Huge drop in Mag check

[BravoWhiskey]

I did a run up so I can do a short flight to a maintenance shop to troubleshoot my electrical gremlin that is causing a draw on me when i use taxi and landing lights.  During the run up I had a severe mag drop of about 400rpm... for both.

Cleaned plugs and checked for water in fule, all good but still the same drop.  Mags are both fine... 

I'm at a loss... any thoughts experience or troubleshooting tips?  I Could use the 2005 M20M GX AMM for Garmin if anyone has a digital copy they could share...

[LANCECASPER]

6 minutes ago, BravoWhiskey said:

I did a run up so I can do a short flight to a maintenance shop to troubleshoot my electrical gremlin that is causing a draw on me when i use taxi and landing lights.  During the run up I had a severe mag drop of about 400rpm... for both.

Cleaned plugs and checked for water in fule, all good but still the same drop.  Mags are both fine... 

I'm at a loss... any thoughts experience or troubleshooting tips?  I Could use the 2005 M20M GX AMM for Garmin if anyone has a digital copy they could share...

How do you know your mags are both fine? When and where were they last overhauled or at least inspected?

[MB65E]

I have yet to see a set of slick mags make it past 500FH with out issue.How many hours on the mags. 

-Matt

[BravoWhiskey]

Overhauled with motor... 12 hrs ago.

[MB65E]

I’ve had them fail out of the box too.

-Matt

[BravoWhiskey]

Just now, MB65E said:

I’ve had them fail out of the box too.

-Matt

Both drop at the same time is what gets me.   Meaning i didnt have one normal and one fail a few weeks ago.. this happened to both on Tuesday.

[AIREMATT]

Maybe more of an electrical issue than just your lights.

[FoxMike]

You might check the engine timing.

[BravoWhiskey]

19 minutes ago, AIREMATT said:

Maybe more of an electrical issue than just your lights.

oh no doubt.  

[larryb]

I once had an excessive mag drop on both mags when my idle mixture was way too rich. Pulling out the mixture a bit allowed for a decent mag check. But the real problem was in my just-overhauled fuel pump had a flaw in the overhaul and had to be sent back.

 

Larry

[Shadrach]

Skeptical that this is a mag problem given that two independent ignition sources manifest the same symptoms. Could be a mixture issue. Could also be ignition related downstream or upstream of the mags.

Edited December 9, 2021 by Shadrach

[EricJ]

Lean it to peak rpm or a little less at runup rpm and try it again.   If it persists, check timing, plugs, etc.

 

[LANCECASPER]

2 hours ago, BravoWhiskey said:

Overhauled with motor... 12 hrs ago.

Was this a field overhaul with the mags sent out to an independent shop? Or a factory reman, in which case they would have been new mag? 

[BravoWhiskey]

Independent shop.  

[ArtVandelay]

Was this a field overhaul with the mags sent out to an independent shop? Or a factory reman, in which case they would have been new mag? 

Some field overhauls install new mags, mine did, check your log entry.

[LANCECASPER]

New slick mags have had a history of being bad out of the box. It seems like that might have improved. 

Some shops that specialize in these are great at keeping these going, other shops don’t have the best track record. 

[BravoWhiskey]

New plugs... of all things i didnt expect that to be the problem.  Ran smooth, 110 rpm drop on both sides.  

[LANCECASPER]

7 hours ago, BravoWhiskey said:

New plugs... of all things i didnt expect that to be the problem.  Ran smooth, 110 rpm drop on both sides.  

Let me guess - the old ones were Champions?

[BravoWhiskey]

They were fine wire but not sure of make... replaced with massive.