Hot EGT, help diagnose

[Shadrach]

How will a mag check tell him if his MX inadvertantly or sloppily set the timming too far in advance the last time the plane was apart?  Failed plugs or failed mags do not cause typically cause an increase in CHT...only an increase in EGT. 

[kmyfm20s]

How will a mag check tell him if his MX inadvertantly or sloppily set the timming too far in advance the last time the plane was apart?  Failed plugs or failed mags do not cause typically cause an increase in CHT...only an increase in EGT.

The differential rise in EGT between the mags will help determine if timing is equal in normalized mode. The EGT rise should be equal or close to it between the left and right. It just help in the process of elimination.

[201er]

BTW ground mag checks have been good. Normalize shows rise in all EGTs and RPM difference between both mags is negligible.

[Marauder]

BTW ground mag checks have been good. Normalize shows rise in all EGTs and RPM difference between both mags is negligible.

Kind of feeling like you are visiting a doctor? Wait until you are old enough to have your prostrate checked. Then you will really know what the word "probed" means!

[carusoam]

On a side note...

Ross, where have you been, long time no see?

Or is it my memory challenges kicking in again?

Best regards,

-a-

[Shadrach]

On a side note...

Ross, where have you been, long time no see?

Or is it my memory challenges kicking in again?

Best regards,

-a-

No you're still as sharp as I remembered! Been away from here, not from the plane. This time 2 years ago I was a single man that had just punched out of corporate gig during a merger. I had a lots of time and energy to work on my career as resident Mooneyspace blowhard...

Then came a new gig with a small company and 60hr weeks. Met a wonderful girl; got married (eloped via Mooney)! No time to Mooneyspace. I got a nice PM from John P last week asking the same question you did. I stopped in for a bit and found it hard to leave. Good to see some new folkes as well as familiar ones. Thanks for asking!

[yvesg]

Kind of feeling like you are visiting a doctor? Wait until you are old enough to have your prostrate checked. Then you will really know what the word "probed" means!

... and when you get it checked, if you feel BOTH of his hands on your shoulders... run!

[Shadrach]

... and when you get it checked, if you feel BOTH of his hands on your shoulders... run!

Ewwwwwwww!

[201er]

I did an in flight mag check. At about 2500ft, 2700RPM, WOT, 11GPH, I ran it on the right mag, then the left mag. Ran a bit bumpier than both but nothing drastic. What was drastic however were the EGTs!

 

Running on the right mag EGTs went from around 1450 to 1550 EGTs. Then running on the left mag they rose considerably higher. 1600-1650 on the hottest EGTs. That #4 cylinder was always running the hottest EGT in all cases. Interestingly CHTs dropped off during single mag operation. Is that bad/strange for the EGTs to be substantially higher across the board on one mag than the other? What does that mean?

 

Also I have noticed that my #4 has been last to peak in all tests today. Is that the most logical reason for why it is running hottest CHT LOP? Should I try having the #4 injector swapped with one of my cooler cylinders?

[jetdriven]

Mike, I am seeing similar results as you are, the A3B6 must be a different animal than the B6D.  The #2 cylinder is far richer than the other three, it peaks about 0.6-0.8 GPH richer than the others.  Also, the #4 EGT value in cruise is ~50 degrees hotter than the others.  And we had a mag failure and flew for two hours over the panhandle of Florida in the dark. The EGTs were in the 1600 range in cruise, which was about 110 degrees hotter than normal. On final the #4 EGT was 1650 degrees.  I didnt want to do a mag check because I suspected a mag had failed. 

 

We put in GAMI injectors, and now have an "F" injector in #2, and a C-H-D injector in #1,3,and 4 respectively. The end result, #2 peaks 0.6-0.8 GPH before the rest, which are all in line.  "A" is the richest injector, "F" is the leanest, yet we still have this problem.

[Super Dave]

I would have your timing re-checked. Given the higher EGTs on the left mag, I suspect that your right mag is more advanced. Advanced timing could explain the hotter CHTs you've seen since your timing was adjusted.

[pinerunner]

Watch that video, it goes over just about everything. While you're getting quite a smorgasboard of information here, why not send it to Busch at the SavyAviator? I think the fee for a one time consult is like a couple of hundred. Then you could share the results with us. I do recall a warning not to get too hung up on EGT's and that there's no need for them to be balanced. What's going on in your exhaust is a pretty chaotic process, pulsing start  with each engine cycle, feed back from other parts of the manifold.

[201er]

I did watch the video. Very helpful and convinced me to do the mag check. Dave, what makes you think that? The mag with the hotter EGTs is excessively retarded?

[kmyfm20s]

I'm not a mechanic but I would suspect timing is slightly off and EGT's should be a closer spread across the board. I would also look at the individual spread of #4 to see if it greater. You may just need to clean the spark plugs, rotate then, or both.

[N201MKTurbo]

As I stated before the more retarded mag will give the higher EGT reading. The more retarded you are (well, your mag is) the less time there is for the fuel charge to burn. This will put less heat into the cylinder and leave more heat in the exhaust gas because burning is not complete. Thus your CHT goes down and your EGT goes up.

 

Considering that #4 did not go crazy on either mag, it doesn't look like an ignition problem. It is always good to have your mags synced, but that is not your problem.

 

I had an instructor from the Emily Griffiths School (A&P) tell me the rotational alignment of the fuel injector nozzle would have an effect on the mixture of the individual cylinders. I have found this to be correct. The letter stamped on one of the flats of the injector nozzle is opposite the vent hole. If you align them all to the same orientation to your cylinders you will get mort consistent mixture.

 

I do this by taking a 1/2 inch six point deep socket and wrapping it with 2 inch masking tape. I then put a vertical line along opposite flats of the socket so I can see how they are pointed while tightening. One line is aligned with letter the other is 180 degrees away. I put the vent holes towards the cylinder head.

 

The theory is that the air density changes with temperature and there is quite a difference in temperature with the vent hole pointed near the cylinder or away from the cylinder.

 

This effect is vary small, but so is the problem with your #4 cylinder.

[kmyfm20s]

Just to get this retard straight is 20 or 25 degrees more retarded:) How much of a temp spread between the left and right mag would indicate a timing issue?

[N201MKTurbo]

20 is more retarded. The number is the number of degrees of crankshaft rotation before TDC that the spark fires. More advanced is a bigger number and will fire sooner thus giving the fuel charge more time to burn in your cylinder. It affects the rotational position of peak cylinder pressure, which should ideally be at 15 degrees after TDC.

 

Ideally we could control the spark advance in the cockpit. But the danger of detonation is too great so they don't let us....

[jetdriven]

I also mark the flat on the injector opposite the letter, to index them properly. Sometimes its difficult to align them properly and also get the torque right. Definitely use anti-sieze on them.

[N201MKTurbo]

From everything that I've seen your plane is fine. Go watch some football and drink some beers and quit worrying about your plane.

[kmyfm20s]

Are non mechanics allowed to mess with the injectors, clean, rotate ect?

[jetdriven]

Yes, but only under supervision of a rated powerplant mechanic.

[N201MKTurbo]

The reality is that if it is your plane you can do anything you want with it. If you know what you are doing, no problem. If you do something wrong and have an accident, there will be hell to pay.

[Super Dave]

I did watch the video. Very helpful and convinced me to do the mag check. Dave, what makes you think that? The mag with the hotter EGTs is excessively retarded?

Absolute EGT values are meaningless, as is cylinder to cylinder EGT variation. But when all EGTs increase more on one mag than they do on the other, it is a text book symptom of a timing variation between the mags. M201MKTurbo makes a good explanation of why.

I'm not saying that the mag with the higher EGTs is excessively retarded, I'm just suspecting (with pretty good certainty) that it is retarded farther than your other mag. Maybe the hotter EGT mag is timed correctly and the other one is excessively advanced?

Somewhere you said that the high CHT started happening right after you had your timing reset to 25BTDC. Advanced timing will increase CHT. Not that 25BTDC is necessarily to far advanced, but if timing was previously at 23 or 20, the change could explain the now higher CHT.

Advanced timing has some advantage in efficiency and horsepower, but if I were not able to run cool and smooth LOP at 25BTDC, I would consider going back to 20BTDC.

[kmyfm20s]

As I stated before the more retarded mag will give the higher EGT reading. The more retarded you are (well, your mag is) the less time there is for the fuel charge to burn. This will put less heat into the cylinder and leave more heat in the exhaust gas because burning is not complete. Thus your CHT goes down and your EGT goes up.

 

Considering that #4 did not go crazy on either mag, it doesn't look like an ignition problem. It is always good to have your mags synced, but that is not your problem.

 

I had an instructor from the Emily Griffiths School (A&P) tell me the rotational alignment of the fuel injector nozzle would have an effect on the mixture of the individual cylinders. I have found this to be correct. The letter stamped on one of the flats of the injector nozzle is opposite the vent hole. If you align them all to the same orientation to your cylinders you will get mort consistent mixture.

 

I do this by taking a 1/2 inch six point deep socket and wrapping it with 2 inch masking tape. I then put a vertical line along opposite flats of the socket so I can see how they are pointed while tightening. One line is aligned with letter the other is 180 degrees away. I put the vent holes towards the cylinder head.

 

The theory is that the air density changes with temperature and there is quite a difference in temperature with the vent hole pointed near the cylinder or away from the cylinder.

 

This effect is vary small, but so is the problem with your #4 cylinder.

I looked at my injectors and they are in all different directions. So if I understand you correctly, if I have my top cowell off I should be able to read the letter on my injector and the letter should be facing the centerline of the engine?

[201er]

I should mention an update. I had the timing redone and sure enough it wasn't 25. Not sure how much the differential was. I also had the plugs rotated, injectors cleaned, and swapped based on my observations. Now it runs beautifully, all EGTs are +/-10 of each other in LOP cruise, smooth, cool, excellent.

 

Still hotter on right mag then left on an in flight EGT check but nowhere near as much as before. Thanks for the suggestions.