Learned something today/Engine Monitor/mag check

[scottfromiowa]

I was just checking "Pelican Brief" a lot of really good articles on AV Web regarding engine operation etc. and learned something new.  When doing run up for mag check a better/additional way to ensure mags and plugs are all functioning is to look at your engine monitor.  When you switch to single mag their should be an increase for each cylinder.  If one has a decrease likely means a plug is fouled or NOT functioning properly...

I am going to start checking my engine monitor for future flights.  Just wondered how many do this, or if it was "news" to anyone else.

[AustinChurch]

Sounds interesting.  When you say "increase", do you mean EGT's?

[Piloto]

More noticeable than the EGT decrease is the engine roughness. However the analyzer helps you identify the culprit so you know which plug to pull out.

José 

[N57039]

Been doing this for a number of years. Best way is with the engine leaned as much as you can and still get to 1800 rpm. The EGT's will rise nicely as each mag in turn is checked. Even better is to do this LOP in the air. Many of us do a LOP mag check in the air and don't bother on the ground. The check under load at higher altitude is a much tougher test of the mags performance.

[FlyingAggie]

Last week I stopped at Longmont to refuel and during run-up, the RPM dropped about 300 RPM on the left mag.  Checking the JPI showed the #6 cylinder going cold on the left mag while the other cylinders appeared normal.  So it made pretty easy to spot the fouled plug.  I was able to burn it off, but plan to pull it for inspection the next time I have the cowl off.  The JPI made diagnosising the problem easy.

 

[FlyingAggie]

Lance,

Isn't it a little late to find out that you have a mag problem after you have taken off?

Quote: N57039

 Many of us do a LOP mag check in the air and don't bother on the ground. The check under load at higher altitude is a much tougher test of the mags performance.

[DaV8or]

Quote: FlyingAggie

[Ned Gravel]

Quote: DaV8or

[Jeff_S]

Quote: DaV8or

[jlunseth]

I do three checks with the engine monitor.  One on each of the mags, and then the third with both mags on but leaning the mixture out.  It is suggested by JPI and you want to see the EGT's climb roughly equally on all of the cylinders.  I have seen recommendations to perform the mag check in the air prior to landing so you can get the mag repaired before the next flight if it is bad. 

[craigsteffen]

Quote: N57039

Many of us do a LOP mag check in the air and don't bother on the ground. The check under load at higher altitude is a much tougher test of the mags performance.

[Immelman]

A further tip, if your engine monitor has it, is to actiivate the EGT "normalize" view after setting runup RPM. On the JPI this is done by holding one of the buttons (the right, I think) for a couple of seconds. This causes all the EGTs to be displayed 'equally' and increases the resolution (i.e. small temperature change shows as a larger deviation in the bar graphs).

After that, select each mag -- now the EGT rises you're looking for on each cylinder are much more readily apparent, as are other things that are often too subtle to catch by ear, such as a plug thats "sort of" oil fouled and is firing *most* of the time.

 

[Jeff_S]

Quote: craigsteffen

Um...I hope I'm mis-understanding you.  Are you saying that you don't do a mag check during your pre-takeoff runup?  Do you ever fly IFR?  Do you fly with anyone else in the airplane that you care about? 

I don't dispute that checking the efficiency of the mags under load in the air is a far better diagnostic technique for spotting long-term problems.  However, I think that's a really bad idea for safety reasons.  You're risking taking off with one magneto totally dead.

 

[carusoam]

"It gives an LED warning if there is a problem with one of the mags" - Jeff S.

Jeff,

What kind of warning do you get?  Does the RPM gauge sense an output from each mag?

-a-

[66Super21]

Yes, when you install the Horizon tach you eliminate the mechanical cable and it senses each mag electrically.  It's a great item.

[Kwixdraw]

Quote: AustinChurch

Sounds interesting.  When you say "increase", do you mean EGT's?

[peter]

Quote: carusoam

Does the RPM gauge sense an output from each mag?

[Jeff_S]

Quote: carusoam

"It gives an LED warning if there is a problem with one of the mags" - Jeff S.

Jeff,

What kind of warning do you get?  Does the RPM gauge sense an output from each mag?

-a-

[ElectronicsInt]

Expanding a bit more on this topic.  Here is a handy cheat sheet of how various engine issues will indicate on multipoint EGT/CHT analyzers.  Handy to keep in the cockpit for me:)

Best regards,

[fantom]

To be fair, here is the JPI manual with graphics for engine issues as well.

http://njwg.cap.gov/Operations/aircraft_management_files/Manuals/PG_700-800%20Rev_R2.pdf