Thread transferred May 2018
Engine Surging - 2200 Engine Engine J170D....1 year 6 months ago#402
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· Ross Clarke
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Hi Doug
I need some help troubleshooting an issue with Surging at full power with electric Pump switched off.
The Engine driven pump was replaced at scheduled maintenance 6 months ago, and I now have a situation as follows...
If electric pump is turned off during climb at full power, I get a big surge which rectifies immediately the pump is turned back on.
At cruise, in level flight with the electric pump off, all is good.
A ground static runup at almost full power produced surging with electric pump off, and smoothed out at about 2200 rpm.
So assuming the replaced engine driven pump is ok, can you advise steps to localise where the problem is?
Is there a recommended normal operating fuel flow measurement that can be done?
Its obvious that there is a fuel starvation issue at high power with the electric pump off.
Appreciate your comments Doug... Engine 150 hours tt since new
Regards Ross
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Engine Surging - 2200 Engine Engine J170D....1 year 6 months ago#407
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· Doug Smith
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Hi Ross,
Hm. Thats a bit of a novel one for me. By "surge" do you mean 10 or 20 rpm for a moment or two or more for longer? Do you have egt gauges?
Did anyone do anything with the carby at the time the pump was replaced? There are a few things in the carby that can do funny things with variations in fuel pressure - needle valve etc.
Regards,
Doug.
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Engine Surging - 2200 Engine Engine J170D....1 year 6 months ago#409
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· Ross Clarke
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Hi Doug. Thanks for reply, sorry I should have been more specific.
The surge is BIG.....like from full power to 1000 RPM which smooths out immediately the electric pump is turned on.
My Engine was used on the Jabiru Engine Maint course in March this year, and from memory, the Carby may have been dismantled and reinstalled for demo purposes but I would need to check with the Course Instructor.
Yes I have EGT and CHT Guage, and noticed recently that number 3 EGT was reading zero but put that down to a disconnected probe or loose wire.
Engine is smooth at cruise and CHT spread is within limits. EGTs on all but number 3 are normal.
I have ordered a new Fuel Pump which is currently in transit.,
Would you recommend Carby disconnection at this point?
Thanks Doug
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Engine Surging - 2200 Engine Engine J170D....1 year 6 months ago#411
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· Doug Smith
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Ah, so you're losing RPM. "Surge" had me thinking you were gaining it. That makes a little more sense!
Do you know if the EGT rises or lowers when you lose the RPM?
It does sound like the fuel flow to the carby isn't keeping up... Why was the fuel pump replaced previously? It may not be the pump - it's possible there's a partial crimp or similar in the line between the electric pump and the engine which allows fuel through when the electric pump is running but "sucks flat" when it's off. Dirty filter can have that effect sometimes...
For now, while the new pump is in transit, I'd suggest checking the carby float level, that the needle valve is sealing ok, and I'd have a look at the lines/filter and make sure there's nothing nasty lurking in that system.
Regards,
Doug.
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