WaynePierce

Left mag check kills engine

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On 11/15/2018 at 2:41 PM, WaynePierce said:

Update... last weekend I took the advice from many of you and set the JPI 800 to a two second interval, pulled the plane out of the hangar, started it and after it had warmed up did a normal mag check everything was fine and I left it on the separate mags for probably 15 second to get a good reading on the JPI. The second time the engine died on the Left (switch set to "R") and proceeded to restart knowing I had captured the information! It acted more or less normal on the next two tries. Shut it down and pushed it back in to the hangar, ensuring I was on my new tape marks and the vertical stab was lined up with the Green tape in the center of the back of the hangar. ;) Then downloaded the information from the JPI and took it home to find somehow I didn't record everything and didn't have the engine quitting. Probably because I only downloaded the last thing it recorded. When the engine quit it might have started a new recording so I only had from the restart.

Anyway fast forward to Tuesday and my A&P and I drove down to the plane in the afternoon, pulled it out and he went through the same thing and it stuttered, didn't die though, but enough to know what I was talking about. He checked the P-leads and all the wires everything checked good, we took the Mag off and unfortunately it all looked good as well. He was going to check the coils and cap's back at his shop. I haven't heard back from him. When he was doing the run up, he tried to move the key around in the switch to see if it would react to it but it didn't.

More next time...

Wayne, when you download from the EDM, the two options are "All" or "New". If you select "New", it downloads everything since the last time you downloaded, so you should have captured the initial run as well as the restart. While it may be two files, you should be able to look at them and see something happening at the end of the first file. If you uploaded everything to Savvy, you should see multiple flights recorded for the day in question.

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On ‎11‎/‎15‎/‎2018 at 12:41 PM, WaynePierce said:

Anyway fast forward to Tuesday and my A&P and I drove down to the plane in the afternoon, pulled it out and he went through the same thing and it stuttered, didn't die though, but enough to know what I was talking about. He checked the P-leads and all the wires everything checked good, we took the Mag off and unfortunately it all looked good as well. He was going to check the coils and cap's back at his shop. I haven't heard back from him. When he was doing the run up, he tried to move the key around in the switch to see if it would react to it but it didn't.

More next time...

Ask him if he has the gear to bench test the mag.  Either that, or reinstall the mag, disconnect the ignition harness at every spark plug, and hold each spark plug wire near a chassis ground to see how far you can get it to spark while cranking (CAREFULLY, of course).  That will tell you how strong the left mag is, assuming that is the mag in question.  It won't tell you anything about the right mag, though, since it has no impulse coupling.

Oooh, I just realized this applies to the IO-360 A3B6 with the two Slick mags, but I forget which mags have impulse couplings in the A3B6D dual mags...  Bench testing should work the same with either, though, they can spin the mags fast enough on the bench.

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1 hour ago, jaylw314 said:

Ask him if he has the gear to bench test the mag.  Either that, or reinstall the mag, disconnect the ignition harness at every spark plug, and hold each spark plug wire near a chassis ground to see how far you can get it to spark while cranking (CAREFULLY, of course).  That will tell you how strong the left mag is, assuming that is the mag in question.  It won't tell you anything about the right mag, though, since it has no impulse coupling.

Oooh, I just realized this applies to the IO-360 A3B6 with the two Slick mags, but I forget which mags have impulse couplings in the A3B6D dual mags...  Bench testing should work the same with either, though, they can spin the mags fast enough on the bench.

It is safer, and easier to take out all the top spark plugs then screw them back onto the leads and lay them back on top of the cylinders. Then just flip the prop and watch the plugs for spark. You won’t get shocked and there won’t be any compression so it will spin easier and no chance of the engine fireing.

To do the bottom ones, just move the plugs to the bottom leads.

Edited by N201MKTurbo
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18 minutes ago, N201MKTurbo said:

It is safer, and easier to take out all the top spark plugs then screw them back onto the leads and lay them back on top of the cylinders. Then just flip the prop and watch the plugs for spark. You won’t get shocked and there won’t be any compression so it will spin easier and no chance of the engine fireing.

To do the bottom ones, just move the plugs to the bottom leads.

You're right, I like that idea better! For @WaynePierce, you'd want to make sure you had new copper spark plug gaskets on hand.

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5 hours ago, Oldguy said:

Wayne, when you download from the EDM, the two options are "All" or "New". If you select "New", it downloads everything since the last time you downloaded, so you should have captured the initial run as well as the restart. While it may be two files, you should be able to look at them and see something happening at the end of the first file. If you uploaded everything to Savvy, you should see multiple flights recorded for the day in question.

I think I selected New. I've got everything that was on the jump drive loaded here... https://savvyanalysis.com/my-flights/1005889/6b82a73f-86bb-4264-b96a-63296fd717bd

I still think I've got a couple of issues. I must not have saved the 2 second interval because it looks like it's still set at 5. I don't think it recorded both the start and re-start. It looks like I've only got most of the original start and not the re-start.

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3 hours ago, N201MKTurbo said:

It is safer, and easier to take out all the top spark plugs then screw them back onto the leads and lay them back on top of the cylinders. Then just flip the prop and watch the plugs for spark. You won’t get shocked and there won’t be any compression so it will spin easier and no chance of the engine fireing.

To do the bottom ones, just move the plugs to the bottom leads.

I sent him a text today and he said he was going to test them/it today. I've not heard anything back. Before we removed the Mag he checked all the wires for unusual marks, he checked the mag cover for signs of arcing and didn't find anything out of the ordinary, he checked the points and they looked good as well. He said he had things back at the shop to test the capacitors and the coils. I'm not sure if he has a bench tester or not.

With all that being said, I was amazed at how familiar a Mag looks. I used to be able to swing a wrench on cars back in the 70's, when you could actually work on a car without a computer hooked to it, and that mysterious Mag that I've always heard about just looks like a distributor! In this case it was two Volkswagen distributors trapped in one but it was definitely something that I knew what I was looking at. 

 

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30 minutes ago, WaynePierce said:

I sent him a text today and he said he was going to test them/it today. I've not heard anything back. Before we removed the Mag he checked all the wires for unusual marks, he checked the mag cover for signs of arcing and didn't find anything out of the ordinary, he checked the points and they looked good as well. He said he had things back at the shop to test the capacitors and the coils. I'm not sure if he has a bench tester or not.

With all that being said, I was amazed at how familiar a Mag looks. I used to be able to swing a wrench on cars back in the 70's, when you could actually work on a car without a computer hooked to it, and that mysterious Mag that I've always heard about just looks like a distributor! In this case it was two Volkswagen distributors trapped in one but it was definitely something that I knew what I was looking at. 

 

Well, AFAIK, a mag is pretty much a distributor with the coil built-in instead of separate.  Not that I've ever seen a distributor, that was way before my time :P

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Mag...

distributor + coil + alternator...

Fully independent of the electrical system...

They were real modern technology back in the day...

Changing ignition timing is slightly more involved than rotating the distributor cap...

 

Best regards,

-a-

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I had the same thing happen.  The problem started as mag check, and no drop in RPM at all.  Found a broken ground (P wire?).  The fix, put a new terminal end on the P-wire and reattach.  Surprise, mag check, 1st detent, normal, 2nd detent, engine dies.  Problem was the mechanic trapped some of the wire insulation in the new terminal with the hot wire, so it grounded out the mag, and when running only on that mag, the engine died.

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On 11/4/2018 at 3:03 PM, teejayevans said:


Savvyanalysis.com allows you to upload, from which you share.

I just did my first SavvyAnalysis upload (EDM-830). Love it!

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20 hours ago, byrdflyr said:

  Surprise, mag check, 1st detent, normal, 2nd detent, engine dies.  Problem was the mechanic trapped some of the wire insulation in the new terminal with the hot wire, so it grounded out the mag, and when running only on that mag, the engine died.

Did this persist or was it intermittent? Some times it would die but some times it ran fine?

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