AAflyer

AAflyer

Well Known Member
I've got about 35 hours on my new AeroSport IO-360 with dual PMags. It's running pretty darn well..until I start trying to lean it below 'peak'.
Almost as soon has I get the last cylinder to peak...which is only about 40 degrees behind the others...the engine loses significant power. It doesn't really run 'rough'..it just bogs down A LOT.
I'm not quite ready to practice my in-flight engine re-start procedures, so I always chicken out and advance the mixture.
If this helps...I really don't get much of an RPM rise when I kill the engine by pulling the mixture to ICO.
Any thoughts?
P-Mag "curve"?
Mixture setting at fuel servo?

Thanks in advance.
 
When I go from ROP to LOP I always lose some RPM. In most cases its around 100 RPM, once in awhile a tiny bit more.
In the idle condition, when fully leaned RPMs should rise around 40. If it is more than that, your idle mixture is likely too rich.
 
180hp or 200?

What is total fuel flow when the first cylinder peaks? Total fuel flow when the last cylinder peaks?

Are you running with the pMag jumpers in or out?

Carl
 
AAflyer said:
...I'm not quite ready to practice my in-flight engine re-start procedures, so I always chicken out and advance the mixture...
Click to expand...

Just so you know, advancing the mixture IS the "restart procedure" in this scenario.


As for the other thing, there is a loss of power when going LOP - how much depends how far you go, and THAT depends on the FF spread between the first and last cylinders to peak.
 
40 degrees seems like a lot. If I understand what you meant, that when the last cylinder peaks, the first one or more are already 40 degrees lean of their peaks. Thats kind of a marginal spread for useful LOP. That one that leans last, (its richest) you could try putting a slightly smaller injector in that cylinder. If you have 0.028" injectors (the most common) then try an 0.0275" or 0.0270". They are $27 each from Don at Air Flow Performance. buy a couple of each. Only change one cylinder at a time, and repeat your leaning test.

I should say though, that before you do much else, you really should do the classic GAMI test and write down what you have, so you can really see that the other cylinders are much leaner, and where they stand relative to each other.

It is normal to get some power loss as you go lean. If you are making really small changes (0.1 gph at a time) you will hardly notice. If you do it all at once, then yeah, you will hear the engine power drop off.
 
Balancing the injectors is a good idea, but it really is an efficiency thing, not a performance thing. Right now, that last cylinder is running at peak, not 40 LOP like the others. Once you balance it, it will produce less power like the others and total power output will drop a small tad as will the FF. If your cylinders don't peak at the same time, you are throwing extra fuel at the rich ones without any real benefit. This situation also leaves the rich cylinder with a higher ICP. That cylinder is not getting the detonation margin benefits of running LOP. It's ICP will be higher, putting more stress on the cylinder and decreasing detonation margin.

40* LOP will produce a good bit less power than peak or best power. You need to qualify "really bogs down" and "a LOT."

Measure your RPM and TAS at Peak or best power (wherever you have it that is is not bogged down) and then again at 40* LOP and post here. The group will tell you whether or not that is consistent with the norm.

Larry
 
I would agree that you need to balance your injectors. 40 degrees LOP is quite lean on the leanest cylinder(s). Usually best economy is around 25 LOP. That's why your engine is losing power. If you balance your injectors you should be able to get the richest cylinder to peak with the others so you can get them all 25 LOP around the same fuel flow and will not lost as much power. It will be noticeably slower and less powerful, but the decrease in fuel flow will greatly make up for it.
 
40 degrees behind the others is fine but you should be watching a differential in fuel flow from when the first one peaks until the last one peaks.

If your ff is more than .5 gph, then you need to balance your injectors.

After you get your phase one done, come up this way ( or I could come down your way) and we can compare notes if you like.

If your ff is less than .5 gph differential... then you are fine.

:cool: CJ
 
Carl Froehlich said:
180hp or 200?

What is total fuel flow when the first cylinder peaks? Total fuel flow when the last cylinder peaks?

Are you running with the pMag jumpers in or out?

Carl
Click to expand...

Fuel flow vs egt's is the key here as Carl wrote. The magnitude of peak EGT temperatures are not too relevant in directly comparing one cylinder to another.

They are extremely relevant in comparing where the cylinders' peaks are (per fuel flow) vs the other cylinders.

If your engine is running smoothly but losing significant power as you go lean, it sounds to me like the injectors are reasonably balanced.

There has been lots of good advice in this thread already, but there are tons about this in the archives.
 
lr172 said:
Balancing the injectors is a good idea, but it really is an efficiency thing, not a performance thing. Right now, that last cylinder is running at peak, not 40 LOP like the others. Once you balance it, it will produce less power like the others and total power output will drop a small tad as will the FF. If your cylinders don't peak at the same time, you are throwing extra fuel at the rich ones without any real benefit. This situation also leaves the rich cylinder with a higher ICP. That cylinder is not getting the detonation margin benefits of running LOP. It's ICP will be higher, putting more stress on the cylinder and decreasing detonation margin.


.

Larry
Click to expand...

If your cylinders peak at radically different fuel flows, and .3 a .4 is enough to cause a really rough engine, then it's not just efficiency we're talking.

Say number 3 peaks at 9.0 gph andnumbers 1,2 and 4 peak at 8.7 gph. By the time you get 1,2,& 4 to run LOP, number 3 will be running so lean it will probably be missing or popping.

Take the OP should take down his FF numgers and do it right andhis problem will most likely go away.
 
RV8iator said:
If your cylinders peak at radically different fuel flows, and .3 a .4 is enough to cause a really rough engine, then it's not just efficiency we're talking.

Say number 3 peaks at 9.0 gph andnumbers 1,2 and 4 peak at 8.7 gph. By the time you get 1,2,& 4 to run LOP, number 3 will be running so lean it will probably be missing or popping.

Take the OP should take down his FF numgers and do it right andhis problem will most likely go away.
Click to expand...

I suspect your situation was unique to your setup as mine maybe to my situation. My initial FI installation was just like the OP's. One cylinder peaked about 40* after the others. When I took the engine to 50 or 100* LOP it was smooth as could be (I do have EI, as the OP does, and that makes a difference). My spread was about .4 GPH. After balancing down to .1 GPH, I find no noticeable improvement in smoothness or performance, though my FF was down a bit for the same LOP performance.

I had a carb before the FI with TERRIBLE distribution and felt no roughness when leaned to 40 LOP (only two cylinders actually at that level).

I would also say that with imbalanced injectors, the better practice is to lean the first cylinder to peak at your target LOP setting, not the last to peak for the exact reasons that you state. This was my efficiency point. The trailing cylinders are all richer than the target, therefore wasting fuel. If you take the first peaking cylinder past your target, you can get roughness, as the power level falls off pretty quick after about 50 LOP and the imbalanced power becomes more noticeable as you fall down that curve with wider and wider spreads in power produced.

Larry
 
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