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RV-7 IO-360 Thunderbolt with dual P-Mags. AOG FIXED!

toolmanmike

toolmanmike

Well Known Member
Friend
IO-360 Lycoming Thunderbolt with AVstar Fuel injection, Deul Pmags.
53 hrs TTSN

I have had absolutely no starting issues for the first 50 hrs of flight. Hot, cold, flooded , etc. 1 Crank and she is running! Only issue was a significant backfire about 3 months ago during Phase 1. Checked out and all was fine.

2 weeks ago I did my 50 hr oil change and inspection:
Oil and filter with sample
New NKG plugs (even though the old ones looked fine)
Tighten and inspect all firewall forward areas. Nothing to note here.

fired right up and flew a few laps around the pattern- put it in the hanger.

1 week ago on a very hot and beautiful Saturday I was giving rides to my neices and nephews. 20-25 min each and I was on ride 6 when the plane just wouldn't start. I tried every trick in the book. No fire. So, I left it for about 5 hrs to cool down. Tried again- no good. I tied it down and left it overnight.

The next day I took the cowlings off and checked the plugs, P-mags, compressions and fuel flow. All good at first glance including p-mag timing. Still wouldn't start. Eventually, I got it to fire by some magic jockeying of the throttle which I can never reproduce. It ground tested fine- thinking maybe I blew out the bad- I shut it down and put the cowls back on. I left the plane till evening time when it was cooler and after MUCH cranking- got it fired again and flew it home 10 minuets. It flew great and no issues until I shut it off at my hanger. No start again.

4-5 days go by and and it fired right up and I flew it 4-5 landings then taxied to the fuel farm. Wouldn't start when warm. I took off the cowls, plugs, leads, etc and couldn't find anything wrong. Let it set in the hanger overnight.

Next day it wouldn't start. Not Hot, Not flooded. Just cranks. I changed the plugs back to the old ones with 49 hrs on them.- no change.

Now Im serious! I took the cowls off again and me and my A&P really got into it. We checked P-mag indications according to the "trouble shooting" guide at emag.com. We checked compression, I took out the fuel injectors and did a flow test diagnostic according to Lycoming. Everything checks out fine. We even tried starting fluid and didn't even get a pop. I am baffled. I am leaning toward the mags thinking they got hot and something inside went bad but all diagnostics that you can do in the field check out just fine. I did re-time the mags just in case. no change.

It has now been 2 weeks and I still don't have a solution.

Has anyone had a p-mag go bad with no external indications? The timing is showing good. The "pull through" test is working as it should. No LED indications of a fault. I do have 5 phone calls and an email into emag but nothing back from them yet.

HELP!
 
My dad always said... if it won't start it's either fuel or spark (or both). I'll assume you tested fuel, to and thru the injectors? If so, then you didn't mention is this a dual p.mag setup? If so, seems odd that both would fail. I'm not an expert, but is there a way to ground a line on the p.mag and check it's function with or without the battery? e.g. don't they need battery to start, and then will run with or without battery? Might this power need be missing somehow? I'll set back and get educated as I'm sure I got most of what I said wrong... but it's one or the other (or both) I'm pretty sure.
 
Just a guess from the cheap seats, but I’ll bet a beer it’s a ground and/or power wiring issue to your Pmags. And double or nothing it’s the ground. In your electrical system, do they share a common ground? Are the terminals secure? Chase those wires in excruciating detail and put a meter on the them. Good luck.
 
Can you describe your start procedure? When cold and when it is hot

I have an io-360-1mb engine over 150 Sn and have found the engine doesn’t start as crisply as before.

Cold start. I set mixture to rich and prime for 4secs. Set to idle cutoff. Before it would start in this position but now, I had to move the mixture to slight greater than ICO, throttle to 1/2 inch and then would catch.

Hot start seems to be more normal. Throttle to about 1/4 and move mixture to rich when the engine catches

Edit: I did run up check and everything was okay. I did the flight test and TAS at cruise was normal as before. Looking for answer as well.
 
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toolmanmike said:
Has anyone had a p-mag go bad with no external indications?

HELP!
Click to expand...
I feel your pain.

So to recap:
  • Ran great for 53 hours
  • Always started on one blade
  • After a 5 ride sortie, engine didn't want to start even after leaving it overnight to cool down.
  • Fuel Injection flow test passed
  • Timing looked good but retimed mags
  • Swapped out spark plugs
  • No fault lights showing on p-mags
  • Pull through test shows spark plugs firing (Did you do the pull through test on 4 plugs or just 1?)
  • Next to impossible to start
  • When it does start, the engine performs normally (Can you confirm that no anomalies identified during mag check?)
To answer your question .... After running dual p-mags for over 15 years I did have one fail intermittently. Engine started, mag check showed right mag inop. Could not get it online. Flew short flight to home base where I pulled off the runway and did a mag check that showed right mag was operating normally. Pulled the cowl checked timing, plugs, cable resistance, etc. Did a runup and could not get it to fail. It took me a few hours of several starts, stops, etc to get it to fail again. Sent it back to Emag who found that the circuit board needed replacement. However, in your case I think the chances of both P-mags failing simultaneously, is very very slim.

What is puzzling about your situation is that you have confirmed fuel delivery and spark is occurring as it should. What do the plugs look like after a failed starting attempt? If the fuel was bad I would expect that the engine would not run normally after you got it to start. Likewise if the fuel/air mixture was compromised I would expect that this would have been identified in you short flight.

I will say that during the past 15 years support from Emag has been nothing short of superb. In my experience, they have always been responsive and helpful.

Do let us know how you finally resolve this issue. Feel free to PM if you you would like to discuss further.
 
drill_and_buck said:
I feel your pain.

So to recap:
  • Ran great for 53 hours
  • Always started on one blade
  • After a 5 ride sortie, engine didn't want to start even after leaving it overnight to cool down.
  • Fuel Injection flow test passed
  • Timing looked good but retimed mags
  • Swapped out spark plugs
  • No fault lights showing on p-mags
  • Pull through test shows spark plugs firing (Did you do the pull through test on 4 plugs or just 1?)
  • Next to impossible to start
  • When it does start, the engine performs normally (Can you confirm that no anomalies identified during mag check?)
To answer your question .... After running dual p-mags for over 15 years I did have one fail intermittently. Engine started, mag check showed right mag inop. Could not get it online. Flew short flight to home base where I pulled off the runway and did a mag check that showed right mag was operating normally. Pulled the cowl checked timing, plugs, cable resistance, etc. Did a runup and could not get it to fail. It took me a few hours of several starts, stops, etc to get it to fail again. Sent it back to Emag who found that the circuit board needed replacement. However, in your case I think the chances of both P-mags failing simultaneously, is very very slim.

What is puzzling about your situation is that you have confirmed fuel delivery and spark is occurring as it should. What do the plugs look like after a failed starting attempt? If the fuel was bad I would expect that the engine would not run normally after you got it to start. Likewise if the fuel/air mixture was compromised I would expect that this would have been identified in you short flight.

I will say that during the past 15 years support from Emag has been nothing short of superb. In my experience, they have always been responsive and helpful.

Do let us know how you finally resolve this issue. Feel free to PM if you you would like to discuss further.
Click to expand...
Thank you for your reply. Yes to all the above.
Checked pull through test with all 8 plugs and all fired. Changed plugs and they fire also. Fuel flow is good.

No offense to well wishers but this is not a start procedure debate. I have been running this engine for the last 50 hrs with no starting issues. That being said- I have also tried every option I have read here and elsewhere. It just won’t start. Hot or cold.
Stumped. Still waiting for meat to get back to me.
 
This is a puzzle. Is your timing correct per Pmag instructions? A 20 degree btc motor should be timed a few degrees AFTER TC when using pmags. Make sure you’re looking at the correct line on the starter ring. My second thought is perhaps the start timing retard feature within the pmags isn’t working correctly. In other words your pmags are firing 25 degrees advanced during start. If possible beg to borrow a spare set just to rule them out.

For what it’s worth pmag has gone radio silent for my recent request. I’ve been battling kickback issues and was hoping for a little help on their end. I ended up solving the issue myself via timing adjustments.
 
You need 3 things to make it go bang. Fuel, Spark & Air. Looks like you guys have spark, at least during the pull through test. You said you pulled the injectors and they flow good, right?

So what did you touch during your 50 hour & oil change? When you checked the filter screen did you maybe change something in the mixture control linkage? You make a mess when you change oil and the filter is right above the mags. Did you get oil in those cheesy electrical connectors that Emag uses? How's the induction system? Is the air filter okay?

If it were me, at this point I'd start looking at stuff like that

edit- I think the backfire you mentioned in your first post is a red herring. emags are a wasted spark system. They fire 1&2 as a pair and 3&4 as a pair. If you've overprimed you can get an afterfire through the exhaust because it will pop off that cylinder when the exhaust valve is open. Thats not the same thing as a backfire up through the induction system.
 
toolmanmike said:
Thank you for your reply. Yes to all the above.
Checked pull through test with all 8 plugs and all fired. Changed plugs and they fire also. Fuel flow is good.

No offense to well wishers but this is not a start procedure debate. I have been running this engine for the last 50 hrs with no starting issues. That being said- I have also tried every option I have read here and elsewhere. It just won’t start. Hot or cold.
Stumped. Still waiting for meat to get back to me.
Click to expand...
Any chance this is a horizontal induction engine like a IO-360-M1B ?, Is there a sniffle valve installed, have you raised the tail to level and observed the sniffle valve exit point. These engines are well known for collecting large amounts of raw fuel in induction system quickly during certain starting conditions AND this large amount of fuel remains in the aft recesses of the induction area because of the tail down angle & fwd sniffle valve position. This over rich condition can cause such a rich mixture that it will never fire. Backfires are known to have caused great damage at times. You can also inspect by removing air inlet to FI servo & open throttle plate & use a borescope. Takes a long time - many days+ for a flooded induction area to have the raw gas evaporate especially if throttle is closed not allowing ventilation.
Just a thought - worth a look see...
 
toolmanmike said:
Eventually, I got it to fire by some magic jockeying of the throttle which I can never reproduce.
Click to expand...
Never had a pMag fail over 20+ years of service.

The point you made on “magic jockeying”, combined with this happened after maintenance, may indicate you have a gross air leak in the fuel line. What else did you open on this inspection?

One other thing to check. The pMags are grounded to the engine not the ship ground, correct?

Carl
 
Carl Froehlich said:
Never had a pMag fail over 20+ years of service.


Carl
Click to expand...
And we have had a completely different experience. 4 previous issues (bearings, alternator phase failure, bad board) and the now 5th failure. Occurred at 300 feet on takeoff - loss of power, rough running. Fortunately, the EI Commander had been providing a clue which pMag was the likely culprit. The pilot (my son) turned off the errant pMag and the engine immediately recovered. Engine and airframe has about 500 hours.

Engine was balanced upon IRAN at Penn Yan and we dynamically balanced the prop to 0.03 ips.

We’ve now ordered SDS CPI-2 to replace the dual pMags.
 
Carl Froehlich said:
Never had a pMag fail over 20+ years of service.

The point you made on “magic jockeying”, combined with this happened after maintenance, may indicate you have a gross air leak in the fuel line. What else did you open on this inspection?

One other thing to check. The pMags are grounded to the engine not the ship ground, correct?

Carl
Click to expand...
Good suggestions. I did not touch the fuel system at all on the previous maint. But have been back over it all since with that same thought in mind. No leaks. Pmag are grounded to the engine- yes. Thank you for your response. They pass the power and ground test also- so it is not a matter of them not powering up. I have spark. Just not sure about why I don’t have any combustion.
 
Carl Froehlich said:
Never had a pMag fail over 20+ years of service.

The point you made on “magic jockeying”, combined with this happened after maintenance, may indicate you have a gross air leak in the fuel line. What else did you open on this inspection?

One other thing to check. The pMags are grounded to the engine not the ship ground, correct?

Carl
Click to expand...
Also, it did happen after the maintenance but not right away. I flew and started the plane just fine for 7 flights. On the 8th it just wouldn’t go. Then I got it to start after much “jockeying “ then it wouldn’t. Then it did. Now nothing I do will get it going. Not even a backfire.
 
AZSteve053 said:
Any chance this is a horizontal induction engine like a IO-360-M1B ?, Is there a sniffle valve installed, have you raised the tail to level and observed the sniffle valve exit point. These engines are well known for collecting large amounts of raw fuel in induction system quickly during certain starting conditions AND this large amount of fuel remains in the aft recesses of the induction area because of the tail down angle & fwd sniffle valve position. This over rich condition can cause such a rich mixture that it will never fire. Backfires are known to have caused great damage at times. You can also inspect by removing air inlet to FI servo & open throttle plate & use a borescope. Takes a long time - many days+ for a flooded induction area to have the raw gas evaporate especially if throttle is closed not allowing ventilation.
Just a thought - worth a look see...
Click to expand...
This is a vertical induction but it still holds a fair amount of fuel in the intake. I hadn’t thought of pooling fuel staying in the intake for days! I shall look into it. BUT, even with a rich mixture - with sufficient cranking at idle cutoff- I should be seeing something.
 
Desert Rat said:
You need 3 things to make it go bang. Fuel, Spark & Air. Looks like you guys have spark, at least during the pull through test. You said you pulled the injectors and they flow good, right?

So what did you touch during your 50 hour & oil change? When you checked the filter screen did you maybe change something in the mixture control linkage? You make a mess when you change oil and the filter is right above the mags. Did you get oil in those cheesy electrical connectors that Emag uses? How's the induction system? Is the air filter okay?

If it were me, at this point I'd start looking at stuff like that

edit- I think the backfire you mentioned in your first post is a red herring. emags are a wasted spark system. They fire 1&2 as a pair and 3&4 as a pair. If you've overprimed you can get an afterfire through the exhaust because it will pop off that cylinder when the exhaust valve is open. Thats not the same thing as a backfire up through the induction system.
Click to expand...
You are correct on the cause of the backfire. But that was literally months ago. Plane has flown well for many hrs since. I shall take it into advisement though. Thanks.
 
The only ‘common’ thing to both pmags for starting is power and ground. You may want to check voltage at the pmag while cranking.
See page 13 of the manual regarding voltage requirements during starting.
 
Sounds like intermittent no spark. When all else fails, go back to the basics. You confirmed timing but didn’t confirm the plugs are actually sparking. Pull a plug, connect the plug wire back on and use a wire to ground the base and crank the engine while looking for a spark. My money is on a bad ignition switch or wiring to it. Not a big pmag fan, but the likelihood of two of them failing intermittently in tandem seems implausible. You should also confirm that the ignition is wired to have both live on start. Could be wired wrong and one is failing intermittently.
 
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toolmanmike said:
This is a vertical induction but it still holds a fair amount of fuel in the intake. I hadn’t thought of pooling fuel staying in the intake for days! I shall look into it. BUT, even with a rich mixture - with sufficient cranking at idle cutoff- I should be seeing something.
Click to expand...
Fuel won’t last but minutes in the open air.
 
Possibly voltage drop: Look carefully at the design of how you have +12V getting to the Pmag as well as the health of your battery. I had a no spark issue on a PMag equipped RV-10 appear after previously having years of no issue. It began when I had just added a back up generator and I suspect in my case it was just enough additional mechanical load on the starter motor that the additional current draw was causing the voltage drop to be greater than the pmag was willing to accept. I spoke with Emag support. He said that they have seen cases where the input voltage for the system to fire was too low when cranking in some cases. He suggested that voltage in the feed from the battery may be dropping too much on cranking due to the large current in the positive cable that runs from the master contactor to the startor solenoid. Since this also feeds the main bus. everything on it, including the ignition sees that voltage drop. And this is worse in 10's with a long run from a rear mounted battery. I ended up running a small separate wire from the main contactor to the ignition that didn't have the starting current going through it. Problem solved. For added margin I also used it as an excuse to upgrade my Odyssey to an Earthx that has a higher resting voltage.
 
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Sure you didn't leave a rag in the throttle body? Also, you mentioned that you didn't open up the fuel system - perhaps it would be wise to check the fuel filter(s)?

Check all common elements - how are your pmags wired? Single key switch or individual toggle switches? What kind of battery?
 
dadjokes said:
Possibly voltage drop: Look carefully at the design of how you have +12V getting to the Pmag as well as the health of your battery. I had a no spark issue on a PMag equipped RV-10 appear after previously having years of no issue. It began when I had just added a back up generator and I suspect in my case it was just enough additional mechanical load on the starter motor that the additional current draw was causing the voltage drop to be greater than the pmag was willing to accept. I spoke with Emag support. He said that they have seen cases where the input voltage for the system to fire was too low when cranking in some cases. He suggested that voltage in the feed from the battery may be dropping too much on cranking due to the large current in the positive cable that runs from the master contactor to the startor solenoid. Since this also feeds the main bus. everything on it, including the ignition sees that voltage drop. And this is worse in 10's with a long run from a rear mounted battery. I ended up running a small separate wire from the main contactor to the ignition that didn't have the starting current going through it. Problem solved. For added margin I also used it as an excuse to upgrade my Odyssey to an Earthx that has a higher resting voltage.
Click to expand...
I do have the Earthx battery and it cranks strong. I have checked the plugs as the engine cranks and they are sparking. Voltage at the meter is showing 13+ at rest and 11+ while cranking. Ground has also been checked. Haven’t tried a meter at the pmag harness yet while cranking. Will do.
 
rv8ch said:
Sure you didn't leave a rag in the throttle body? Also, you mentioned that you didn't open up the fuel system - perhaps it would be wise to check the fuel filter(s)?

Check all common elements - how are your pmags wired? Single key switch or individual toggle switches? What kind of battery?
Click to expand...
All done. No obsructions and fuel filter was checked. Remember- fuel flow test per Lycoming was completed at the injectors. All good.
 
Sounds to me like your spark isn't retarding to start. I've run Lasar mags, mine do not have impulse couplers to retard the spark, for 20 years and once my voltage drops a bit too much It'll crank fine but just will not fire. I read up a bit on your earth x and they don't want you to jump them. Given all you have tried I'd disconnect the battery leads to the earth x and jump it to a different battery. If it starts you've found your problem. I know nothing about P mags but I'm guessing it's not retarding the spark due to low voltage.

N801SM
Flying since 2001
 
Are you running the PMags on an ACS Ignition Switch? Or the preferred Push Button starter, with separate power to the PMags? This sounds like a voltage/amperage drop when cranking. The PMags need good 12volt power below 800 RPM
 
toolmanmike said:
I have checked the plugs as the engine cranks and they are sparking.
Click to expand...
Fuel, air, spark.

Compression can't reallty be an intermittent thing, so we have fuel and spark. May be worth pulling an injector line and observe flow while cranking. Intermittent issues like this are not common on mechanical FI, so I would still be focused on ignition. Though there could be some blockage issue in the fuel system that only appears some times. You know that it is sparking, but don't really know where in the cycle it is spaqrking. I once fixed an issue for a buddy that the A&Ps couldn't fix. They screwed up the mag assembly process and it was sparking 180* out of phase.
 
lr172 said:
Fuel, air, spark.

Compression can't reallty be an intermittent thing, so we have fuel and spark. May be worth pulling an injector line and observe flow while cranking. Intermittent issues like this are not common on mechanical FI, so I would still be focused on ignition. Though there could be some blockage issue in the fuel system that only appears some times. You know that it is sparking, but don't really know where in the cycle it is spaqrking. I once fixed an issue for a buddy that the A&Ps couldn't fix. They screwed up the mag assembly process and it was sparking 180* out of phase.
Click to expand...

Fuel, air, spark, compression. Like you said compression isn't really intermittent so that leaves the other three. He's checked the fuel flow already. That leaves air and spark presence and timing.

This seems maintenance induced. Has anyone checked the intake for a rag or a mouse nest?
 
My money is on the P-mag harnesses. P-lead, power & ground. Doubtful both would have a problem at the same time, but maybe there's a common point in the harnesses. I would trace the wires and check the connections. The P-mag connector is known to have issues. I used ferrules on the wires. Maybe it has good connections till the engine turns over.
 
N40ES said:
Are you running the PMags on an ACS Ignition Switch? Or the preferred Push Button starter, with separate power to the PMags? This sounds like a voltage/amperage drop when cranking. The PMags need good 12volt power below 800 RPM
Click to expand...
I agree - something strange in the way the mags are wired up, or an issue with a key switch. Can you include a diagram on how you wired the pmags?
 
wirejock said:
My money is on the P-mag harnesses. P-lead, power & ground. Doubtful both would have a problem at the same time, but maybe there's a common point in the harnesses. I would trace the wires and check the connections. The P-mag connector is known to have issues. I used ferrules on the wires. Maybe it has good connections till the engine turns over.
Click to expand...
i agree 100% it is worth checking the wiring of the ign switch, as it could be wired to start on one pmag only in which case there could be an issue with one of them.
 
lr172 said:
i agree 100% it is worth checking the wiring of the ign switch, as it could be wired to start on one pmag only in which case there could be an issue with one of them.
Click to expand...
I think we are getting somewhere! Consensus here is pmag related wiring and or voltage. That is EXACTLY what I was told just now by the EMAG people. Sometimes the voltage is fine for the pull through test but when cranking it can dip below acceptable levels for the pmags. This causes them to “turn off” until voltage comes back up. I, off to check my battery health, get a good volt meter on the harness and check while cranking and some other tricks. Thanks to those who have input thus far. Will report back.

FYI fuel flow was checked while cranking and yes- plugs are wet after cranking. Narrowing it down to Majik electricity!
 
Based on a recent experience with a friend who has electronic ignition (not PMag), after much trouble trying to get started at an airport far from home, we added charge to the (old) EarthX battery andbot started and we got home. He now has a new battery and the problem went away.

Same plane many years ago, a certain supplier was emphatic that the system in use as that time would fire at a certain low voltage. We instrumebted the system and showed that at start, the battery dipped VERY LOW even though it was cranking the engine just fine.
 
Another way to determine if the problem is low voltage is to pull the breaker/fuse powering one of the PMAGs and connect a 9V battery to power that PMAG. Then see if engine will start. If it does start, recommend disconnecting the 9V battery before resetting the breaker or reinstalling the fuse.

Regards,
Roy
 
dadjokes said:
Possibly voltage drop: Look carefully at the design of how you have +12V getting to the Pmag as well as the health of your battery. I had a no spark issue on a PMag equipped RV-10 appear after previously having years of no issue. It began when I had just added a back up generator and I suspect in my case it was just enough additional mechanical load on the starter motor that the additional current draw was causing the voltage drop to be greater than the pmag was willing to accept. I spoke with Emag support. He said that they have seen cases where the input voltage for the system to fire was too low when cranking in some cases. He suggested that voltage in the feed from the battery may be dropping too much on cranking due to the large current in the positive cable that runs from the master contactor to the startor solenoid. Since this also feeds the main bus. everything on it, including the ignition sees that voltage drop. And this is worse in 10's with a long run from a rear mounted battery. I ended up running a small separate wire from the main contactor to the ignition that didn't have the starting current going through it. Problem solved. For added margin I also used it as an excuse to upgrade my Odyssey to an Earthx that has a higher resting voltage.
Click to expand...
I had a very similar issue. In my case it was a starter going bad. It continued to crank the engine OK, but was pulling too much current to let the pmags fire. At first replaced the Odyssey with an EarthX and that "fixed it" for a few weeks. When it happened again, the starter was replaced and since then (2ish years) it's been working fine.
 
Roy Thoma said:
Another way to determine if the problem is low voltage is to pull the breaker/fuse powering one of the PMAGs and connect a 9V battery to power that PMAG. Then see if engine will start. If it does start, recommend disconnecting the 9V battery before resetting the breaker or reinstalling the fuse.

Regards,
Roy
Click to expand...
Beat me to it. Power the P-mag circuit with another battery. Now I wonder about the starter.
 
toolmanmike said:
I think we are getting somewhere! Consensus here is pmag related wiring and or voltage. That is EXACTLY what I was told just now by the EMAG people. Sometimes the voltage is fine for the pull through test but when cranking it can dip below acceptable levels for the pmags. This causes them to “turn off” until voltage comes back up. I, off to check my battery health, get a good volt meter on the harness and check while cranking and some other tricks. Thanks to those who have input thus far. Will report back.

FYI fuel flow was checked while cranking and yes- plugs are wet after cranking. Narrowing it down to Majik electricity!
Click to expand...
You said you measured 11 volts while cranking. That is more than adequate.

Get a wiring diagram for the ignition switch and ensure you are not grounding one of the p leads on start. I would also bypass the ignition switch for testing. Pull the two p leads off the switch. You can shut down with mixture ico.
 
wirejock said:
OP said the plane performed fine for five flights then failed on the sixth. He didn't change anything between.
Click to expand...
I read that it had a problem after all the plugs were changed.... Can't assume anything....
But OK that's fine. Any chance the plugs that were changed were the wrong kind?
 
I had a similar experience with my -10.

Walt and some others hit on it....bus voltage during start. My symptoms also started after 40 hours or so.

You can't see it clearly on most monitor systems, but if your battery(s) are getting to be something other than brand new, your bus voltage can easily drop below 10V for that split second that the starter is pushing a piston thru its compression stroke. That is the same time when the PMAG is preparing to fire a spark (TDC for starting). If the ship's voltage to the PMAG drops much below 10 volts, NO SPARK IS SENT.

I bet $5 that your "backfire" was a spark (waste type) that actually fired AFTER you released the start switch when the voltage returned north of 10 volts.

Find a 12v source of some kind that's not the aircraft battery and directly power a PMAG for a starting test. Make sure that test battery is powering only the PMAG and not back feeding anything. If it fires right up regularly, you have found the culprit.

I have spoken with Brad at EMAG about this issue. I was hoping they could design a capacitor with a diode setup to keep the voltage up on these things for start, but no luck.

My first attempt at a fix was to power my panel buses directly from the battery contactor using a #6 wire versus taking it from the side of the engine starter solenoid. That raised the panel voltage some at start, but the problem still existed intermittently.

My next solution was to put a receptacle under the instrument panel that would accept a plug from a cheap power pack of 8 AA batteries found on Amazon. This directly powered a PMAG. (Remember to turn ship's power off when starting so that your battery pack is supplying power only to the PMAG.) After start, unplug the battery pack and turn on ship's power.

After a while I went with a more permanent solution...I put the PMAG ship's power on a "Conditioned Bus" that is powered by a TCW unit that keeps that bus powered at 12V during start. No problems since.
 
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JDA_BTR said:
I read that it had a problem after all the plugs were changed.... Can't assume anything....
But OK that's fine. Any chance the plugs that were changed were the wrong kind?
Click to expand...
Or perhaps the new plugs are Chinese counterfeit NGK BR8ES?
Did the OP check each plug electrode resistance to be ~4K ohm?

People experiencing such severe buss voltage drop on start is something that has never happened to me, but I’m cranking on two PC-625 batteries and no backup batteries. The SkyView display does not even blink on startup.

Carl
 
Yes, I have a teammate who had similar issues and eventually determined that one of the fine wires that attach to the P-Mag was loose. It made enough contact to start intermittently and once running it was fine. He thought he had it fixed then on landing once the rpm was low enough to no longer create its own spark it died. This lead him to look at the incoming wires and sure enough one of the screws backed out.
 
Kaos2800 said:
Yes, I have a teammate who had similar issues and eventually determined that one of the fine wires that attach to the P-Mag was loose. It made enough contact to start intermittently and once running it was fine. He thought he had it fixed then on landing once the rpm was low enough to no longer create its own spark it died. This lead him to look at the incoming wires and sure enough one of the screws backed out.
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Also on this note, really inspect any shielded wires, use a magnifier, those fine wires can make contact and cause grief. Move the shields further back and isolate with shrink. We spent hours troubleshooting a problem where just one of those accidentally making contact, couldn't even see it without using magnification and a light. Sometimes it would be an issue, other times not sure much, however, once it was reterminated, no more issues.
 
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