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Rising CHT's and Falling EGT's

The Wizzard

Well Known Member
I have one P-Mag and one Slick Mag. During a flight I had last week in about a 2 min. period the Cht's rose about 50-60 degrees (all 4 cylinders) and the EGT's dropped about 150 degrees at the same time in about a 2 min. period. I noticed the sound of the engine had changed and that's what first caught my attention. At that point there was an airport within 10 miles of my location and I landed the airplane to troubleshoot the problem. Nothing abnormal was found. There was also a 30 degree rise in oil temperature after the 2 min. period. No, I did not check the mags in flight however they did check OK on the ground.

Aerosport Power IO-375-M1B 6500' MSL

Could the P-Mag have advanced it's timing somehow? Any suggestions are welcome. I have spoke with the folks at E-Mag and they say without the problem occurring again inflight and checking the mags when it does there is no way to tell. I have flown 10 hours since and have not had the problem re-surface.
 
While the timing could have gone off than back, I suggest that is unlikely. I would however verify the pMag jumper wires in place and secured. If loose than your timing could have jump up 5 degrees (depending on MP and RPM). I'd also make sure your mag did not skip a few gear teeth and jump timing.

If you were running ROP at the time then I'd also look at a fuel starvation issue, as in throttle open but less fuel going to the engine. This would explain the CHT increase but as you had EGTs drop (opposite of expected) you have conflicting indications. If you had a corresponding drop in power (perhaps causing the change in engine sound as the prop should go flat), then the leaner mixture would push CHTs higher but the overall drop in power would perhaps lower EGTs as well. Need more data.

The prop going flat would also increase your oil temps and CHTs as it becomes a big, flat disc cutting off engine cooling.

What else can you tell us? Do you have an EMS that takes data? Where your ROP and if so how much? What RPM and MP? If you have EMS data what happened to fuel flow during this incident?

Carl
 
No Carl.......bad advice.

If he was ROP, and a fuel starvation the EGT would have risen also.


THIS IS WITHOUT DOUBT a timing error and I would suggest a lot more than the jumper wire difference. Maybe that is all it was, but I very much doubt it.

This is very much preignition and if you see it again, kill a mag and watch the EGT/CHT, you want to kill the mag that caused it immediately.

Immediate course of action is remove and destroy (Yes destroy) every spark plug in that engine before further flight. No ifs buts or anything. Remove and destroy. They have been subject to some potential damage to the ceramics. They are cheap.

Next while the plugs are out, have a good look with a borescope. Just to be sure.

These engines are very tough, and you probably had a low dose of preignition, but I have seen many engines trashed in not much more than 2 minutes. Usually on one cylinder only and usually from a failed ceramic on a spark plug.

I would love to see the data file.
 
During a flight I had last week in about a 2 min. period the Cht's rose about 50-60 degrees (all 4 cylinders) and the EGT's dropped about 150 degrees at the same time in about a 2 min. period.

Aerosport Power IO-375-M1B 6500' MSL

Symptoms do suggest abnormal combustion. "All cylinders" suggest timing. David's suggestion to inspect with a borescope is a good plan.

Assuming a detonation event, cut the oil filter, pull out the element, wash carefully in a white dish. If you see a lot of very dark, non-magnetic fines, it's probably lead, blown off the combustion chamber and piston top.

Could the P-Mag have advanced it's timing somehow?

First things first. Cut the filter, check the cylinders. Relatively clean, bare aluminum areas, possibly with a sandblasted look, are typical of detonation. The usual deposits may have edges which look melted, maybe even shiny. You may see little tiny balls, about the size of sand grains.

Ten hours of flight since the event will complicate diagnosis.

IF you find clear evidence of detonation, then consider cause. Pop the top off the Slick and make sure everything looks normal. If it's all good in there, the p-mag is next on the list, but like the factory crew, I don't know a good telltale. "Can't fix it if it won't stay broke" is a classic issue with electronic controls.
 
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More information

Gentlemen, Thanks for the input! Here is more information. I am running a whirlwind RV-200 constant speed prop. The Manafold Pressure and RPM as well as FF were all constant at the time. I was running the engine at slightly lean of peak about 7.8 GPH. Yes, I did have the data logged and uploaded it to Saavy and Cirrus reports. I did erase the SD card after after all of my flights were uploaded to both web sites. Dumb! Does anybody know how to download the data that has been uploaded to them? I tried to do that last night on Savvy's website but all it lets you do is share it.

I did an oil change after returning from the trip and I do have the oil filter on the workbench. I will cut it open when I return home. (Im an airline pilot and yes Im working!)

Im going to share with you my user name and password for Savvy. [email protected] Pass=Shunknife#45 N524DC

It's the flight from Hamilton NY (VGC) to Olean (OLE)

One other thing I want to pass along, I have messed with car engines since I was a kid. Im sure everyone has set the timing on a distributor before so you know what the engine sounds like when it's either too far advanced or too retarded. Looking back on this flight I was paying particular attention to everything the entire flight because "something" did not sound right and you will notice a slight jump in the CHT's earlier as well. Another note, I removed the jumper wire and installed an Enginebridge PMAG controller(https://www.enginebridge.com/product/eiwifi/) about a year ago. No, I do not have it displaying on my G3X and no I did not have my iPhone connected to it at the time.

I did wi-fi it to my cell phone and the subsequent flight home to monitor the advance of the PMAG and saw nothing abnormal on that flight.

I flew the airplane last week after the oil change with the enginebridge connected to my cell phone and noticed a few things.

On the ground:

800 RPM 9.3MP 25.2 degrees advance
1200RPM 8.6MP 28.0 advance
1600RPM 11.1MP 29.4 advance
1800RPM 12.7MP 30.8 advance
2300RPM 16.4MP 35.0 advance

Note: The ignition is at 25.2 degrees BTDC at idle, I thought it should be at 20 BTDC until 1800 RPM.



In the air

4500' 2500RPM 23.3MP 35 advance
2500RPM 24.0MP 32.2 advance
2500RPM 24.5MP 30.8 advance

Notice the drop in the advance as I increase MP

Same thing at 5500' MSL

2500RPM 24.8MP 28 advance
2500RPM 23.0MP 35 advance
2500RPM 22.6MP 35 advance

The first phone call I made was to Airflow performance and spoke with Kyle about what may be going on and his first question to me was "do you have an electronic ignition"? The second phone call I made was to E-Mag and spoke with Brad. He told me that he had not heard of such a thing and that in "no way could the PMAG advance to a value greater than 41degrees". As a side note I have tried to contact him over the past two weeks and none of my phone calls have been returned. The third phone call I made was to enginebridge asking them if the unit I have connected to the PMAG could have changed the settings somehow in the PAG and his answer was NO. Like I stated earlier, my cell phone was not wi-fi connected to the enginebridge at the time of the occurrence.

Well, There is a lot stuff to chew on here! It's my understanding from a previous conversation with EMAG that up to 1800 RPM the PMAG ignition should be at 20 degrees BTDC. After 1800 RPM then it looks at MP. It should stop at 35 degrees BTDC which it appears to be doing but can go to 39 degrees. EMAG limits it to 41degrees. Note, timing is in 1.4 degree increments in other words timing may be 25.4 degrees.

The EMAG firmware was update to the current version (41 I believe) in January of 2020 and the slick magneto was overhauled at the same time, both during condition inspection.

Dave
 

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Gentlemen, Thanks for the input! Here is more information. I am running a whirlwind RV-200 constant speed prop. The Manafold Pressure and RPM as well as FF were all constant at the time. I was running the engine at slightly lean of peak about 7.8 GPH. Yes, I did have the data logged and uploaded it to Saavy and Cirrus reports. I did erase the SD card after after all of my flights were uploaded to both web sites. Dumb! Does anybody know how to download the data that has been uploaded to them? I tried to do that last night on Savvy's website but all it lets you do is share it.

I did an oil change after returning from the trip and I do have the oil filter on the workbench. I will cut it open when I return home. (Im an airline pilot and yes Im working!)

Im going to share with you my user name and password for Savvy. [email protected] Pass=Shunknife#45 N524DC

Dave

This doesn't look to be timing related and doen't match the description in your first post. If your timing advanced 5 degrees, I would expect a rapid decrease in EGT (a few seconds), followed by a slow increase in CHT (couple of minutes). Your attached chart shows the opposite: a moderate rise in CHT (along with small rise in EGT), followed by a drop in EGT after the CHT peaked and began it's decline.

Can't say for sure what caused this, but it doesn't not look anything like the results that I have observed from experimentation with advance.

Larry
 
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Oil filter opened and plugs changed

Okay guys, who's next? Filter opened and inspected, nothing in it!

Plugs replaced

Boroscoped cylinders and all looks good
 
Pull the pMag controller box as that is a huge unknown. Install the jumper on the pMag. Verify timing set on both the mag and the pMag (assuming your engine base timing is the mag at 25 degrees BTDC, then set the pMag at TDC.

Did you just do the mag 500 hour check? If so it is also on the suspect list.

Test. Include an inflight mag check.

Carl
 
Okay guys, who's next? Filter opened and inspected, nothing in it!

Plugs replaced

Boroscoped cylinders and all looks good

You haven't provided enough data to troubleshoot this. I gave you reasons why I don't believe it is simply ignition advanced a bit too far, but there is not enough additional data here.

Assuming I am reading the chart scales correctly, it appears that your CHT's rose 100*, from normal operating temp, in 2-3 minutes. If that is the case, moderate to severe detonation is the most likely culprit and the most likely cause of detonation in your case is timing too far advanced for the power level and/or mixture. Again, not enough data here for anything beyond pure speculation.

Larry
 
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