IO360 fuel distribution instability

Some fuel distribution issues have been bothering me lately. After matching the injector nozzles, I have been operating lean-of-peak for a number of years with no problems. However, lately I have been experiencing some strange fuel distribution issues. The engine is an AeroSport Power IO 360M1 with Hartzell constant speed prop, Electroair ignition on the right magneto pad supplying spark to the top plugs, and a P-Mag on the left magneto pad supplying the lower plugs. A typical FF/EGT/CHT spread is:

Altitude: 12000
OAT: 58 degrees F
Fuel Flow: 6.7 GPH
CHT #1: 352? EGT #1 -47? (from peak)
CHT #2: 338? EGT #2 -54?
CHT #3: 372? EGT #3 -34?
CHT #4: 373? EGT #4 -32?

At times when initially setting the mixture for lean of peak, the distribution will split, with the #4 cylinder going much richer:

Altitude: 12000
OAT: 58 degrees
Fuel Flow 6.7
CHT #1: 375? EGT #1 -25?
CHT #2: 365? EGT #2 -55
CHT #3: 365? EGT #3 -45?
CHT #4: 385? EGT #4 -15?

The CHT and EGT seem to be in correspondence: EG- the highest CHT cylinder has the richest mixture as shown by the smallest drop from peak. The distribution seems random, and sometimes changes during the flight by itself. Sometimes going back to rich of peak, then resetting LOP fixes the distribution.

Does anyone have any idea what is causing this? Is it a case of dirty injectors or a problem with the flow divider? What might be the solution?

Thanks to all for your thoughts.

The first thing you need to look at is your GAMI spread (fuel flow of the first cyl to peak vs the last). This will tell you how balanced your injectors are.

If they are balanced, then you could have ignition issues, EGT probe issues, or other things.

If they aren't balanced well, then you look at the fuel system.

--Ian Jordan
Dynon Avionics

Hey Craig,
As Ian says the GAMI spread is more important than these other numbers.

I also suggest using https://www.savvyanalysis.com/home for a free service to chart your results. Very informative website.

Fuel divider

I'd consider checking the fuel divider and lines . If you have some trash or an obstruction in #3 it could manifest itself this way. This is a balancing act so fuel diverted from 3 could make 1 and 4 richer.

These number vagaries could simply be the result of a little chaos in the Lycoming world.

I'd try starting over from full rich and see if it is different. I bet it will be. These engines are not all that predicable when looking at numbers that closely.

There was a time when that was not possible or of consequence.

If the engine is running smooth and all else is normal, press on.

Are these two conditions at the same throttle setting? On my aircraft, with IO-360-A1B6, I find that the cylinders reach peak EGT almost simultaneously, if I?m at full throttle. But, if I?ve pulled the throttle back a bit, I get a much larger difference between cylinders. I?ve never understood it, but I usually cruise at full throttle, so I haven?t worried about it much.

Fuel distribution instability

Thanks everyone for your thoughts. For the record 1) all readings have been at WOT, 2) the gami spread is .2 Gph and 3) when the imbalance occurs, the problem can usually be corrected by going full rich, and then going back to Lean of Peak.

EGT imblance is not the point, but my observation is that if your spread is 0.2GPH typically, then this is good. But what you may be suffering from is an intake leak upsetting the F/A ratio's and some leaks for some reason are random in the amount of leakage from one time to another

Also I think your LOP ops should be yielding lower CHT and I figure you are running too much advance.

YMMV

Although unlikely in a known good system, a contaminant could be "floating" around in the fuel divider. A buddy of mine had this happen. Symptoms where much more severe, a complete loss of one cylinder, from time to time, then a different cylinder, and so on. The piece of debris was large enough to cut off the fuel flow to the injector line, then it would move around after shut down. Sometime show up, sometime not. While it seems obvious, it was very difficult to troubleshoot.

I think this is a long shot but if you run out of things to check....

Talk to Don Rivera at Airflow Performance.

I'm pretty sure it's the overall low fuel flow. At flows that low, the flow divider is playing a bigger part than the nozzles. Because I live at high altitude and routinely fly LOP at high altitude, Don had me switch all of my injectors nozzles to smaller orifices. This raises the fuel pressure at the divider and brings it back out of the equation.

I wouldn't do full power takeoffs on cold days at sea level because of this change, but I've never had the opportunity to try anyway. Landing at DA less than 6000' feels really strange to me.

CHT, Timing and FF divergence

Dave Brown: Thank you for catching the high CHT and its possible relationship to timing. When I received my rebuilt engine from Aerosport Power, they suggested an initial ElectroAir timing point of 20 degrees, which I set on the ElectroAir module. I have noted that on the ignition check that when the ElectroAir was turned off that there would be a consistent 30-40 rpm drop. The drop when the P-mag was shut off was 0-10 rpm. I attributed this to differences in timing programs between the ElectroAir and P-Mag (P-mag on Schedule ?A? 34? advance max). To test your idea, I retarded the initial timing by 4? (16? initial timing) on the ElectroAir module, and test flew the aircraft this morning. On the ignition check at 1800, there was no drop when the Electro Air was shut off, and 20-30 rpm drop when the P-mag was shut off. This reverses what I had been noting earlier. On the test flight (somehow I lost the Dynon data for this flight) at 12000?, LOP by 35?F I noted that the CHTs were running about 20-25 degrees cooler with the retarded ElectroAir timing. However, at 12000? altitude and LOP, when shutting off the ignitions one at a time I noted that the EGT increase was about 60? more when the P-mag was shut off than when the Electro Air was shut off. I would suspect that this indicates that I have retarded the ElectroAir too much. I have reset the ElectroAir to 18? and will test fly that configuration. I also noted that the LOP fuel flow distribution was fine! No divergence!?!

Dave, I would appreciate any thoughts you might have on my analysis.

?Rocket? and JonJay: Thank you also for your thoughts. I am flying out of Pagosa Springs CO, with a field elevation of 7600?, but fly to the Dallas area and Midwest frequently, so I need to have the nozzles set for sea level capability. I need to learn more about the flow divider. I am reluctant to take it apart until I have a firm knowledge of it. Perhaps Don at Airflow Performance can give some advice; the flow divider may have to be sent to him for checkout.

Posts will be made of anything new that I learn. Cannot fly till Sunday, but will post the results of my next flight.