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Fuel flow fluctuation

At cruise, 10,500 + or - 1000 fuel flow fluctuated between 9-14 GPH. Both on the original pressure type FF and the Fuel Scan 450M. Also I can hear the engine surge. I have 470L engines.

Where do I start to find the problem?

Model: Baron E55
Posted 7/27/2023 - 7 months ago
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A little more information would be good.

Is this a symmetrical fluctuation (meaning target FF is 11.5)? How much is the MAP swing? Does an increase / decrease in either MAP or FF dampen or eliminate? How about an RPM change? What is your TO fuel flow? And what is the age of the fuel system components, or engine, if original to the engine?

Mike
ABS Technical Advisor

Posted 7/27/2023 - 7 months ago
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Symmetrical ....Yes. + or - 3gph
No MAP or RPM swing. But I can hear it surge.
If I reduce power or operate at lower altitudes I do not see a fluctuation
The engine is about 17 years old. So is the fuel pump.
I had the throttle body rebuilt 2 years ago and it has about 200 hours on it.
Aircraft ser # TC 2288 95B55
TC 3A16
The throttle is split at lower altitude to maintain even MAP and RPM. ie: While in the traffic pattern, landing. The left throttle is a knob aft of the right.
On take off.
Fuel Flow is 25 GPH. Left. Read line is 17.5

I think you are going to tell me to get the throttle body set up correctly for a start.

Do you think the high fuel flow on take off has damage the diverter (spidy thing) on top of the engine? Or damaged the throttle body?

Posted 7/30/2023 - 6 months ago
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No MAP surge tells me WOT.

Not that it matters other than in discussion, but is this the left or right engine with the anomaly?

When you had the fuel control overhauled, did the installing agency set up the fuel system?

You called out FF on TO was 25; same on both engines?

Quite correct, sir; suggest starting with setting up the fuel systems per the M&O procedure; the spec for these engines fuel flow is 21.1-22.3, but common practice would be to set it a little higher, but I wouldn't go past 24. The red line you referenced on your fuel flow indicator is 17.5 psi (it is in fine print on the face of the indicator); your indicator is actually a pressure gauge that is calibrated in GPH, and 17.5 is the high end of the recommended nozzle pressure; again, a little higher helps the engine out.

The process of the fuel system(s) adjustment(s) not only brings the engines to best practice operating specification, but also is used as troubleshooting tool if something does not respond with the expected result, helping identify the problem. This should be checked yearly. Be sure to have your maintenance provide perform all the steps on both engines; partial power fuel flow is best set up if the idle fuel pressures are at the low end of the unmetered range with proper idle mixture adjustment, and the metered - nozzle - pressure at the high end of the range

On a twin, they are two independent engines that can be set in the recommended ranges, but if on opposite ends of the ranges, present different information to the pilot, so the process will take longer to make both engines harmonious with each other. This will also help align the throttle controls at the reduced MAP in the pattern.

The flow divider (spidy thing) is basically an on-off valve; the symptoms you describe do not point in that direction, although 17 years is a long time on a flexing diaphragm. Hi fuel flow should not have damaged the fuel control.

If you have digital engine monitoring, it may be helpful to download the information from that for us, but I would start where you thought I would suggest.

Mike
ABS Technical Advisor

Posted 7/30/2023 - 6 months ago
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Fixed!
I had the Throttle body set up and I changed the diaphragm in the Flow divider. Running smooth and now all cylinders are running at the same EGT.

I suspect that if one installs GAMI's and that diaphragm is old, it is a good idea to change it also.

Thank you.

Posted 9/13/2023 - 5 months ago
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Fuel flow fluctuation