Why do my EGTs spike on landing?

Checkout_my_Six said:
Do you have an altitude compensating fuel pump? Your mixture is getting leaner in your descent.
Click to expand...
It's a carbed Continental. Those compensating fuel pumps are on injection systems.

I have seen the O-540 go lean as the throttle is closed, and lean means rising EGT. If it went rich the temps would go down.

I don't think the MA-5 carb has a power enrichment valve. If it did, it might be misrigged. The more likely things to look at are vacuum leaks and the idle mixture setting.
 
No altitude compensating fuel pump to my knowledge. Besides, it's just a 1k ft descent from pattern altitude.
 
A couple of people have suggested electrical issues but I don't see a response from the OP.

In no special order -

1.
When you close the throttle lever not only does the engine throttle valve close affecting the manifold pressure but the engine RPM drops too. Could the cause be related to the generator dropping off line or reducing output? If a voltage reference or a reference junction in the monitoring box wasn't working properly I can imagine something like this occurring.

2.
Also see note in thread about grounding the monitoring box directly to the engine and not elsewhere.

3.
You mention the possibility of RF interference. Again, the generator speed changing could well change the RF environment.
 
If it were an electrical anomaly, why wouldn't all functions of the JPI be affected? The CHTs remain rock stable, as are all of the other measurements. I don't see how grounding, RFI or any other electrical situation could affect only the EGTs while the balance of the the measurements are stable.

I thought I posted the traces last night, but I don't see that post now.
 
LesGawlik said:
If it were an electrical anomaly, why wouldn't all functions of the JPI be affected? The CHTs remain rock stable, as are all of the other measurements. I don't see how grounding, RFI or any other electrical situation could affect only the EGTs while the balance of the the measurements are stable.
Click to expand...


I thought I posted the traces last night, but I don't see that post now.
Click to expand...
https://www.pilotsofamerica.com/com...my-egts-spike-on-landing.140363/#post-3327660

So, your temps were high during the descent then leveled back down on the ground. I would assume that your RPM was higher during the descent than it was on the ground. And, the manifold pressure was lower - correct?

In my (automotive) mind, that all points to slower combustion which raises EGT.
 
It may have been higher than when I was on the ground at idle, but it was most certainly lower than at cruise where the EGTs weren't as high. On descent I was not much higher than idle on RPM, and MP was low.
 
I'm at sea level, so I lean aggressively on the ground. The idea being that if the mixture is very lean, not only do you avoid fouling, but if you forget and apply takeoff power without richening the mixture, the engine will stall out.
 
Capt. Geoffrey Thorpe said:
In my (automotive) mind, that all points to slower combustion which raises EGT.
Click to expand...
In aircraft engines, that can be caused by a weak mag. Weak spark won't ignite a lean mixture such as you can get with the throttle closed and the wind driving the prop. The idle circuit has tiny passages that can only supply limited fuel.
 
In speaking with a long-time IA, he said it sounds like the prop is overdriving the engine. That makes sense. First, all I have to do is add a few hundred RPMs and the EGTs drop right back down. Second, the rest of the flight is all normal, so I don't see electrical gremlins as a cause.
 
LesGawlik said:
In speaking with a long-time IA, he said it sounds like the prop is overdriving the engine. That makes sense.
Click to expand...

That was my assertion (see post # 21) but as I stated then that wouldn't necessarily explain it if it's a new phenomena or intermittent.
 
LesGawlik said:
In speaking with a long-time IA, he said it sounds like the prop is overdriving the engine. That makes sense. First, all I have to do is add a few hundred RPMs and the EGTs drop right back down. Second, the rest of the flight is all normal, so I don't see electrical gremlins as a cause.
Click to expand...
When were the mags last off for internal inspection?
 
Yes, and I think you were right. It was intermittent only to the extent that it occurred only in one distinct phase of flight.

Also, I often leave the prop out as long as possible. If I push the prop in early I think it is more likely to windmill and drive the engine.
 
You must log in or register to reply here.
Back
Top