What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

EGT Drop

RV7AJeremy

RV7AJeremy

Well Known Member
Hello all,
I have had an issue now on three separate flights where EGT4 had dropped about 300*F when I have gone to idle while slowing to get my flaps down. I have noticed no roughness, nothing else abnormal, and I would never have noticed anything was unusual if I had not had this engine monitor. As soon as I add any power everything returns to normal.

Here are the links to the three flights:

https://www.savvyanalysis.com/flight/904240/fe8ef1ce-4cc2-4b68-b2ae-f78778d72571
Event at 1:10:56

https://www.savvyanalysis.com/flight/904241/a64648b5-027c-42b1-8b2f-d85163eaee2e
At 0:25:45

https://www.savvyanalysis.com/flight/865081/5a22da28-6cd1-4d6d-904d-d2c35cac0c52
at 1:08:52

Any comments appreciated.
 
When you do a mag check, watch all 4 EGT's. They should all go up when on only one mag. If not, then you may have a bad plug. Otherwise, it could be an idle mixture thing, somehow getting too much fuel to that cylinder. See if you can get it to repeat on the ground. Another thought is to switch both plugs from 2 to 4 and see if the event stays with the cylinder or follows the plugs.
 
Bill.Peyton said:
I would check for a vacuum leak, or the possibility of two dead plugs
Click to expand...

Bill, can you expand on the "vacuum leak"? I do not have a vacuum pump.

Jesse said:
When you do a mag check, watch all 4 EGT's. They should all go up when on only one mag. If not, then you may have a bad plug. Otherwise, it could be an idle mixture thing, somehow getting too much fuel to that cylinder. See if you can get it to repeat on the ground. Another thought is to switch both plugs from 2 to 4 and see if the event stays with the cylinder or follows the plugs.
Click to expand...

All the plugs check ok during the mag check. (I have had fouled plugs before)

Could this be an injector nozzle issue?
 
It could be an injector nozzle that is partially clogged, but I would think it would show up all the time. You could also swap restrictors from 2 to 4 and see if it follows the restrictors or stays with the Cyl. Make sure to do that separately than other tests.
 
You do have a vacuum pump . .

When you close the throttle, the engine becomes a vacuum pump - thus lowering the manifold pressure. So - with a low MAP, if there is a leak if the intake tube gasket/ o-ring etc, then it would lean out that cylinder. Thus, a vacuum leak.

Good luck!
 
The vacuum leak I speak of would occur in the intake manifold. When you reduce the throttle to idle, you close the throat of the fuel servo, this causes the pressure in the intake manifold to decrease as compared to the static pressure surrounding it. If you have a leak in the intake system on one particular cylinder, it will cause that cylinder to run leaner than the rest of the cylinders . At idle this will become most noticeable. Check the intake manifold gasket at the cylinder head.
 
BillL said:
When you close the throttle, the engine becomes a vacuum pump - thus lowering the manifold pressure. So - with a low MAP, if there is a leak if the intake tube gasket/ o-ring etc, then it would lean out that cylinder. Thus, a vacuum leak.

Good luck!
Click to expand...

Got it! Thanks
 
Except that if you started rich of peak, an intake leak should show a rise in EGT. If you're 300 deg lean of peak I'd think you'd feel the power imbalance.
 
Since the OP mentioned not noticing any roughness I would tend to discount an intake leak leading to an over lean condition that puts the flame out in the cylinder.

First thing I would do is switch EGT probes on cylinders 2 & 4, if possible. If the problem follows to 2 then it is something about the probe. If it does not follow, the problem is in the cylinder. From there it is a matter of trying some of the things suggested here already.
 
BobTurner said:
So then we need to know: does the egt sit steady at 300 low, or is it falling until you put power back in?
Click to expand...


You guys are great! Thanks for the help:D

The EGT just drops momentarily (only on #4); todays flight it went from 1355 to 1090 then back up to meet the rest of the cylinders, all over a 15 sec period. I actually didn't notice this in the airplane and only noticed it on the data analysis that I do after each flight. The times that I have noticed it in the plane, I have always thought a probe or sensor issue because there are no other indications, she just keeps running smooth as can be.

However, now that I have several instances of it happening, it is always at the same time, near the end of a flight, as I reduce power to idle.

I will swap probes before the next flight to see if the issue stays with the probe or the cylinder.

Another question, do the links in the original post work for anyone else?

Thanks everyone!!
 
One additional thing: It does not happen on every flight. I was out practicing ELP's (emergency landing patterns) the other day, had the power at idle for extended periods of time (2min each pattern), and all the EGTs stayed together though out multiple patterns. Engine has roughly 43 hours on her now (certified superior vantage engine). Thanks again.
 
You must log in or register to reply here.
Back
Top