RPM drop left mag and fouled plugs

[JoshMan]

Hi, Guys. 
Question for you all.  I have a 1969 M20E that I actually just picked up from annual one week ago.  Flew home OK no problem.  I flew to Peoria which is about an hour away to have some avionics work done on Saturday morning and I went to start the plane to return home and had a 250 RPM drop on the left mag.  It would not clear.  Also the EGT on cylinder 4 sky rocketed

We checked spark plugs and definitely the bottom plugs on cylinders 1 and 3 had lead deposits. He cleaned and test fired them and all were fine.   Mechanic is pretty sure he rotated the bottom plugs to the top on the same side but wasn't 100% confident today after talking to him.

Went to fly today and again 250 RPM drop on L mag, but it was cylinder 2 EGT that increased the most today.

I would appreciate any of your thoughts. I am busy in the hospital for the next couple days and will have a mechanic come check it out likely Tuesday but that is the information I have for now.  Ryan at KPIA thinks either a bad plug or potentially the MAG but thinks its probably not the case considering it worked fine after we cleaned the plugs yesterday.  He also suggested a clogged fuel injector. The spark plugs were put in brand new about 120 hours ago.

 

Thanks

Josh

[neilpilot]

Maybe you need to clean the injectors?

[Yetti]

how many hours on the mags?  are you leaning aggressively during ground ops?

[Yetti]

Also idle between 1100 and 1200 unless taxiing

[JoshMan]

about 200 hours on the MAGs and yes to leaning aggressively.  Have flown this plane 200 hours in the last year without this issue and has happened twice now in 2 days.  Picked it up from annual in Willmar last weekend.

[carusoam]

EGT skyrocketing is an indication that raw fuel is dumping into the exhaust instead of burning in the cylinder...

You might want to give numbers in this case. EGT on both mags is X. EGT on L mag is Y.  EGT on R mag is Z...

See why?

With a JPI...

You should be able to tell which plug is not working.

Without an engine monitor, you are only seeing one collective EGT or just a single EGT skyrocketing.

When doing a run-up you should be feeling some whacky vibrations as one cylinder is misbehaving.

Sounds like a bad plug moved from cylinder four to two... right from your description.

If you have Champion spark plugs, check the one with the highest resistance. It is sitting in cylinder two now...

Do a run-up on the ground look at the JPI to see what cylinder is misbehaving.  If the plug is dead it will really stand out.  If it is sort of dying, it still should show, but not night and day.

PP thoughts only, but I've read this around here before...

Best regards,

-a-

[Yetti]

Check plug wires to make sure they all got back to the correct home.  Or some wire ends may have got damaged.....  assuming plugs are good

[JoshMan]

Thanks, guys.  Will update you as soon as I know more

[Andy95W]

Sounds suspiciously like you had a bad spark plug on #4 that your mechanic moved to #2.  

Some spark plugs will test good but start to break down under heat and pressure.  Nearly everyone will suggest Tempest fine wire plugs, or the Tempest UREM 37BY long nose plugs to save a little money.

[AZM20C]

M20C

I had a similar problem last week. On runup one of the mags dropped about 250 rpm. The mechanic said the spark plug on the bottom #1 cylinder was bridged. We talked about it being lead. He said the obstruction fell right out when he put the spark plug on his work bench. He said lead was harder to clean out.

So, this is just  another variable for you to consider. 

[JoshMan]

Replaced the champion spark plugs with Tempest UREM37BY.  Run-up today was OK.  Mechanic also mentioned that leads looked pretty bad and suggested that they may not be carrying enough spark to burn optimally resulting in fouling of the plug.  Has this ever happened to anyone before? Either way new leads have been ordered.

[carusoam]

Old leads can get pretty ugly.

They are so low cost, by the time you have tested them it is probably better to replace them.

Many issues show up by taking them off every year for a decade...

Check how old they are in your logs...

If they aren't a pretty bright silicone color, they may be from the last ice age...

Best regards,

-a-