Mage Problems

by Johann VB in General Tech Discussion 9 years ago

Good Day
I when for a flight this morning and all was 100%. After a 1.4 hr flight I returned to refuel. The refueling was +/- 30 min. I thought the weather is so nice I would like to go for another hour or two. Ambient +/- 26ºC with a density alt of +/-6880ft

At the holding point I did the Mage check and picked up a problem. Idol up @ 4000rpm Mage A – OFF, RPM drop > 500? Mage A - ON motor return to 4000RPM no problem. Mage B – OFF RPM drop +/- 50 rpm Mage B – ON motor return back to 4000 rpm no problem. The motor had a 200hr service 5 hours ago. I then returned back to the hanger and replaced all the plugs. With the same problem? Can you please advice as to what I can look for? All wiring is 100%. When I did the Mage check in the morning all was 100% Mage A Drop +/-50 – 100 rpm Mage B drop +/-50 - 70rpm

Re: Mage Problems

by Johann VB » 9 years ago

Johann VB

2 2 0

Sorry it is a 912 ULS

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Re: Mage Problems

by Rob Seaton » 9 years ago

Rob Seaton

3 1.32k 251

Divide and conquer:
1: Eliminate the switches from the problem. Remove the P-leads (also called grounding wires and ignition wires) and install temporary test leads so you can ground the wires to the engine block. Run engine and touch each wire, one at a time, to the engine block see if mag drop is the same. You need a brave, competent, trained person to do this work as you are working with a running engine, exposed wires and high voltage!!
IF the mag drop is OK then you have a problem with the switch or wire or the switch ground.
IF not OK leave the p-leads disconnected for the next tests:

2: De-pin and swap the red stator wires. If the problem goes to the other side you have a stator problem: ohm out each red wire to its ground ring terminal, maybe you just have a bad ground or broken strands in the wire. (Access red wire grounds through flywheel holes before removing stator. Ohm out each red wire separately with the ground ring terminal disconnected to get a true reading.

3: Swap the trigger coil wires (remember if you have six-pin connectors you are also swapping the p-leads so leave them disconnected and use the temporary test leads)
Problem goes to other side? You have a trigger coil problem. Ohm out each trigger pin to solder joint.

4: Swap module/coil connectors. If problem moves to other side you have a faulty module.

5-Coils: (Very unlikely to be the problem) ohm out primary and secondary wires. At the same time, clip off 5mm of the secondary wire to get a good connection to the spiral prong in the spark plug cap. Clean the primary ground wires (at the 1/3 intake manifold)

6 -In the end carb problems are much more likely to be the cause of a bad mag drop. But a 400+rpm drop is also likely to be an ignition problem.

Why does a carb problem show up as a high mag drop on one ignition? Because each ignition fires 4 top plugs and 4 bottom plugs and the bottom plugs are "less optimal" (they are not positioned in the combustion chamber as well as the top plugs and they tend to get more fouling). Combine this with 2 separate carbs and you can have confusing diagnostics. Also the induction system is not perfect; the fuel/air mixture has a longer/straighter path to the #1 and #2 combustion chambers so you get rich/black plugs in the front cylinders at idle and low rpm. At higher rpm they work fine so if your mag drop is fine at high rpm and bad at low rpm then consider the carbs to the problem.

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Re: Mage Problems

by Johann VB » 9 years ago

Johann VB

2 2 0

Thank you Rob I will follow your advise

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Mage Problems

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