Dukes Fuel Pump Drip

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RMarkSampson
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Dukes Fuel Pump Drip

Postby RMarkSampson » Fri Jan 09, 2015 12:57 am

My DA-20-C1 recently started to have a fuel drip from the vent hose coming out of the bottom of the 2-speed Dukes Fuel Pump. Doing some research on the web, it looks like this fuel pump tends to wear out around 400 hours (mine made it 600 hours - although I now suspect that the low pressure side of the pump has not been contributing to my fuel pressure for some time). Looks like two options for me to replace/refurb the pump. One is going with the single-source OEM-appointed repair company (QAA) to purchase a very overpriced exchange/replacement at $1,295. The other option is going with a company named Aeromotors, LLC up in WI that reportably has all the certs and experience to rebuild my current pump. Another blog favorably mentioned their work, they have an add on Trade-a-Plane, and an informative website. Their price is $500 plus $20 shipping which is much better than the OEM-directed route. Has anyone gone this route to service their Dukes fuel pump? I would certainly like to hear their opinion/recommendation.
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Re: Dukes Fuel Pump Drip

Postby keithPTC » Sun Jan 25, 2015 5:59 pm

Mark, what route did you end up going to repair the drip on the Dukes pump?
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Re: Dukes Fuel Pump Drip

Postby RMarkSampson » Sun Jan 25, 2015 7:50 pm

Keith,
I went with Aeromoters LLC ( http://www.aeromotorsllc.com/aeromotorsllc/ ). I did Google-map their address as I wanted to see their building and have an idea of what type of LLC I was dealing with -- they looked reputable and were not a "garage business." So I sent them the pump and a check for the $520. They sent me the return UPS tracking number last week. It is scheduled to arrive tomorrow, exactly two weeks after I ground-UPS'ed it to them (on a Monday - and they got it on that Thursday). You can certainly speed up the process by going with a faster shipping option but I was not concerned with an immediate turn-around. So the jury is still out but so far everything seems good to go. They did cash the check the day the pump got to them. I'll update this post once the pump is back in and fly a few hours.
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Re: Dukes Fuel Pump Drip

Postby keithPTC » Sun Jan 25, 2015 7:53 pm

Thanks for the followup!
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Re: Dukes Fuel Pump Drip

Postby RMarkSampson » Sat Feb 28, 2015 7:29 pm

Just to fully close the loop on this issue. The pump is back in and working perfectly. Very pleased with the result and I certainly recommend Aeromoters LLC vice the OEM solution. Before I was hard pressed to see a fuel pump pressure rise on my EMS when it was on the low pump setting. Now I can see a positive rise in the fuel pressure when the pump is switched on the low setting giving me full confidence that the pump is operating to specification.
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Re: Dukes Fuel Pump Drip

Postby RMarkSampson » Tue May 12, 2015 2:18 am

All,
This is an important final step in the saga of dealing with your Duke’s Fuel Pump. CONTINENTAL MOTORS AIRCRAFT ENGINE SERVICE INFORMATION DIRECTIVE SID97-3F. SID97-3F is compulsory at Engine Installation, 100 hour/Annual Inspection, fuel system component replacement or as required if operation is not within specifications – and applies to most CMI continuous flow fuel injected engine models (i.e. the IO-240B in my DA-20).

Subject: CONTINENTAL MOTORS, INC. (CMI) CONTINUOUS FLOW FUEL INJECTION SYSTEMS ADJUSTMENT SPECIFICATIONS AND INSTRUCTIONS. http://www.tcmlink.com/pdf2/SID97-3F.pdf

There are a few things required to complete this SID. My local FBO did not have the tools to test so I started working this issue on my own. The SID reference a Model 20 ATM-C Porta Test Unit P/N 630045-20 but the $5,000 price tag quickly made that option a non-starter. However, the SID also states that "calibrated pressure gauges may be purchased from various suppliers such as: Davis Instruments" – this is the route I am taking. There are two gauges to purchase. The first one is a calibrated 0-60 PSI gauge, graduated in 1 PSI increments. This gauge will be used for unmetered fuel pressure measurement. The second gauge is a calibrated 0-30 PSI gauge, graduated in .2 PSI (maximum) increments, to be used for metered fuel pressure measurements and verification of aircraft fuel flow indications on normally aspirated engines. I could not find one in .2 increments but was able to get it in .5 increments which should be acceptable for the test. Each gauge was about $30, but it was about $200 to have them both calibrated. Also required are Two (2) P/N MS51523-B4 swivel tee to connect the gauges into the fuel system which I picked up for ~$56. A trip to the local hose supply store got me everything I needed to put together the fuel testing system - 2x 10' hose, 2x shut-off valves, 2x bleed valves, 4x end-fittings for the hose. See attached picture.

All told, I’m in for about $500, but I now have the ability to test my fuel system at my annual or anytime the fuel system is touched – or if I suspect an issue with the electric fuel pump. With all the trials and troubles of the electrical fuel pump experienced by other Diamond owners (both DA-20 and DA-40s) - I consider it money well spent.
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Fuel Test Gauges Built for SID97-3F.jpg
Pic of my fuel test system - 10 feet of hose each to keep me away from the whirling blade of death during testing.
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Re: Dukes Fuel Pump Drip

Postby keithPTC » Tue May 12, 2015 9:30 am

RMarkSampson wrote:All,
This is an important final step in the saga of dealing with your Duke’s Fuel Pump. CONTINENTAL MOTORS AIRCRAFT ENGINE SERVICE INFORMATION DIRECTIVE SID97-3F. SID97-3F is compulsory at Engine Installation, 100 hour/Annual Inspection, fuel system component replacement or as required if operation is not within specifications – and applies to most CMI continuous flow fuel injected engine models (i.e. the IO-240B in my DA-20).


Mark,

Thanks for sharing this! Very helpful tips for building an alternative to the Porta-Test.

After reading SID97-3F, I would suggest that compliance with this procedure is not required when the Dukes pump is changed as this procedure only checks the pressure of the engine driven fuel pump. The Dukes boost pump is required to be kept "off" while performing the procedure.

Notice that Table 3 on page-12 of SID97-3F specifies that IO-240-A,B engines "SEE Maintenance Manual M-6." Good news here. Manual M-6 changes the inspection requirements in our favor. Page 6-15 of Manual M-6 specifies that the procedure is only required, "after replacement of fuel injection system components, such as the fuel pump, fuel manifold valve, or fuel injectors." Again, it's referring to the engine driven fuel pump, and there's nothing in there anymore about annuals or 100-hour inspections. However, Manual M-6 does require that the 0-30 gauge be graduated in 0.1 psi (maximum) instead of the .2 psi as specified in SID97-3F.

Attached are the relevant pages from the Continental M-6 Manual showing the procedure. Notations are mine.

Thoughts?
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Continental M-6 Fuel Check.pdf
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RMarkSampson
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Re: Dukes Fuel Pump Drip

Postby RMarkSampson » Tue May 12, 2015 7:34 pm

Keith,
Good feedback - here is where I am at. The Dukes fuel pump makes a dramatic impact to fuel system pressure and it is used during the two most critical phases of flight - takeoff and landing. So why would I not record fuel pressures with and without the Duke's pump turned on? Continental's M6 and SID will not focus on the electric fuel pump as it is not their equipment - but Diamond (and Diamond owners) should certainly need to understand how the boost pump interacts with the engine.

First, a weak or broken boost pump like many of us have experienced will not provide the necessary backup to the engine driven fuel pump. This condition may not be readily apparent until the main engine fuel pump actually fails. When I reinstalled the boost pump in my DA-20, the boost pump's low pressure setting now showed a positive rise before starting the engine - which I had not seen prior to the boost pump rebuild. In my mind, in addition to the M6/SID procedure, annual testing of the boost pump fuel pressures without the engine running seems to be a prudent fuel system maintenance check.

Secondly, I also found the low pressure setting now significantly impacted the richness of the fuel mixture - to the point that the engine will not shut-down at full Idle Cutoff if the boost pump is left on. Just like when you prime the engine with the boost pump using the high pressure setting, the boost pump now has enough pressure at the low pressure setting to inject fuel directly into the cylinders. Another change I noted was my recently rebuilt boost pump now makes the engine run rougher during ground idle ops. I frequently now turn off the boost pump during taxi - and the engine runs smoother and I see a rise in RPM. I then turn the boost pump back on during my run-up. This has also led to a new concern of mine that an excessively rich mixture caused by the boost pump may limit takeoff power - especially if I fly to a high-altitude airport.

So I see overlapping issues. Beyond just complying with the M6 or SID, I am interested in knowing how my "total fuel system" is operating. All this means is I need to research further - starting with asking Diamond for their assessment on how to best test both the engine-driven fuel pump and the boost pump. Ultimately, I believe knowing the nominal fuel pressures in all configurations used during flight is best.

OBTW, I actually have not tested yet so I'll post what I figure out when I test.
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Re: Dukes Fuel Pump Drip

Postby keithPTC » Tue May 12, 2015 10:14 pm

Have you considered sending the pump back to Aeromotors to confirm that their pump overhaul was done to proper specs?
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Re: Dukes Fuel Pump Drip

Postby RMarkSampson » Tue May 12, 2015 11:17 pm

I believe the boost pump is operating to spec. I have a Vision Microsystems Engine Monitoring System in my DA-20 and can read the fuel pressure directly from its display. If I just watch the display after turning on the boost pump, before I start the engine it reports 3 psi - which is the exact spec for the low speed setting of the Dukes pump stamped on the side of the pump. I'll confirm this with the fuel test equipment setup I now have to use - but still believe that Aeromotors did an excellent rebuild. I think the differences I am seeing in engine operation can be attributed to a fully functional boost pump - and not the other way around.

A good read has been an article Continuous Flow Fuel Injection Systems by Randy Knuteson. See the chapter on "Setting up the System - Is 'Fine-Tuning' Required?" - he advocates for the fuel pressure testing. His last paragraph restates the SID - "Continental encourages an “operational verification” any time an engine is installed, a 100 hr. or annual is performed, or whenever a fuel component is replaced or adjusted. This may seem “excessive,” but it assures of a smooth running engine to TBO." My FAA-cert mechanic agrees with Randy - and he is not motivated by $$ as he only works for fun, flight hours and all the pancakes we can eat so long as we fly to get them.

http://www.kellyaerospace.com/articles/ ... usFlow.pdf

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