P-Mag problem - rough on both!??

Flew an hour this morning, found a problem that I can't explain.
After takeoff while climbing through 1400 feet, the engine abruptly became slightly rough. Grounding either P-Mag makes the roughness go away. (Grounding both P-Mags makes the engine very (too) quiet). The engine runs smooth on either P-Mag, but the roughness returns instantly when the second P-Mag is ungrounded again. This seems rather contralogical.

Engine is an ECI IO-360, 31 hours since new. OAT is 32F. The roughness is slight, not enough to make one immediately look for NRST, but clearly not as smooth as it was yesterday, discinctly noticeable. Fuel is 100LL. Injection is from Airflow Performance. The roughness is distinctly connected to the action of the p-lead switch.

Each P-Mag has a cooling blast tube. The manifold ports are tee'd together. Manifold pressure gage readings respond normally.

P-Mags are hardwired for the lower advance curve (A-curve??).

The roughness is less noticeable when leaned, but still distinct. The roughness is noticeable at all flight engine speeds. Below the constant prop control speed, grounding either P-Mag causes a 10-20 rpm drop, either P-Mag. Swithching off ships power to the P-Mags didn't appear to make any difference.

EGTs start rising when running on just a single P-Mag, and drop when returned to both.

Flew for an hour, the entire time the engine was exhibiting these symptoms.

Will put in new plugs and see if that makes any difference.

I am not making this up. I do not want a disease named after me. I want my smooth engine back! Any insight would be appreciated.

Thanks!

- Roger

From what you describe, I would start looking for wiring issues, something loose.

Didn't the pmags have a connector issue with the terminal screw hookups in the past------is this still what they use??

Has the engine always had the pmag, or have you just put them on recently??

The EGT sounds like the key here. You say it is rising on one, but rising to a more normal level? Or rising higher than normal?

Check your PM's.

new plugs, still rough...

Eight new plugs. Still rough on both, smooth on either P-Mag. Flew 36 minutes, notceable the whole time. Roughness is felt through heels on floor, through the windshield brace bar, through the seat.

Mike, the engine is new, has had these same two P-Mags for 32 hours now. Oil change 3 hours ago. Installed cylinder band heater 4 hours ago.

Scott, I think the EGT rise is normal for operation on a single magneto, as less of the fuel is burned in the cylinder due to single, slower flame front, and more heat is created in the header pipe. Correct me if I am wrong...

Not sure what other clues to discuss... The four into one, equal length exhaust is home made. Hangered. 32 hours in the past four weeks. Two oil changes. ???

Bill, I will call after dinnerl


Thanks for helping me think through this one.

Roger

P-Mags

I would check all wiring and MAP lines and make sure the units are securely attached to the engine. Re-time both units and test fly it. You may want to take note of the EGT while running both mags and then on each mag separately. A lowering of EGT's can indicate firing issues.

If you still have issues, call Brad at Emag. I'm sure he will have suggestions.

As a side note, the mags do have computers in them and there are precautions to take. I start with both mags on. I turn on the power to both mags then unground both mags. To shut down, once the prop has completely stopped, turn off the power to both mags, then ground them.

Very good post Jerry!

One other thing, make sure your MAP pressure is smoothed out before going to the P-mags. It is possible that a jumping MAP pressure could cause the P-mag's timing to jump around in flight.

Just a few points to help folk understand things that happen.

Scott, I think the EGT rise is normal for operation on a single magneto, as less of the fuel is burned in the cylinder due to single, slower flame front, and more heat is created in the header pipe. Correct me if I am wrong...

Click to expand...

This is not quite true. The fuel is generally all burned in the cylinder, unless the flame front is severely delayed, but what you are seeing when you switch one mag off is a delay in reaching peak pressure to a point further after TDC, and thus a greater volume in the chamber. The peak pressure is accordingly lower. Because you go from a higher pressure to ambient, compared to a slightly lower pressure to ambient the PV=NRT equation the Delta T is going to be greater. In other words if you expand a hot gas from a given pressure you have a certain temperature drop. If you do this from a higher pressure you get a greater drop.

Think about a BBQ gas bottle and what happens if you open the valve compared to doing it from a lower pressure. The higher the drop the lower the temp.

So when switching a mag off all EGT's should go up.

I agree with Jerry, retime the mags, and in my opinion knock off a couple of degrees while you are at it, by taking the prop past TDC a couple of degrees before you do the timing set point. I would also make sure there is some filtering of the MAP lines, usually a tiny orrifice or some dense filter media that will not move in the tube but dampens the pulses in the line. But not so much it under reads.

My biggest concern would be that you have mags firing off far too early. You can't hear pinging in a plane (although we believe one guy could many moons ago) but perhaps you can feel it. If you have any data files from your engine monitor send them to me at davidbrown ' at' advanced pilot.com and I will take a look.

And you might want to consider booking in for the class the boys over there teach in March. And nooooo? I don't make a buck out of it!

over-advanced timing...

RV10inOz said:

My biggest concern would be that you have mags firing off far too early. You can't hear pinging in a plane but perhaps you can feel it.

Click to expand...

David,

Thanks for the technical EGT explanation, I knew I was oversimplifying.

The postulation about firing too soon sounds plausible. It sounds/feels like that kind of a problem, not that I have ever heard/felt pre-ignition before. Running on a single mag would reduce the amount of pre-ignition, either mag. Exactly replicates the symptoms. Will check/ re-time this afternoon, not sure when I will fly again, WX moving in from Alaska.

Thanks for the thoughtful consideration of my problem.

- Roger

Since you describe this roughness as being a sudden change, I would check the A-B profile jumpers on both mags. My thought is that the ignition is too advanced in general but not far enough to get noticeable ping and a possible change in one mag via jumper failure is enough to cause the ping with both mags operating but the timing is not too far when operating single. Might be able to see a difference in EGT from left to right mag.

Roger, this may sound pedantic, and nit picky, but you do not have pre-ignition at all, if you did your engine would be completely trashed by now.

What you may be suffering is advanced ignition, or a jumping around ignition. Pinging is the slang word for detonation, and if severe enough, this can damage spark plug ceramics, causing a glow plug effect and inducing pre-ignition. The differences are huge!

I think Bill has detailed it very well. check this carefully.The other Bill, N941WR who makes the EI commander should probably sell you one of his devices so you can see what is going on. Otherwise get two mags

What concerns me is that the dual flame out that happened over here in an RV7 was close to disaster except the pilot was a retired Ag pilot and managed the emergency well. Many would not. He had similar issues and they both quit within 30 seconds of each other. I don't mean to scare you, but?..dont treat it lightly.

Do you have a data file to send me?

David,

Can you tell us more of the details or point us to a link about the RV7 and total flame out? IE what type/version mags (emags, Pmags, 113, 114, other) and the suspected cause etc.? I cannot understand how 2 Pmags would BOTH fail 30 seconds apart, other than a common gear within the accessory case. Even then, they would both fail pretty much at the same time.

Bevan

"What concerns me is that the dual flame out that happened over here in an RV7 was close to disaster except the pilot was a retired Ag pilot and managed the emergency well. Many would not. He had similar issues and they both quit within 30 seconds of each other. I don't mean to scare you, but?..dont treat it lightly."

OK David, you have my full attention

Please tell me more about how a dual flame out with Pmags could possibly happen and how to avoid such a thing.

I am receiving my engine tomorrow with Dual Pmags and have the EICommander in the panel.

What should I do to avoid the possibility of a dual flame out. I hate the sound of that...

Randall in Sedona
RV7A IO-375
WW RV200
Dual Pmags

Randy said:

"What concerns me is that the dual flame out that happened over here in an RV7 was close to disaster except the pilot was a retired Ag pilot and managed the emergency well. Many would not. He had similar issues and they both quit within 30 seconds of each other. I don't mean to scare you, but?..dont treat it lightly."

OK David, you have my full attention

Please tell me more about how a dual flame out with Pmags could possibly happen and how to avoid such a thing.

I am receiving my engine tomorrow with Dual Pmags and have the EICommander in the panel.

What should I do to avoid the possibility of a dual flame out. I hate the sound of that...

Randall in Sedona
RV7A IO-375
WW RV200
Dual Pmags

Click to expand...

If you are patient, I can get the story in detail, but I am heading off to Vanuatu for a week and will have to do this when I get back.

Basically one failed slowly over 30 seconds and then the pilot started to return to the field, shortly after the second one failed?..dead stick.

I think they went in the bin?.no research was conducted, which is kind of frustrating.

I have flown dual PMAG engined RV's and they work fine, but I am not convinced that there is any real benefit in having two. Even having one I do not like the excessive advance in some of them and I would fake it out a little, but you can't do that on all of them.

If you are going to have them have one. Use a Slick or Bendix on the other. The single biggest improvement despite what most people think, is they do operate smoother LOP. But thats it. Having two does not help this any further.

why does having two not give you the redundancy of two conventional mags?

sblack said:

why does having two not give you the redundancy of two conventional mags?

Click to expand...

It should, but why do you ask?

I think you have misread my post.