when it fires up.

Run up only to about 1200 RPM,

Go to Right Mag : Slight Drop

Go to Left Mag: Engine DIES instantly.

Flip back to both, it resumes running.

When we built our plane, the one thing that we had done by another person, was the wiring. We installed the instruments but had a retired Air Force avionics technician do all the electrical.

Before all of our challenges referred to above, the plane did have what I would call ?hot mag? issues. My meaning to that is that, like my instructor taught me, before shutting down, idle the plane, and quickly shut off/on the ignition. Properly grounded, the engine should momentarily die. Ours sometimes would, sometimes not, so there has probably been an issue right from the beginning.

If someone can give us some ideas on what is going on and how to fix this, we would be most grateful. I have tried to give all the info that we have learned so far. Any ideas, or if pictures might help, I can take some.

As a different but related question, Is there a good electronic ignition system for this engine. Laser, Light Speed, etc?

Thank you!

Switch

I think the best thing to do is disconnect all wires and test each part by itself.
I'd first test the switch. Assumes you have a impulse mag on the left side of the engine, left side as you are sitting in the cockpit.
Test the switch first with out wires attached if possible.
Turn switch off, both right and left mags are grounded.
Turn switch to left, left mag open, right mag ground.
Turn switch to right, right mag open, left mag ground.
Turn to both, both right and left open.
Turn to start, left mag open right mag ground.
Then check the wires to each mag, not hooked up to anything.
Both wires should be open, no shorts to ground, this could happen if using shielded wires and get one grounded.
Make sure right wire goes to right mag, then do left.
Mark wires then hook up to correct terminal on switch.
Try it and hopefully will work.
Good luck. Bob

First, by Mag ground wire, I assume you mean what is called the "P lead", not the shield covering the P lead wire. But check that the shielding is attached to ground.

Pull back the rubber boots on the P lead connections to the mags. Label and disconnect the wires.
Master off, turn switch to L, use an ohmmeter to verify the right (co pilot side) mag's P lead is shorted to ground, and the left is not.
Repeat for the switch on R, left mag P lead should be grounded, right not.
Repeat for the switch held to Start (make sure the master is off!). R mag lead should be grounded, left mag lead should be not grounded.
Switch off, both mags' P leads should be grounded.

I would repeat these tests several times to make sure the switch is not intermittent.

DO NOT TURN THE PROP DURING THESE TESTS. DO NOT TURN THE MASTER ON.

EDIT: I see "other Bob" wrote first. Either his way or mine. Choose whether it's easier to get to the switch or to the mags, as to which way to do first.

thank you for the quick reply.
we did do some checking with a tester yesterday, but will go out shortly with a better tester.
will make notes and let you know what we learn.

Make sure you disconnect the P leads,either at the mag or the switch. Depending on where the points are in the cycle, the mag may read 0 ohms even when "hot".
Do not turn the prop.

Replace

Since you don't exactly know what the wiring is, it might be easier to simply replace all of the P-lead/switch wiring.

Borrow a shrink tube labeler and mark all of your new lines...

There are not that many wires involved.

Mag?

Had the same problem with a new RV, what we found, after replacing the mags, (thought it was internal) the "P" lead to the L mag would short out when it was attached to the mag, and was not shorted when it was off, so a bit of twisting of the wire would cause the short only if it was on the mag, so it would test OK off of the mag. The switches do fail a bit, in my RV's I use 2 toggles and a push button for start and lock the canopy and throttle. Much more reliable and much less expensive. You might replace the "P" lead with a temporary wire just for a test, and totally remove the old one at both ends, at the switch and the mag. It doesn't need to be shielded for a test.

RT

Benneal do you happen to use bendix mags? Theses mags are internally grounded so you don't want to ground the shield to the magneto casing as you would on a slick mag. I had the same issue as you and once I took the shield ground off of the mag case everything works as designed. FWIW.

Good luck,
Bill

problem solved

Hi everyone,
Took a helper and a tester and went to chase the wiring. We tested all wires and the ignition switch.
To make a long story short, the left magneto P lead showed continuity to everything.
So there is evidently a defect of some kind in the wire.
We made a jumper from starter switch to the mag, for the left mag.
the engine started great.
mag check normal,
So life is good.
Going to get a new piece of shielded wire tomorrow and make a permanent replacement.
thanks to all for your advice and help. So much appreciated

benneal said:

Hi everyone,
Took a helper and a tester and went to chase the wiring. We tested all wires and the ignition switch.
To make a long story short, the left magneto P lead showed continuity to everything.
So there is evidently a defect of some kind in the wire.
We made a jumper from starter switch to the mag, for the left mag.
the engine started great.
mag check normal,
So life is good.
Going to get a new piece of shielded wire tomorrow and make a permanent replacement.
thanks to all for your advice and help. So much appreciated

Click to expand...

Probably not a defect in the wire, but a defect in how the shield is connected.

My previous comment stands, since you don't know exactly how those shields were physically connected, just replace both of the P-Leads.

I want to clarify something I wrote wrong earlier.
the P lead wire on the left mag is not shielded. so I will be putting on unshielded wire.

so again many thanks to you folks for the great input.

benneal said:

I want to clarify something I wrote wrong earlier.
the P lead wire on the left mag is not shielded. so I will be putting on unshielded wire.

so again many thanks to you folks for the great input.

Click to expand...

Why?

Standard practice is for that lead to be shielded, why not follow the standard?

Sorry that I am kind of dense on this subject. As I stated at the start, the electrical is the one thing on our plane that we had done, so I am really at square one.
I understand that the left mag should use shielded wire.

For some reason the avionics tech did not put shielded wire on it originally.
For what reason would the guy not have used shielded?

So I will run a new shielded wire since that seems to be the right way to do this.
My left mag is a Continental (Bendix?) and William points out that I should not ground the shielding to the mag itself.
So where do I ground the shielding?
Do I pull the shielding away from each end of the P lead? and put on a connector, or just on one end and then ground it to the frame.?

The left mag connection is a threaded pin, on the mag.

I think I am starting to catch on, so just need to know where the shielding attaches on each end.