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  #51  
Old 01-03-2015, 05:44 PM
douglassmt douglassmt is offline
 
Join Date: Nov 2008
Location: Missoula, MT
Posts: 670
Default Mine

My plane has always needed the boost pump on in the climb if climbing to more than 8-9000 ft. If I turn off the boost pump before leveling off in cruise the fuel pressure will drop below 10 psi, triggering my alarm. Never had the engine stumble, just turn on the boost and fuel psi comes up to 20+, wait until level in cruise, turn off boost, psi stays at 20+. Mike Seager gave me the sop of keeping the boost pump on in the climb, I'm guessing for this reason.

My theory is the reduced cooling in climb plus the higher pump head (pitch up attitude) results in incipient vapor lock. I put a max reading temp strip on the mechanical fuel pump and I think it registered high at >190 IIRC. I may put a shroud and blast tube on it at annual, but I might not. Boost pump or slower climb rate resolves it. Seems to be worse at higher ambient temps.
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  #52  
Old 01-03-2015, 05:46 PM
jaybob jaybob is offline
 
Join Date: Nov 2006
Location: Colorado Springs
Posts: 25
Default Fuel Pump Issue

I had low PSI issues a while back using the original Tempest fuel pump. After doing all sorts of troubleshooting, I got fed up and swapped out to a new Lycoming pump... zero problems since. I don't know if the original pump had an issue or if using genuine Lyco was the solution. Regardless, low psi issues went away and life is good.

I've had a blast tube directed at the mechanical pump from day one, but no shroud. The fuel flow sensor is in the standard spot in the tunnel.

Cheers,
Jay
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  #53  
Old 01-03-2015, 06:10 PM
Ivan Kristensen's Avatar
Ivan Kristensen Ivan Kristensen is offline
 
Join Date: Mar 2008
Location: Guelph Ontario
Posts: 196
Default

Quote:
Originally Posted by douglassmt View Post
My plane has always needed the boost pump on in the climb if climbing to more than 8-9000 ft. If I turn off the boost pump before leveling off in cruise the fuel pressure will drop below 10 psi, triggering my alarm. Never had the engine stumble, just turn on the boost and fuel psi comes up to 20+, wait until level in cruise, turn off boost, psi stays at 20+. Mike Seager gave me the sop of keeping the boost pump on in the climb, I'm guessing for this reason.

My theory is the reduced cooling in climb plus the higher pump head (pitch up attitude) results in incipient vapor lock. I put a max reading temp strip on the mechanical fuel pump and I think it registered high at >190 IIRC. I may put a shroud and blast tube on it at annual, but I might not. Boost pump or slower climb rate resolves it. Seems to be worse at higher ambient temps.
This is very interesting and good information and that Mike Seager recommends to keep the boost pump on in the climb. it is good to know that 10psi is enough to feed the engine.
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  #54  
Old 01-03-2015, 06:16 PM
Lan Vinh Do's Avatar
Lan Vinh Do Lan Vinh Do is offline
 
Join Date: Nov 2007
Location: moncton NB
Posts: 208
Default same for me

Hi Ivan
I have the same issue. I keep the fuel pump until 2 or 3 min level. Never had engine trouble even if the pressure was down to 12psi. Always going back to 30 with the boost pump.
What i notice. It's more when it's hot.
The other thing is that i removed my left heat muff ( i placed aluminum shield 1/3 the circonference of the muffler ) and replace it with a fresh air that go from the front directly to the left heat ( cold) box. Inside my tunel, i have a Y and both front and back heat come from the right heat muff. I use the fresh air to cool under the panel

Since that day, i solve my hot tunel issue ( probably because fresh air wash the hot air that come from the right heat box when in the close position.

Second, i have less problem with hot start and my low fuel pressure alarm. With the heat generated by the heat muff, i just can imagine the heat that is discharge under the cowling when the heat box are closed and it's not so far from the fuel pump.

My Rv-7 had the same issue. So i don't think too much about it anymore.
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  #55  
Old 01-03-2015, 06:20 PM
N427EF N427EF is offline
 
Join Date: Oct 2005
Posts: 1,510
Default Interesting

I find it peculiar that some need the boost pump on and some don't.
It would be interesting to find out the differences in installations between those who do and those who don't need a boost pump for climb.

I usually turn the boost pump off just out of the traffic pattern after I change tanks to mogas.
Pressure usually drops 2 or 3 psi but recovers in about 5 seconds.

Blast tube and fuel pump shroud installed since new.
Engine compartment temp sensor installed on firewall just above the exhaust
pipes usually indicating around 150F.
Constant flow return line fuel system.
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  #56  
Old 01-03-2015, 06:56 PM
Jackm Jackm is offline
 
Join Date: Feb 2012
Location: Prosser,WA
Posts: 272
Default Drop in pressure in level flight

Ours will randomly drop in pressure in cruise. It will maintain 22 to 23 psi and every so often( once every 10 hours) will drop slowly to as low as 12 psi...at first it scared me and I would immediately switch on electric pump and it would rise immediately to 27 psi...then as it happened again I decided to watch it before switching elect pump on and it slowly drops to 12 psi and then starts climbing slowly back to 22 again. This only has happened in level flight because like Bryan stated Mike teaches to leave pump on in climb. We did install blast cooling shield because of Bob L experience. I am somewhat confident it is not wiring or sensor because of its responsiveness to switching on electric pump. Aerosport recommended new mechanical pump which we will replace at annual. It would be interesting to disect the mechanical pump when replacing but it may be hard to know the reason since it is so random.
We also have two fuel filters, one in each wing root and it will happen on either tank.
I think in our case the engine does start to slightly loose power ( going by sound and feel only) at 12 psi and fuel flow will drop about 1 gph during this event.
This is good discussion and would like feedback to solve for all of us.
And Bryan....it is NOT because we have a 430 instead of a 650
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  #57  
Old 01-03-2015, 07:05 PM
Jackm Jackm is offline
 
Join Date: Feb 2012
Location: Prosser,WA
Posts: 272
Default Drop in pressure in level flight

Ours will randomly drop in pressure in cruise. It will maintain 22 to 23 psi and every so often( once every 10 hours) will drop slowly to as low as 12 psi...at first it scared me and I would immediately switch on electric pump and it would rise immediately to 27 psi...then as it happened again I decided to watch it before switching elect pump on and it slowly drops to 12 psi and then starts climbing slowly back to 22 again. This only has happened in level flight because like Bryan stated Mike teaches to leave pump on in climb. We did install blast cooling shield because of Bob L experience. I am somewhat confident it is not wiring or sensor because of its responsiveness to switching on electric pump. Aerosport recommended new mechanical pump which we will replace at annual. It would be interesting to disect the mechanical pump when replacing but it may be hard to know the reason since it is so random.
We also have two fuel filters, one in each wing root and it will happen on either tank.
I think in our case the engine does start to slightly loose power ( going by sound and feel only) at 12 psi and fuel flow will drop about 1 gph during this event.
This is good discussion and would like feedback to solve for all of us.
And Bryan....it is NOT because we have a 430 instead of a 650
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  #58  
Old 01-03-2015, 08:49 PM
Wayne Gillispie Wayne Gillispie is offline
 
Join Date: Apr 2009
Location: USA
Posts: 1,494
Default

I have a temp labels on my alt, mech pump and magnetos. Max temps reached on alt surface facing #1 exh pipe= 300F with no issues so far. Mech fp max= 225F with no shroud. Magneto max= 200F. No blast tubes. Min fuel pressure alarm set at 15 psi. Has alarmed on a couple of hot climbs. I have ff transducer in tunnel which does restrict flow. Turning on boost pump and leveling off cured it. Never ran rough. I did order the upgraded SS fuel pres transducer from GRT to replace the automotive quality VDO sender. Have not installed yet. I also have cowl outlet temp switch that has an adj opening temp. It is set at 230F and has only alarmed once at 16,500' cruise due to thin air, near gross, near aft limit with 6 degree pitch angle. Normally 3 deg at 12,500' cruise.
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  #59  
Old 01-04-2015, 03:44 AM
RV10inOz's Avatar
RV10inOz RV10inOz is offline
 
Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,116
Default

This is not unusual.

Hot fuel, sucking uphill in the climb and lowering outside pressure. Hot pumps too.

Bonanzas are the same!

Leave the pump on and until 5-10after TOC.

Installing the pump cooling shroud helps.

You are not abnormal if that helps.
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  #60  
Old 01-04-2015, 04:59 AM
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rleffler rleffler is offline
 
Join Date: Jun 2006
Location: Delaware, OH (KDLZ)
Posts: 3,896
Default

I've already shared this with Ivan.

When I replaced my pump over a year ago, I installed the shroud at the same time. This means I'll never know the true root cause of my issue.

I can state that I can now take off with the electric pump off and the mechanical pump has no problem maintaining proper fuel pressure on the climb during the summer temps.

I suspect that's due to the shroud, but I don't have the data to prove that.

Bob
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