Matronics Email Lists :: View topic - Two Fuel pumps Z-19RB

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

Two Fuel pumps Z-19RB

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

Sam

Joined: 18 May 2008
Posts: 135

Posted: Sun Jun 15, 2008 8:22 am Post subject: Two Fuel pumps Z-19RB

All,



I am looking for a better way to handle switching for my fuel injection fuel pumps.  I have uploaded the diagram here:

http://www.mistakeproofing.net/transfer/N202SH_POWER_DISTRIBUTION_06.pdf  Look in the lower portion of the drawing.

 I am using the RWS fuel/ignition controller which has the ability to receive power from two sources, which should fit well with Z-19.

However, I have added a backup fuel pump.  I have a selector switch that determines which system supplies the fuel pumps.  Then, I have added a switch that will allow me to run either pump, but not both.

 

The problem is, I have to feed each pump through two switches, doubling my chance of failure.



Any suggestions?



Thanks.



Sam Hoskins

Quickie Q-200 EFI

  [quote][b]

_________________
Sam Hoskins
www.samhoskins.blogspot.com

klehman(at)albedo.net
Guest

Posted: Sun Jun 15, 2008 9:29 am Post subject: Two Fuel pumps Z-19RB

Sam

I run an oem subaru EFI as my primary. I am not concerned if I happen to 

  have both fuel pumps on together. With both of my pumps on, the 

pressure goes up 2 or 3 psi. The fuel flow change is minuscule 

(proportional to the square root of the fuel pressure). Nominal is 

around 36 psi above MAP. Actually my engine continues to run if I double 

the normal fuel flow. My hazy memory is that the oem pumps draw about 4 

amps or so each so that is not a big deal either.



I chose to not give either computer the ability to control the second 

fuel pump. Some guys like to retain auto shutdown of both pumps in the 

event of a crash but my second pump is not normally on in flight. I 

preferred to have no switches or wiring that is common to both pumps 

which also simplifies things.



Ken



Sam Hoskins wrote:

 	  Quote: 	
		   All,

 

 I am looking for a better way to handle switching for my fuel injection 

 fuel pumps.  I have uploaded the diagram here:

 http://www.mistakeproofing.net/transfer/N202SH_POWER_DISTRIBUTION_06.pdf  

 Look in the lower portion of the drawing.

 I am using the RWS fuel/ignition controller which has the ability to 

 receive power from two sources, which should fit well with Z-19.

 However, I have added a backup fuel pump.  I have a selector switch that 

 determines which system supplies the fuel pumps.  Then, I have added a 

 switch that will allow me to run either pump, but not both.

 

 The problem is, I have to feed each pump through two switches, doubling 

 my chance of failure.

 

 Any suggestions?

 

 Thanks.

 

 Sam Hoskins

 Quickie Q-200 EFI

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Jun 16, 2008 4:54 am Post subject: Two Fuel pumps Z-19RB

Sam, 

  

Why are you using a double pole  switch for "System B Engine Secondary"  ECU instead of a single pole switch? 

  

Suggestion for Ignition Coil +12V  Supply: connect switch terminals 1 & 4 together and terminals 3 & 6  together for redundancy. 

  

Would it hurt anything to have  two pumps running at once?  It would  greatly simplify the circuit to have one switch for each pump, with each switch  having 3 positions: source A, OFF, source B.  It would be up to the pilot to make sure  that only one pump in turned on at a time. 

  

If you absolutely have to prevent  both pumps from running at once, let me know and I will draw a circuit using  either 4 switches or else 2 switches plus diodes. 

<?xml:namespace prefix = o ns =  "urn:schemas-microsoft-com:office:office" />  

Joe

   [quote][b]

_________________
Joe Gores

Sam

Joined: 18 May 2008
Posts: 135

Posted: Mon Jun 16, 2008 5:19 am Post subject: Two Fuel pumps Z-19RB

I think it might be better to only have one fuel pump at a time, to prevent overloading the pressure regulator.  I don't know how much flow the P.R. can handle, since I have not yet powered up the system.  If the regulator can handle two pumps, then no problem.  However, if it can't, then running two pumps may adversely affect the mixture. 

 

I recently saw an accident report involving a Lancair IV where it is speculated that two pumps were running at once and the engine lost power because of an excessively rich condition.



Anyway, that's my reasoning.

 

Sam Hoskins

 Quickie Blog

 Quickie Website



On Mon, Jun 16, 2008 at 7:52 AM, Joe <fran5sew(at)banyanol.com> wrote:

 	  Quote: 	
		           

Sam, 

  

Why are you using a double pole  switch for "System B Engine Secondary"  ECU instead of a single pole switch? 

  

Suggestion for Ignition Coil +12V  Supply: connect switch terminals 1 & 4 together and terminals 3 & 6  together for redundancy. 

  

Would it hurt anything to have  two pumps running at once?  It would  greatly simplify the circuit to have one switch for each pump, with each switch  having 3 positions: source A, OFF, source B.  It would be up to the pilot to make sure  that only one pump in turned on at a time. 

  

If you absolutely have to prevent  both pumps from running at once, let me know and I will draw a circuit using  either 4 switches or else 2 switches plus diodes. 

  

Joe

    	  Quote: 	
		  [b]

[/b] 	




	




  [quote][b]

_________________
Sam Hoskins
www.samhoskins.blogspot.com

jon(at)finleyweb.net
Guest

Posted: Mon Jun 16, 2008 6:44 am Post subject: Two Fuel pumps Z-19RB

Sam,

  

 I'm running the RWS system on my Subaru EJ-22 and run both pumps for takeoff, landing, and NOE missions (Nap-Of-the-Earth).  I can't even guess how your O-200, pumps, and regulator will react but mine all work very well together with about a 2-3 psi pressure rise when both are on.  This makes no noticeable difference to the mixture.

  

 Jon

--

jon(at)finleyweb.net
Guest

Posted: Mon Jun 16, 2008 6:47 am Post subject: Two Fuel pumps Z-19RB

Also, I run my primary ECU power and primary EFI pump from a single 'primary' switch (and a relay) which is on the battery bus.  The aux EFI pump is on it's own switch.

  

 Jon

--

Sam

Joined: 18 May 2008
Posts: 135

Posted: Mon Jun 16, 2008 3:48 pm Post subject: Two Fuel pumps Z-19RB

Jon,



What fuel pumps and fuel regulator are you using?  I want to make sure we are comparing apples to apples.  I have Walbro pumps and an Airmotive regulator.



Sam



On Mon, Jun 16, 2008 at 9:41 AM,  <jon(at)finleyweb.net (jon(at)finleyweb.net)> wrote:

[quote] Sam,

  

 I'm running the RWS system on my Subaru EJ-22 and run both pumps for takeoff, landing, and NOE missions (Nap-Of-the-Earth).  I can't even guess how your O-200, pumps, and regulator will react but mine all work very well together with about a 2-3 psi pressure rise when both are on.  This makes no noticeable difference to the mixture.

   

 Jon

--

_________________
Sam Hoskins
www.samhoskins.blogspot.com

jon(at)finleyweb.net
Guest

Posted: Mon Jun 16, 2008 4:32 pm Post subject: Two Fuel pumps Z-19RB

Ya,  definitely not the same setup that I have.  I am using the stock 1990-1994  Subaru EJ-22 fuel pressure regulator and two pumps from the 1992 Subaru  Loyale.

  

 I  think it would be worth it to wire them up on the bench with a pressure  regulator hooked up and run a test.  We have such a large header tank that  I don't think heat build up in the fuel is an issue but, as you said, the  inability for the regulator to maintain the correct pressure is an  issue.

  

 Jon

  

 [quote]   --

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Jun 16, 2008 5:58 pm Post subject: Two Fuel pumps Z-19RB

Sam,

 How about the attached circuit?  Four fuses are necessary in case a  pump shorts out and blows two of them.  The switch is still a single  failure point.  It would be better to tolerate two pumps running at  once.  It would seem that regulators should be available to handle the flow  rate of two pumps.  If you do not want the voltage drop of diodes, two of  SPDT switches could be used instead of diodes.  The more complicated the  circuit, the greater the chance of something going wrong.

 Joe

Fuel_Pumps.jpg

Description:

Filesize:

220.99 KB

Viewed:

225 Time(s)

_________________
Joe Gores

sshook(at)cox.net
Guest

Posted: Wed Jun 18, 2008 10:44 am Post subject: Two Fuel pumps Z-19RB

Correct me if I am wrong here, but this is my understanding of a Fuel Injected systems such as Subaru’s.   

   

On a continuous loop system such as the Subaru FI system, doesn’t the EFI computer control the mixture (rich/lean) and not the fuel pumps?  The fuel system pumps gallons of fuel through in a matter of minutes and the EFI system allows only a small portion of that fuel to be released by the injectors into the combustion chamber.  

   

Having both pumps on during takeoff, landing, and other low altitude maneuvers is only good measure in case of a failure on the single pump.    

                                

 Scott R. Shook 

 RV-7A (Building) 

 N696JS (Reserved)   

        

  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Sam Hoskins

 Sent: Monday, 16 June, 2008 06:13

 To: aeroelectric-list(at)matronics.com

 Subject: Re: AeroElectric-List: Two Fuel pumps Z-19RB  

  

   

I think it might be better to only have one fuel pump at a time, to prevent overloading the pressure regulator.  I don't know how much flow the P.R. can handle, since I have not yet powered up the system.  If the regulator can handle two pumps, then no problem.  However, if it can't, then running two pumps may adversely affect the mixture. 

 

 I recently saw an accident report involving a Lancair IV where it is speculated that two pumps were running at once and the engine lost power because of an excessively rich condition.

 

 Anyway, that's my reasoning.

 

 Sam Hoskins

 Quickie Blog

 Quickie Website    

On Mon, Jun 16, 2008 at 7:52 AM, Joe <fran5sew(at)banyanol.com> wrote:      

Sam,  

   

Why are you using a double pole switch for "System B Engine Secondary"  ECU instead of a single pole switch?  

   

Suggestion for Ignition Coil +12V Supply: connect switch terminals 1 & 4 together and terminals 3 & 6 together for redundancy.  

   

Would it hurt anything to have two pumps running at once?  It would greatly simplify the circuit to have one switch for each pump, with each switch having 3 positions: source A, OFF, source B.  It would be up to the pilot to make sure that only one pump in turned on at a time.  

   

If you absolutely have to prevent both pumps from running at once, let me know and I will draw a circuit using either 4 switches or else 2 switches plus diodes.  

   

Joe  

   	  Quote: 	
		     	


  

  

  

    	  Quote: 	
		     	
0 	  Quote: 	
		   	
1 	  Quote: 	
		   	
2 	  Quote: 	
		   	
3 	  Quote: 	
		   	
4 	  Quote: 	
		   	
5 	  Quote: 	
		   	
6 	  Quote: 	
		   	
7 	  Quote: 	
		   	
8 	  Quote: 	
		   	
9 	  Quote: 	
		   	
0 	  Quote: 	
		   	
1 	  Quote: 	
		   	
2

       [quote][b]

jon(at)finleyweb.net
Guest

Posted: Wed Jun 18, 2008 12:40 pm Post subject: Two Fuel pumps Z-19RB

Hi Scott - Good Question but a long answer... 

  

 With an OEM EFI system (i.e. Subaru), there are two modes to consider - Open and Closed loop.  In Closed loop, the oxygen sensor output is being referenced by the ECU and the mixture is adjusted to obtain the optimal setting (stoichiometric).  In Open loop, lookup table data values are used to set the mixture (based on RPM, atmospheric pressure, and ??? (I can't remember but it seems like there is more..)).  In both cases, the mixture is varied by the amount of time the injectors are open (pulse width).  In most all modes of flight, the OEM ECU is in Open loop mode.  For example; the EJ-22 Legacy ECU goes into Open loop mode at about 3000 rpm (if memory serves). A number of people running the OEM system were varying fuel pressure to adjust the mixture in flight.

  

 The RWS system (EC2) does not use an oxygen sensor - rather only a set of lookup tables. These values are very easy to set by the operator (in flight or on the ground) plus a mixture "dial" is also provided to set the mixture during atypical situations (i.e. idle when very cold (richen), long-hot climb (richen for cooling), etc...).

  

 In the case of the OEM Open Loop and all the time for the RWS system, increasing the fuel pressure will result in more fuel being injected for the given injector pulse. Higher pressure - richer mixture, lower pressure - leaner mixture.  So, going back to the conversation; when fuel pump one is running, I see about 36 psi. Turning on pump two increases the presure by about 3psi which affects the mixture (richens) but it is by such a small percentage that it is really not noticeable (at least not on the air/fuel ratio guage that I use).

  

 The issue that I believe Sam is worried about is his fuel pressure regulator being unable to 'bypass' enough fuel when both pumps are on resulting in the pressure climbing and the mixture getting richer and richer.

  

 Jon



--

Display posts from previous:

	Matronics Email Lists Forum Index -> AeroElectric-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum