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Mag drop

  • bnelson79
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1 month 1 week ago #22857 by bnelson79
Mag drop was created by bnelson79
I have a 912 UL engine on a ppc, with only 125 hours on it. Recently completed annual condition inspection, replaced plugs, and all seemed fine. Today started, warmed to 122, and found that running at 3500 rpm the mag drop was only 10 or 20 on one side, but 500 on the other, with engine running mildly rough. Obviously something is wrong with one or both mags. Any suggestions about where to start, or what most likely problem might be would be appreciated.

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1 month 1 week ago #22858 by garrett
Replied by garrett on topic Mag drop
Make sure you did not get heat transfer compound on the electrodes of one or more of the plugs, all plug caps are pushed on all the way to the plug, including the wires in in the coil packs. Also try trimming 3/8" off each end of plug wire at coil pack and plug cap reinstall with dielectric grease. Verify ignition ground on the ignition modules and coil packs.

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1 month 1 week ago #22859 by bnelson79
Replied by bnelson79 on topic Mag drop
Checked plugs. They all looked good. Switched bottom to top. Restarted and found everything the same. Same mag dropping 500-600, other still 10-30.

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1 month 1 week ago #22861 by garrett
Replied by garrett on topic Mag drop
You can swap the ignition modules and the take a meter and verify the grounds, check for broken wire under insulation near connectors. Verify the resistance from plug cap to plug cap I forget what the value is but if you notice one plug cap goes to the plug wire then to the coil and back out of the coil to another wire and plug cap. The total resistance of all 4 of each of these circuits should match. Or just individually measure the resistance of the parts and look for a discrepancy by comparing.

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1 month 1 week ago #22863 by MesquiteTim
Replied by MesquiteTim on topic Mag drop
"checked plugs" means what? They all appear to be firing? I would put old plugs back in the bad mag side. One of your new plugs is probably bad.

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1 month 1 week ago #22865 by bnelson79
Replied by bnelson79 on topic Mag drop
Reversed mag check p-leads on test switch. 500 rpm circuit drop reversed as well. Checked resistance from cap, across coil and wires to opposite cap. All 4 circuits measured same resistance, so coils, spark plug wires, and caps should be good. Now, maybe a very expensive module to replace, or first replace inexpensive plugs. Will try that tomorrow. If that doesn't work will call Lockwood onMonday. Does anyone have any other ideas?

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1 month 1 week ago #22866 by garrett
Replied by garrett on topic Mag drop
I also took Roger Lee's advice in regards to plug gap and set at .023" the engine seemed to run better with the gap at minimum setting.
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1 month 6 days ago #22870 by bnelson79
Replied by bnelson79 on topic Mag drop
Replaced spark plugs. Still doing the same thing. Will call Lockwood. Sounds like trouble woth on of the modules. Any other suggestions or thoughts?

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1 month 2 days ago #22909 by bravo23c
Replied by bravo23c on topic Mag drop
Some have had dirty, corroded grounds from the modules to the engine causing some weird mag drops.
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1 month 2 days ago #22910 by bnelson79
Replied by bnelson79 on topic Mag drop
Thanks. Not that old or that many hours. Connections are shiny and clean. Think the problem is a bad module.

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