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Cause for two cylinders running cold when LOP

Fred.Stucklen

Well Known Member
I'm having and issue with a new IO-360-B1B engine that I don't understand. When running ROP all temps appear to be within reason See Test 3.png below). But when I run LOP cylinders #1 and #3 CHT's start getting cold (over 50* deviation - see Test 1.png ,BUT the EGT's don't fall as expected. After a short time the engine starts getting rough like #1 & #3 are mis-firing. What would cause two cyclinders CHT's to deviate downward (and not the rest) with the EGT's staying relatively constant, when LOP but not ROP?

I've tested all the temp prob's and they are accurate.
 

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  • Test 1.png
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Do a couple of data runs to measure GAMI spread. Use the data to balance the injectors. Replacement injectors are available from AirFlow Performance (~$30 each).

If you have a weak ignition this could aggravate LOP operations, but you will figure that out doing the GAMI spread.

Carl
 
Do a couple of data runs to measure GAMI spread. Use the data to balance the injectors. Replacement injectors are available from AirFlow Performance (~$30 each).

If you have a weak ignition this could aggravate LOP operations, but you will figure that out doing the GAMI spread.

Carl
The GAMI spread came out at about .1 when running ROP. I'm also running two PMAG's so the timing is another variable, but should be the same on all cylinders. I still can't explain why the EGT's stayed constant when running LOP....
 
The GAMI spread came out at about .1 when running ROP.
This statement does not make sense. GAMI spread is fuel flow first cylinder EGT to peak to fuel flow last cylinder EGT when going LOP.

The ignition aspect can be eliminated doing an in flight mag check. EGTs will go up on any cylinder not firing on both plugs.

Carl
 
This statement does not make sense. GAMI spread is fuel flow first cylinder EGT to peak to fuel flow last cylinder EGT when going LOP.

The ignition aspect can be eliminated doing an in flight mag check. EGTs will go up on any cylinder not firing on both plugs.

Carl
Carl, you are correct. The GAMI check was at ROP. There's no way to get it at LOP.....

I will be doing more flight checks this week to verify the GAMI spread again.
 
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SO here's all the data in one screen. GAMI ratio is still .2.... Why does cylinder #1 & #3 CHT fall off????

I see from Airflow Performance documents that they have a method of indicating the size of the injector nozzles. Does anyone know how Lycoming indicates nozzle sizes (as that is what I have in my engine) ???

Test 5.pngTest 6.png
 
If your GAMI spread is 0.2 GPH, that would seem to point to something other than the fuel injection nozzles. Run the other tests that Mike Busch references, with special attention to the in-flight mag test when running LOP at altitude.
 
The GAMI check was at ROP. There's no way to get it at LOP.....
One of us is misunderstanding the GAMI check…

The “GAMI check” is neither ROP or LOP - it’s AT peak. It’s the fuel flow spread between the first cylinder to peak (whatever number that one is), to the last cylinder to peak (whatever number that one is). The value of the EGT is irrelevant - you only need to identify the FF at the peak events.

If the cylinder is misfiring and EGT is falling off, it’s simply not getting enough fuel or the spark isn’t cutting it. Have you done an ignition check while up at altitude and LOP? That will also uncover ignition issues.
 
I'm having and issue with a new IO-360-B1B engine that I don't understand. When running ROP all temps appear to be within reason See Test 3.png below). But when I run LOP cylinders #1 and #3 CHT's start getting cold (over 50* deviation - see Test 1.png ,BUT the EGT's don't fall as expected. After a short time the engine starts getting rough like #1 & #3 are mis-firing. What would cause two cyclinders CHT's to deviate downward (and not the rest) with the EGT's staying relatively constant, when LOP but not ROP?

I've tested all the temp prob's and they are accurate.
Do a mag check LOP in flight. That will tell you everything. $10 says it is plugs. You don't say the brand of plugs, age, hours.
 
One of us is misunderstanding the GAMI check…

The “GAMI check” is neither ROP or LOP - it’s AT peak. It’s the fuel flow spread between the first cylinder to peak (whatever number that one is), to the last cylinder to peak (whatever number that one is). The value of the EGT is irrelevant - you only need to identify the FF at the peak events.

If the cylinder is misfiring and EGT is falling off, it’s simply not getting enough fuel or the spark isn’t cutting it. Have you done an ignition check while up at altitude and LOP? That will also uncover ignition issues.
The charts above is what I'm doing. ROP to LOP to get fuel flow at each cyclinder EGT peak. The problem I'm having is that running LOP two cyclinders CHT's are cooling down significantly WITH NO CHANGE IN EGT's.

I'll run Mike Bush's test this week to rule out ignition issues. The engine has 20 Hrs on it so should be broken in by now. The plugs were new NGT BR8...
 
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So here's the results of the additional tests for ignition problems, and LOP operation. When running LOP I was not able to duplicate the same CHT differences. I think I've come to the conclusion that it was just a product of breaking in the engine. The ignition test looks normal to me (comments welcome). the LOP operation was very smooth all the way down to multiple cylinders starting to cut out, so no complaints there.

Ignition Test & LOP test

Here's a picture of the Ignition test results.
Test 7.png
 
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