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Pre Flight Problems

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rveighta(at)earthlink.net
Guest

Posted: Wed May 21, 2008 4:44 pm Post subject: Pre Flight Problems

Listers, I'm hoping to make the first flight of my RV-8 in the next few days, but I have a couple of problems I need to sort out first.



   - With the Batt & Avionics Master on, the manifold pressure needle pegs when the radio xmit button is 

     pressed. Any ideas about what could be causing this?



   - With the Batt Master On, before engine start, the fuel pressure gauge is at zero; as soon as I hit the

     boost pump it climbs to around 30psi and stays there during engine run (with the boost pump turned off)

     What is normal fuel pressure for  an engine with carburetor with the engine running? (Can't find this 

     in my engine manual). 



Thanks,



Walt Shipley   RV-8a Flying,  RV-8 soon to be flying



Do not archive

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rnewman(at)tcwtech.com
Guest

Posted: Wed May 21, 2008 5:20 pm Post subject: Pre Flight Problems

Walt,   It sound like your MP gauge and or sender are sensitive to the 

radiated or conducted fields from your comm transmitter.   Perhaps a poor 

ground connection on the sender or the gauge.  Another possibility is a poor 

shield connection on the antenna wire between the radio and the antenna.   I 

had significant trouble with some BNC connectors where the shield was making 

intermittent contact to the outer shell of the connector.   This caused all 

kinds of problems.



          Regarding the fuel pressure,   Lycoming fuel pumps on carb type 

engines generally run in the 4-6 psi range.   30psi sounds like the fuel 

pump is the type intended for fuel injected engines that run in that higher 

range.



           When you turn on the boost pump only before starting the engine 

to you get a reading closer to 5 psi?



-Bob Newman

rv-10 40176

Glastar N99RN

www.tcwtech.com





---

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khorton01(at)rogers.com
Guest

Posted: Wed May 21, 2008 5:49 pm Post subject: Pre Flight Problems

On 21 May 2008, at 20:40, rveighta wrote:



 	  Quote: 	
		   



 Listers, I'm hoping to make the first flight of my RV-8 in the next  

 few days, but I have a couple of problems I need to sort out first.



    - With the Batt & Avionics Master on, the manifold pressure  

 needle pegs when the radio xmit button is

      pressed. Any ideas about what could be causing this?



Which MP gauge do you have?
	




This appears to be a relatively common complaint with Van's MP  

gauge.  It seems that it picks up radio frequency energy.  I haven't  

seen a solution, other than not looking at the MP gauge when  

transmitting.



 	  Quote: 	
		      - With the Batt Master On, before engine start, the fuel  

 pressure gauge is at zero; as soon as I hit the

      boost pump it climbs to around 30psi and stays there during  

 engine run (with the boost pump turned off)

      What is normal fuel pressure for  an engine with carburetor  

 with the engine running? (Can't find this

      in my engine manual).


	


Where in the fuel system are you measuring fuel pressure?



If you have an O-360, with a Facet (Marvel Schebler) MA-4 or HA-6  

series carb, the fuel pressure at the inlet to the carb should be  

between 0.5 and 8 psi.  This info is from engine Type Certificate  

Data Sheet E-286, available on the FAA web site.

 	  Quote: 	
		  


	


--

Kevin Horton

RV-8 (FInal Assembly)

Ottawa, Canada

http://www.kilohotel.com/rv8

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Gary.A.Sobek

Joined: 09 Jan 2006
Posts: 217
Location: SoCAL USA

Posted: Wed May 21, 2008 5:54 pm Post subject: Pre Flight Problems

Going from memory, the minimum fuel pressure for a carb is 0.5 psi.  (1/2 psi)  Depending on the transducer, it may have a difficult time ready as low as 0.5 psi.  Not sure what fuel pressure instrument you have. Is it programmable and possible that it has an incorrect calibration factor?  It is possible that you have a bad gauge or a bad transducer. You will need to know about the meter movement to trouble shoot it.



Saw a Draganfly with VW engine that had the same problem with all its engine instruments as you do with MAP. The problem there was a BAD ground scheme.  Ground loop and high resistance.  The builder added a ground just for the transducer and his problem when away.  Cannot say that is your problem but poor grounds are the source of a lot of instrument problems.



Gary A. Sobek

"My Sanity" RV-6 N157GS O-320 Hartzell,

2,096 + Flying Hours So. CA, USA



[quote] From: rnewman(at)tcwtech.com

 To: rv-list(at)matronics.com

 Subject: Re: Pre Flight Problems

 Date: Wed, 21 May 2008 21:17:12 -0400



 



 Walt, It sound like your MP gauge and or sender are sensitive to the

 radiated or conducted fields from your comm transmitter. Perhaps a poor

 ground connection on the sender or the gauge. Another possibility is a poor

 shield connection on the antenna wire between the radio and the antenna. I

 had significant trouble with some BNC connectors where the shield was making

 intermittent contact to the outer shell of the connector. This caused all

 kinds of problems.



 Regarding the fuel pressure, Lycoming fuel pumps on carb type

 engines generally run in the 4-6 psi range. 30psi sounds like the fuel

 pump is the type intended for fuel injected engines that run in that higher

 range.



 When you turn on the boost pump only before starting the engine

 to you get a reading closer to 5 psi?



 -Bob Newman

 rv-10 40176

 Glastar N99RN

 www.tcwtech.com





 ---

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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