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Merlin 160 - High idle?

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Merlin 160 - High idle?

Old 07-31-2005, 05:22 AM
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SAP_2000
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Default Merlin 160 - High idle?

My Merlin 160 seems to have a problem returning to idle (32K) after a flight.

On start up it ramps up to ~35K before settling down to 32K. and everything is fine. Problem is that after a 10 minute flight, it has a high idle rpm. (I'm guessing 40-45K) making even a draggy Eurosport difficult to slow down for landing. Once landed and taxied back after a minute or so, the idle seems to drop down to normal again.

One more thing: The engine shuts down every time I plug in the data terminal when running. If I start it up with the terminal connected it's all OK, even when I unplug it, but if I plug it back in with engine running it shuts down every time....

'Stability delay' is set at 100

Any ideas??
Old 07-31-2005, 03:19 PM
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Gaspar
 
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Default RE: Merlin 160 - High idle?

Hello Staale,

The High idle after a flight can be caused by the tank system. At startup the ecu calibrates the pump power for idle speed, and store this value as reference for all the run, but doing slow corrections. If at startup the pump have difficulty to pump fuel (due at tanks in series, for example) and at the end of the run it need less power for the idle (because it should suck the fuel from the last tank only), the result is that the idle will be a bit higher because the engine will receive more fuel with the same pump voltage. If during the flight you set idle often, the ecu self calibrates, but if all the flight is above idle, the ecu doesn't have the opportunity to correct the idle setting.

I'm interested in to see the measures stored by the ecu of your last 50 minutes of run to give you a much more accurate diagnostic. Please send me the file.

About the ecu resetting each time you plug the data terminal, I think that maybe is a problem in the connector of the data terminal.

Regards,

GAspar
Old 07-31-2005, 05:11 PM
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Default RE: Merlin 160 - High idle?

Hi again Gaspar!

I will send you the data i a few minutes.. Look closely at the second half of the last flight (cycle 34). You will see that the idle rpm starts out at ~45K on the landing and the slows very slowly down to 32K over a minute or so.

One thing I noticed was a little time before that, was that the rpm at one point dropped down to 28K. after that point the idle was high. Noticed that on the flight before that also (cycle 33). Maybe that rpm-drop below idle is what making the ECU adjusting the idle up???

Same e-mail address as before??
Old 08-02-2005, 02:31 AM
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Default RE: Merlin 160 - High idle?

Gaspar.

Did you get my e-mail with the 51 minutes of running history??
Old 08-02-2005, 12:15 PM
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Default RE: Merlin 160 - High idle?

Yes, just now, will come back to you by PM once analized.

Gaspar
Old 12-19-2008, 05:37 PM
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Default RE: Merlin 160 - High idle?

Hi Gaspar

If I understand correctely, the ECU self calibrates because the rpm sensor, but why does it take so long to calibrate?

Generally I only set the throtle to idle just before landing and at that time it is needed spool down to idle

Best regards

Nuno
Old 12-20-2008, 04:39 AM
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Default RE: Merlin 160 - High idle?

You understood incorrectly.

The pump power for idle rpm is calibrated at startup, and this value is used during the whole run. If "something" changes during the run that cause that this calibrated value is not longer valid, the ecu takes its time to calibrate again. The "something" could be a rough pump that after some time of running it becomes free and turn faster with same power, many tanks in series that make the work of the pump harder when all are full, etc, but this is always a sign of that something is not good in the installation. The ecu always default to a "high idle" rather than to a "low idle", if the engine rpm drop below idle the ecu reacts fast to recover, but in the contrary case it take its time.

Gaspar

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