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  #1  
Old 07-05-2011, 12:26 PM
BigJohn BigJohn is offline
 
Join Date: Nov 2008
Location: Gloversville, NY
Posts: 1,577
Default High fuel flow indication

Over the past month I made several cross-country flights, and tweaked the Dynon K factor as specified in the Dynon manual. Got it to the point where my fuel used (by Dynon) and fuel added (at the pump) were within .1 gallons. Pretty darn good, and was starting to feel confident in the Dynon readings.

Then - on my most recent trip, on climbout from Muskegon, MI, I got a high fuel flow alarm and a reading of over 10 GPH, up from the usual full throttle climb flow of 6.5 GPH. I leveled at cruise and the high reading continued. (I have the Dynon downloaded data file at the time of the incident.)I was clearly not really burning that much gas, as the engine continued to run fine and my actual consumption was normal for the leg. When I pulled the fuse for the electric boost pump, the flow returned to normal. This happened again on the next leg. Sudden onset, electric pump OFF back to normal, electric pump ON back to high rate. On my last leg all was normal.

I have yet to pull the top cowl and check the fuel pump for any signs of trouble - plan to do that tomorrow but would be surprised to see anything obvious. Is it possible the electric fuel pump is overpowering the engine driven pump and forcing extra fuel back through the return line? And why would this be happening intermittently? By any stretch of the imagination could this be a failure mode of the old style pump, and should I plan to replace it?

I have discussed this with Van's Support - they could not recall anything previous like this. They recommended I call Lockwood - spoke with their technician and got no help. I have just put messages out on both the Dynon and Rotax Owner's forums

Any advice/theories appreciated.
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  #2  
Old 07-05-2011, 01:31 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
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Default

No indications of a leak, right?

Dave
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  #3  
Old 07-05-2011, 02:02 PM
N223JH N223JH is offline
 
Join Date: Apr 2008
Location: Boerne, TX
Posts: 228
Default How about fuel pressure?

John, You have the download, right? Take a look at fuel pressure at the time of the high fuel flow incidents. As a matter of fact, scan the fuel pressure for the whole flight.

If your FP was dipping lower than normal, you may have the same syndrome I had...which was cured with a new engine-driven fuel pump.

Jim
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  #4  
Old 07-05-2011, 02:56 PM
Peterk Peterk is offline
 
Join Date: Mar 2008
Location: Texas
Posts: 1,378
Default

Quote:
Originally Posted by N223JH View Post
John, You have the download, right? Take a look at fuel pressure at the time of the high fuel flow incidents. As a matter of fact, scan the fuel pressure for the whole flight.

If your FP was dipping lower than normal, you may have the same syndrome I had...which was cured with a new engine-driven fuel pump.

Jim
John,
I think Jim is right. My does the same thing (with high pressure). The fuel pressure control mechanism is inside the mechanical fuel pump...it does not like dealing with two pumps. I put a temp on/off switch in (wired next to the electric one) with plans to buy a new fuel pump when they come out...which I understand Lockwood now has. Yes I know it shuts the avionics fans off...I just basically switch it off for a few seconds then back on and all works well for a little while. Hopefully the new pump will solve lots of problems.

Pete
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  #5  
Old 07-05-2011, 04:39 PM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,824
Default

Quote:
my actual consumption was normal for the leg.
John,
That means that fuel was not leaking nor was the engine using more than normal. That leaves two possibilities:
1. The flow sensor is going bad and is lying.
2. The flow sensor is telling the truth and the excess fuel is being returned to the tank.
Let's assume that fuel is being returned to the tank at a rate higher than normal. There are two possibilities for that:
1. The return line orifice has gotten bigger.
2. The fuel pressure has gone up.
It is unlikely that the size of the orifice has changed. So let's assume that the fuel pressure has gone up. The Dynon data log can be checked to confirm this scenario. If the fuel pressure has gone up, then a pressure relief valve (if built-in) internal to one of the pumps could have failed. Higher pressure causes higher flow rate.
Joe Gores
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  #6  
Old 07-05-2011, 05:57 PM
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MartySantic MartySantic is offline
 
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Location: Davenport, IA
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Default

John,

Sounds similar to what I experienced. Send me your Dynon download and I will take a look.
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  #7  
Old 07-05-2011, 07:22 PM
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RDOG RDOG is offline
 
Join Date: Apr 2009
Location: Propwash Airport (16X), Texas
Posts: 136
Angry beginning of the end

John,

Save yourself some trouble and get a replacement pump. This is the beginning of the end of that pump. I believe the pump is sucking air. These symptoms are the same if you drain the tank through the gas collator and as air is inducted the flow goes up while pressure goes down. Its insidious with this problem. As you trouble shoot it is on again and off again until the engine will only run on partial power then you got a problem. Good luck
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  #8  
Old 07-05-2011, 07:33 PM
BigJohn BigJohn is offline
 
Join Date: Nov 2008
Location: Gloversville, NY
Posts: 1,577
Default No change in fuel pressure.

All,

Thanks for all the responses. The funny thing is, there was no change in the pressure before, during, and after the incident.

Tomorrow I will pop the cowl off and check for stains at the weep hole.

Anybody know off hand if this type of pump failure has been covered under warrantee? And, what the procedure is to submit a claim?

Another question - I notice the new pump comes in two flavors, with and without the hoses. Which type would I need if I decided to bite the bullet and just order one?

John
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  #9  
Old 07-05-2011, 07:36 PM
JBPILOT JBPILOT is offline
 
Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,629
Default Hey BigJohn - -

About $180 for bare pump. About $575 with hoses. If warranty, and it should be for you, get the one with hoses. You have to pay for it up front, and wait for a couple months to get your money back. This assumes you can prove it is leaking.

John Bender
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  #10  
Old 07-05-2011, 08:13 PM
BigJohn BigJohn is offline
 
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Location: Gloversville, NY
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Default

Ouch! More tomorrow..............
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VAF paid through 10/2019.
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