Lycoming IO-540 EGT split side to side

70 hours since purchasing our RV-10 (370 TT). The savvyanalysis data has shown an EGT split in every flight.

One flight, very similar to other flights, show Cyl 2/4/6 EGT’s are 1392F - 1443F and 1/3/5 are 1277F - 1326F.

Others have suggested the possibility of low fuel flow issues on the 2/4/6 side and/or high fuel flow on the 1/3/5. How would that occur? Also mentioned was the possibility of a partially blocked muffler on the 2/4/6 side.

Wanted to get input from the knowledgeable folks here as to whether this is an issue at all or if so what steps should I take going forward.

Thanks,

absolute values are not always helpful

Tom Delaney said:

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One flight, very similar to other flights, show Cyl 2/4/6 EGT’s are 1392F - 1443F and 1/3/5 are 1277F - 1326F.

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Most experts say that the absolute values are not that important, what's important is how the move - are they all reaching peak when you lean at the same time? If so, that's good.

Differences can come from many things like the length of the wires to the sensor and the position of the sensor on the exhaust stack.

Check with the help section on the savvy website - I think he explains this. If not, he does in his books.

https://resources.savvyaviation.com...ticles_eaa/EAA_2010-10_egt-myths-debunked.pdf

That is an interesting asymmetry. Suggestions to gather more data:

1. Mixture distribution test and induction leak test: https://resources.savvyaviation.com/in-flight-diagnostics/

Are the cylinder EGTs peaking together?

2. Are the EGT probes on the exhaust pipes installed the same distance from the cylinders on both sides? Variability in EGT probe location could change EGT value.

Tom,


My suggestion is to first take a look at your fuel flows on each cylinder as you lean in flight. You need to go fly at 8-9K ft or so and determine the fuel flow spread between the cylinders as a first step. If they all peak with in .5gph flow, then you probably don't have an issue, other than trying to get them a bit closer if you want to run Lean of Peak.



Do your logs show an entry where the previous owner or builder flow matched the fuel injectors?


Simply looking at the relative EGT's does not tell you much. The installation location of the probe can have a dramatic affect on the readings. The leaning test will tell you if you truly have an issue.


What are the genetics of your engine? new Lyc, Aerosport?

Thanks for the suggestions!

All EGT probes are installed the same distance from the cylinders.

I have performed a mixture distribution test a few times however my results are suspect because the Skyview fuel flow indication is unstable. The FF constantly varies over 1.0 GPH. My best interpretation of the data resulted in the spread being anywhere from 0.6-1.2 GPH. Seems like I should get this figured out first but unsure how to proceed. Suggestions welcomed.

There is no indication that the injectors have been previously tuned. I did swap the #1 and #2 injectors to see if anything change and it did not. Both injectors had the same marking on them for what that is worth.

The engine was a new Lycoming from Van’s when installed in 2016 and now has 370 hours.

Thanks,

Tom Delaney said:

Thanks for the suggestions!
The FF constantly varies over 1.0 GPH. My best interpretation of the data resulted in the spread being anywhere from 0.6-1.2 GPH. Seems like I should get this figured out first but unsure how to proceed. Suggestions welcomed.

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It is common to have erratic fuel flow indications with the fuel flow sensor located in the tunnel between the front seats. I fixed this by moving the fuel flow sensor (red cube) from the plans-depicted location in the tunnel to the engine compartment, suspended midway in the fuel line between the fuel servo and the spider.

Page 20 of install manual depicts what I did: https://iflyei.com/wp-content/uploads/FP-5L-II.pdf

https://vansairforce.net/community/showthread.php?t=100837

I fire sleeved the fuel line and wrapped fire sleeve around the red cube. Rock solid fuel flow now.

The FF sensor needs to be located between the fuel servo and the fuel spider. That’s where most are locating it. This will cure your fluctuations and also help with the general flow of fuel on the suction side of the mechanical pump
You don’t need to swap the entire injector, just the restrictor orifice that sits inside the injectors. With the fluctuations you have now, it would be a waste of time to try to flow match the cylinders.

EGT probe position

Tom,
You said that the EGT probes were the same distance from the cylinder. However, you didn't mention the position. If you want the probes in the same relative position then if the probes are installed on the aft side of the exhaust pipes on one side of the engine then they need to be installed on the forward side of the exhaust pipes on the other side of the engine.
Based on your temperatures I'd guess that your EGT probes all are installed on the same side of the exhaust pipes (i.e. all installed on the aft side of the exhaust pipe).

Hi Norris,

Your description is how the probes were installed - all angling aft. Not familiar with this concept but that does not mean anything. Food for thought. Thanks,

To continue this thread, I am in the process of relocating the red cube to smooth out the fuel flow fluctuations and then I will run the suggested tests again.