EGT keeps increasing when leaning

I have replaced both Slick mags and spark plugs during my recent condition inspection. The mags are timed to engine at 25 deg BTDC as indicated on the engine data plate, same as previous timing. The engine is IO-360-M1B, I could do LOP before CI. Engine runs fine ROP (I typically setting for short local flights) after the CI. But in last flight when I tried to do LOP, EGT on all cylinders just wouldn't drop when leaning. The EGTs kept going up and up to 1600Fs, and engine started running really rough, but the EGT will not drop. I know the engine is definitely running LOP based on fuel flow rate, but why I didn't see EGT drop. The leaning was done between 45%-55% power setting. What can cause this? I had the injectors cleaned during CI. I will double check the timing, which I already did before putting the cowls back. The mag checks are fine, both ground and in flight.

It sounds like when your cleaned one or more of the injectors you lost injector nozzle(s).

Do not fly the plane before pulling the injectors to verify.

Carl

Did you pass a mag check? I once lost a mag in flight and had the exact same experience/symptoms. The mag is especially suspect in your case due to the mag replacement. Might consider an in-flight mag check.

Larry

Just checked the pictures I took after installing the injectors, no missing nozzles. And if nozzle is not there, it is not likely the fuel line will seal with the injector. I will double check, but I doubt that is cause. It happens on all cylinders, that puzzled me. I know when installing injector, the "V" mark should be at the bottom, I didn't make sure the "V" mark is at the absolutely lowest point during installation, but they are definitely at the bottom. Will that cause the ever increasing EGT problem?

Yes, the mag check is fine both on ground and in flight. The rpm drop is about 110rpm, the difference between two mags is about 20 rpm. I did notice that during in flight mag check, the EGT on cyl#1 is about 70F higher when on left mag compared to when on the right mag.

Retarded timing. Timed at the TDC mark rather than the 25 BTDC mark, or timed without tripping dual impulse couplings.

Retarded timing pushes the PV diagram to the right. Pressure and EGT is higher at exhaust valve opening. Leaning shifts it further to the right.

Thanks for the input! I went to hangar yesterday, and checked the fuel injectors and timing, they are all ok. Then went for a flight to do LOP again. What I found is that I will see EGT drop if I move the mixture VERY SLOWLY, maybe a few degress at a time. In that case, the EFIS system will be able to show LOP. If I keep leaning slowly, to certain point, the EGT will jump up and engine will start running rough. I can get 15-20deg LOP if I lean SLOWLY before one EGT starts increasing again and engine starts running rough. I guess I will just have to lean very slowly.

seattleworm said:

Thanks for the input! I went to hangar yesterday, and checked the fuel injectors and timing, they are all ok. Then went for a flight to do LOP again. What I found is that I will see EGT drop if I move the mixture VERY SLOWLY, maybe a few degress at a time. In that case, the EFIS system will be able to show LOP. If I keep leaning slowly, to certain point, the EGT will jump up and engine will start running rough. I can get 15-20deg LOP if I lean SLOWLY before one EGT starts increasing again and engine starts running rough. I guess I will just have to lean very slowly.

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If you have been flying this airplane for long enough to know what is normal, and that now after doing some work to the engine it doesn't act the same, you really aught to figure out what has changed.
It could be trying to tell you something, that if ignored could have bad consequences.

Thanks Scott for the reminder! I have been trying to figure out why. Things changed during CI are: Mags replaced, plugs replaced, injectors cleaned, idle mixture being adjusted very slightly. Other than these, nothing else changed. Engine runs fine without noticeable difference other than now I need to lean very slowly to let EGTs stabilize before further leaning. Fuel flow at the expected LOP is more or less the same (within 0.1g/hr). One good thing I see is improvement of GAMI spread. Before all the changes, I saw GAMI spread is about 0.4-0.5g/h, now when I lean slowly, I got 0.1-0.2g/hr, and the engine does feel smoother. But, again, I need to lean slowly to capture the EGT drop, otherwise I get to a rough running engine without capturing the EGT drop.

Any suggestions on what else I need to check to ensure the engine is healthy? Borescope didn't show anything abnormal, compression check is consistent with previous numbers. I sure don't want to miss any hints that can prevent a bigger issue. Thanks!

Try measuring the fuel coming out of the injectors (small bottle at each cylinder) and see if you can reproduce the varying fuel flow on the ground.

Two things to ponder. 1.) After the CI what made the egt so sensitive? 2.)When leaning slowly and you get LOP, the egt should not at any point increase with increased leaning it should only go down, not up, once you are past peak and continue leaning in a normal combustion scenario. Could it be pre-ignition or detonation?
Did you change adjust the the mixture linkage during the inspection, causing the mixture arm at the servo to move faster than before? Is it possible that some how during its travel it is moving toward rich when the cockpit control is moved lean for part of its travel?
Something isn't right here...
Good Luck,
Mahlon

you mentioned that the injectors were cleaned. Were they all put back into the same injector bodies as before? That might explain why the lean spread has changed.

Tom Martin said:

you mentioned that the injectors were cleaned. Were they all put back into the same injector bodies as before? That might explain why the lean spread has changed.

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Yes, they were put back in the same injector bodies, and back to the same cylinders. I think the cleaning and new plugs made this change (or improvement?). The old plugs did get worn out pretty badly with out of spec gap (didn't regap in 400 hours).

The EGT rise after initial drop has been always there since engine was new from factory. I don't know why. but when EGT rises again, the engine will start running really rough, so I rarely go there and almost forgot about that.

seattleworm said:

The EGT rise after initial drop has been always there since engine was new from factory. I don't know why. but when EGT rises again, the engine will start running really rough, so I rarely go there and almost forgot about that.

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My YIO-360 M1B (13hrs) from vans -all stock does the same at 2600-2700. I will add a graph to show it. Leaned slowly too. It does lean nicely at 2400 and lower. All tested at 8500 ft a couple of days ago.