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Ignition confusion

cdeggz

Well Known Member
I’ve been noticing about 50% when I start my plane it starts when I give up cranking and release the key. It’s as if the act of releasing the key from start to “both” is what gets it to finally catch.

I was not sure what the issue was but was due for magneto overhaul, so I switched to dual pmags. I was expecting this to make my engine starting issues go away, but it has gotten significantly worse. I can still get it stated but almost always happens at key release after I give up. After startup everything works as expected.

Troubleshooting steps I have taken:
-Verified during cranking voltage is not dipping too low. I still see 10V on the main bus while cranking
-Started the engine with a different battery on the EI, no difference.
-probed the ignition switch (thinking maybe somehow p-leads were getting grounded in the “start” position). Everything checked out normal.

Any other ideas? It an RV-10 with IO-540-C, fuel injected.
 
I had the same issue with my o-320. The issue turned out to be the left magneto was out of internal adjustment. This was due to wear even though the magneto only had 290 hours on it. The result of the wear and incorrect e gap was that it was trying to fire during start at 13 degrees after TDC and the engine was not catching until both mags were back online. It turned out both were out of adjustment even though they were timed correctly at 25 BTDC. I would suggest that the left mag is probably too retarded but I am not sure exactly what you can do with pmags to change that.
 
Is the jumper on the A-510-2 keyswitch between Terminal 1 and the adjacent GRD lug?
 
I’ve removed the jumper that was previously on there.
 

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That ring terminal on the #1 terminal looks like it's touching the GRD terminal however...

Anyhow - here's my theory - The Left Mag is starting to fail. During start, the the Right Mag is >OFF< during cranking by virtue of the key switch configuration (the jumper or ring terminal touching). Releasing the key turns the Right Mag on and there's enough spin left to fire off the engine.

Of course, that's just a theory...

edit -- what else is connected to the "P Lead" ring terminals? Is that an RPM pick up of some stripe?
 
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Thanks BJ. There is clearance at the ring terminals. That’s an illusion from the image.

I think your theory would be correct on a failing mag (as was my guess) but the issue persisted after installing the dual p-mags.

The other wires coming off the ignition are the pmag mode switch wires. I’m starting the engine in variable mode.
 
Thanks BJ. There is clearance at the ring terminals. That’s an illusion from the image.

I think your theory would be correct on a failing mag (as was my guess) but the issue persisted after installing the dual p-mags.

The other wires coming off the ignition are the pmag mode switch wires. I’m starting the engine in variable mode.

For grins & giggles -- disconnect the p-lead from the pMag green connector (Pin #4) on each unit and try to start it.

Also, invest in some proper ring terminals & crimper -- Look for Tyco/TE PIDG (Plastic Insulated Diamond Grip); Mouser, Digikey, others carry them.
 
Also, invest in some proper ring terminals & crimper -- Look for Tyco/TE PIDG (Plastic Insulated Diamond Grip); Mouser, Digikey, others carry them.

Agree with the above----even if the current terminals are not the problem, it is good to use high quality terminals and tools.

Stein has what you need also.
 
See schematic from emag installation manual. Ignore the the typo ("tack". ugh)...Note the connection of the P-Lead (pin 4)

My question about the other connections to the P-Leads on the key switch (Left Mag - Blue Wire/Yellow Wire, Right Mag - Black Wire/Yellow wire stands.

Just a quick refresher:
The key switch will ground the P-leads when in the OFF position, and will ground the opposite P-Lead (R will ground the L p-lead, L will ground the R p-lead), and if the jumper is installed between Terminal 1 and GRD, the Right P-lead will be grounded when the switch is in the START position.

Connecting something else to the P-leads, *could* cause problems with magneto operation, especially if that connection was a ground path.
 

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Thanks BJ decker. I confirmed with the ohmmeter I have the p-lead grounded when off and when the other side is selected. p-leads are not grounded in both, start, and appropriate L/R is selected.

On the 200 series mags (which I have) it calls for an optional mode switch so one can turn off variable timing. This gets wired to the p-leads through 1k resistors. I keep the mode switch open for now (it won't fire at low RPM in fixed timing mode).
 

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Thanks BJ decker. I confirmed with the ohmmeter I have the p-lead grounded when off and when the other side is selected. p-leads are not grounded in both, start, and appropriate L/R is selected.

On the 200 series mags (which I have) it calls for an optional mode switch so one can turn off variable timing. This gets wired to the p-leads through 1k resistors. I keep the mode switch open for now (it won't fire at low RPM in fixed timing mode).

Ah, my mistake on the type of ignition...

So just for grins and giggles - leave the P-Lead disconnected at the 200's and see if you have the same issue.

As always, treat the engine/propellor as "LIVE" and ready to fire - don't touch the propellor, etc. etc...
 
The fact that the same problem exists with both your old mags and new P mags would indicate a problem outside the ignition itself. I would be looking at the switch or the wiring between the switch and ignition as well as the grounds. The fact that the your measurements don't show a problem is not a 100% confirmation that your switch is working correctly. I would run some temporary wires and switches for the P mags to confirm operation, if unwilling to replace switch.

My first guess is that the switch is intermittently grounding both the L and R mags in the start position (only R should be grounded in start position when working properly).

Larry
 
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My first guess is that the switch is intermittently grounding both the L and R mags in the start position (only R should be grounded in start position when working properly).

A good guess, and probably correct.

However, neither of the mags should be grounded in the START position, except for the Right and ONLY if the jumper is present between #1 and GRD.
 
Thanks Larry and BJ decker. In this case both pmags are starting ignitions so both p-leads should be ungrounded in start and both positions. I agreed that it makes sense to be an issue with the switch. On Saturday I used some alligator clips from the ignition switch to check ground continuity to the L and then the R p-lead. I moved the key and pushed on things and shook things for several minutes trying to find a condition that would show the p-leads grounded, but could not get anything.

I like the idea of alternate switches. I might first just keep the volt meter tied to the L or R p-lead every time I do an engine start for awhile and see what is going on there.
 
Craig------as you are also having alternator issues as posted in another thread, I would look for any common link between the two.

Start with the grounds, my $0.02.

It might be time to bring in someone experienced in electrical systems to take a look at your plane.

Good luck, let us know what you end up finding.
 
A good guess, and probably correct.

However, neither of the mags should be grounded in the START position, except for the Right and ONLY if the jumper is present between #1 and GRD.

Admittedly I have no idea how a Pmag is wired. However, the symptoms tell us that the switch or wiring is somehow preventing the pmags from firing with the switch in the start position. OP needs to fully understand how they are supposed to be wired and then confirm actual continuity. Given the symptoms, intermittent problems MUST be considered. This is why I suggested temporary, bypass wiring to confirm.

Larry
 
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