Further analysis from the new GI-275 data reveals that cylinder 3 appears to be too lean, which is especially visible during climb and results in elevated CHT. This is consistent over 7 flights. Curious if anyone has insight into what might cause this and what one would do about it.
Representative climb graphs:
Maybe you should state what engine you have. I guess the fixes are a bit different if it’s carbureted or injected.
150 degrees of EGT difference is quite a lot. I haven’t flown many carburetted aircraft with an all-cylinder engine monitor, but when I did, I did not notice quite such big differences. 1460 degrees sounds way too high for a full-power, full rich climb.
Anyway, I wouldn’t know what you could do about it, short of just setting up the whole engine richer.
What I don’t understand is: what is the “step” you see in EGTs just short of 00:12:00? Are you leaning shortly after takeoff?
What engine?
Carb’ed? When was the last OH of the carb?
If, I would check the gaskets in air flow tubes of the carb first.
Baffles check out?
What happens on shallower climb and more speed?
Sorry for the lack of detail. It’s an O-360 on a TB10.
boscomantico wrote:
What I don’t understand is: what is the “step” you see in EGTs just short of 00:12:00? Are you leaning shortly after takeoff?
This particular flight was a short climb, and yes the step is leaning.
MichaLSA wrote:
Carb’ed? When was the last OH of the carb?
What happens on shallower climb and more speed?
Last carb OH was 2016, 380 hours ago. On my next flight I’ll try a shallower climb and see what happens.
dutch_flyer wrote:
Sorry for the lack of detail. It’s an O-360 on a TB10.
Above 150 spread on EGT for a O-360 is rather uncommon, I’d say there is something wrong, indeed. As said, I’d go for baffles and carb gaskets first. Was this example a steep climb? Excessive AoA and misaligned baffles maybe? Don’t worry, you’ll find out.
In order to better understand what is going on, you need to tell us which events happened at each relevant point in the graph: throttle movements, RPM change if CS or due to levelling off, and leaning, but not just the latter. Altitude changes are also relevant if significant.
On a carburetted engine there is not much you can do to affect mixture distribution. Since you cannot change individual fuel flo, all you can do is affect individual airflow.
The three typical items that will affect airflow differentially are:
-Induction air leaks. These are easy to diagnose because the issue all but dissapears with a full-open throttle (assuming NA as your case) . It is not about how much power the engine is delivering (RMP or MP or altitude) but what is the position of the throttle. A small leak will affect mixture with a partial throttle.
-Exhaust leakages (easier to visually inspect for than inlet) or blockages (typically broken parts inside exhaust mufflers or heat exchangers). You need a very significant leak or blockage to cause a major mixture maldistribution.
-Cylinder induction valve not opening fully due to cam wear. Easy enough to check during regular maintenance by removing head covers and measuring valve lift.
Without the information at the start of this post it is impossible to tell.
However, being practical, has anything changed in the operation of your engine before vs after you installed your engine-monitoring GI-275? If not, and there are no other concerns, do not worry unduly simply because EGT traces are weird…hopefully the engine is still the same as before!
Here’s an initial climbout followed by a shallower, longer climb at higher speed:
I won‘t go into whether it is good or not to lean so significantly at the start of the climb. But what is interesting is that the spread“ starts getting bad only after the leaning. Before, it is decent. So at least short term you can solve the problem by not doing so. Do it only once the EGTs habe dropped and then lean only to bring em back to where they where (constant EGT method).
Antonio wrote:
On a carburetted engine there is not much you can do to affect mixture distribution.
One trick that can make it a bit more uniform is to turn on carb heat. It’s obviously not a real solution, but you can at least use it for diagnostics, and also when cruising LOP WOT.
