EGT slope question

I have been noticing that EGT 3 behaves differently than the other EGTs. I am not talking about the specific temperature compared to the other EGTs but more the trend of EGT 3. Does anyone have an idea of what can be going on? Thanks for any advice you can provide.

On the first picture you can see EGT 3 drop at about 37 seconds when all the other EGTs where climbing. Then it started climbing again and eventually stabilized with the same slope as all the other EGTs.


On the second picture you can see the EGT 3 slope behaved differently than the others. This sequence was recorded when I reduced power to land. Interesting are the points at 43:22, 44:15, 45:20. At those times the slope changes from decreasing to increasing while all the other EGT slopes remain the same.

The probe has 30 hrs since new. I did a calibration test on all the probes and oat sensors. The difference between all 10 sensor from highest and lowest were 2 deg f. I doubt that is the problem but i can check them again.

It kinda seems like the difference widens with lower manifold pressures. I am assuming FP prop, but it up to 1800 rpm it won't make a difference.

So - acting like an intake leak? I suppose it could be bad distribution but if it is really tracking man "vacuum" then would look to intake leak.

Just a first look.

Ah yes, the Long Distance Hail Mary Diagnosis

Pull the nozzle restrictor and remove the little bit of aluminum trash.

Rationale: in the first photo #3 is lean, then stops firing for a moment (note tach drop), then continues leaner than the others until RPM (and injector line pressure) is raised. Note than a partially stopped restrictor makes the other cylinders go a bit richer, pushing their EGTs down.

Agreed!

DanH said:

Ah yes, the Long Distance Hail Mary Diagnosis

Pull the nozzle restrictor and remove the little bit of aluminum trash.

Rationale: in the first photo #3 is lean, then stops firing for a moment (note tach drop), then continues leaner than the others until RPM (and injector line pressure) is raised. Note than a partially stopped restrictor makes the other cylinders go a bit richer, pushing their EGTs down.

Click to expand...

It is possibly a piece of the SS wire braided cover on a fuel line. Had this happen -- I'll bet that if a I had a clue how to download the data, it would have shown the same thing.

It's a 10 minute fix - piece o cake!

Carry on!
Mark

1 plug fouled

You may have one plug not firing at the time when the EGT rises above the rest. With one plug firing the combustion is not as complete as the other cylinders and is still going on when the exhaust valve opens. This is why you get an EGT rise while you do a mag check.

DanH said:

Ah yes, the Long Distance Hail Mary Diagnosis
Pull the nozzle restrictor and remove the little bit of aluminum trash.

Click to expand...

Dan, I know it is difficult to diagnose via long distance but I can tell you that what you said made sense. So much so that I started to go through all my data with a fine tooth comb. I found other instances where the same thing is/was happening. The reason it was masked while I reviewed it was that the data was being displayed for the entire flight. I did not find that type of occurrence until I started braking down the flights in 5 minute increments. That allowed a finer resolution on the data collected.

The weird thing is that I have done the ignition stress test, the Gami test and all kinds of test and all have "passed". Will give it a look. Thank you!!!!!