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intermittent idle problem

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Wade

Joined: 16 May 2007
Posts: 16
Location: California

Posted: Fri Jun 15, 2007 3:28 pm Post subject: intermittent idle problem

Greetings experts...

  

 Recently purchased an RV6 (1994-98 build) with  a (H)IO-360 engine -- '95 vintage Airflow Performance (Bendix) injection  system/Performance Propeller cruise prop (wood w/ damper) and dual Electroair  ignition.   Performs beautifully... almost all the time.  I have  an intermittent idle issue.  It's not a typical rough idle, but when the  problem shows itself it's as if the ignition is turned off, then immediately  back on, i.e., smooth idle for several seconds, abrupt pause, smooth  idle...abrupt pause...etc.  Seems to occur more often with a hot engine,  though it's cropped up a few times on initial start-up.  The problem  has been consistent with the engine from day one... almost 300 tach  hours.  

  

 Troubleshooting so far:

     - replaced one electronic  ignition system with a mag... no change.

     -wrapped exhaust system and  installed heat shield between exhaust and fuel control... n/c.

     -checked all O-rings/connections  for possible air leak...n/c

     -installed 0.22 injector nozzles  to increase pressure downstream of flow divider... n/c.

  

 Other things that seem to have no  effect:

     -electric boost pump  on/off

     -direct air intake or  alternate

     -leaning

  

 One thing that sometimes clears the problem:   1800-2000 rpm for 30-45 seconds.

  

 Don, at Airflow Performance, is convinced I'm  vaporizing gas downstream of the flow divider, but so far no fix.  He  has recently set me a 'stiffer' spring for the flow divider.  I've  installed same and flown the aircraft a couple of times with no problems, but  I've often flown 2-3 times in a row with no problems, so the jury is still out  as to this being "the" fix.

  

 Anybody have a suggestion/theory/similar  experience?

  

 Dennis

 Virginia Beach

   [quote][b]

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glcasey(at)adelphia.net
Guest

Posted: Sat Jun 16, 2007 4:18 am Post subject: intermittent idle problem

It sounds very much like the "normal" hot fuel handling problem with  

the fuel system.  Vapor can form in several locations and I think Don  

has correctly diagnosed the problem - fuel vapor downstream of the  

fuel servo.  Symptom will be that after a hot start the engine will  

intermittently "quit" and if the speed is too low it might not  

recover.  Increasing engine speed will mask it.  Since there is no  

return line the vapor has to go through the injectors, but if it were  

downstream of the flow divider it is likely that only one cylinder  

would have the problem.  The most effective method of reducing the  

problem (a complete cure is probably not practical) is to insulate  

all the fuel lines in the engine compartment, paying special  

attention to the line between the servo and the flow divider.  For  

that reason I always use lines with the loose (red) firesleeve.  That  

makes a better insulator than the integral firesleeve lines you can  

buy.  If you have such a line in that location you can always add the  

loose sleeve over the other one.  The "stiffer" spring in the flow  

divider will hold a higher pressure in the system when the engine is  

shut off, tending to suppress vaporization - a good thing.



It shouldn't have that problem on a cold startup unless the fuel is  

leaking back through the system, which I suppose is possible if it is  

shut down for days or weeks.



Gary Casey

 	  Quote: 	
		  

 Greetings experts...



 Recently purchased an RV6 (1994-98 build) with a (H)IO-360 engine  

 -- '95

 vintage Airflow Performance (Bendix) injection system/Performance

 Propeller cruise prop (wood w/ damper) and dual Electroair ignition.

 Performs beautifully... almost all the time.  I have an intermittent

 idle issue.  It's not a typical rough idle, but when the problem shows

 itself it's as if the ignition is turned off, then immediately back  

 on,

 i.e., smooth idle for several seconds, abrupt pause, smooth

 idle...abrupt pause...etc.  Seems to occur more often with a hot  

 engine,

 though it's cropped up a few times on initial start-up.  The  

 problem has

 been consistent with the engine from day one... almost 300 tach hours.



 Troubleshooting so far:

     - replaced one electronic ignition system with a mag... no change.

     -wrapped exhaust system and installed heat shield between exhaust

 and fuel control... n/c.

     -checked all O-rings/connections for possible air leak...n/c

     -installed 0.22 injector nozzles to increase pressure  

 downstream of

 flow divider... n/c.



 Other things that seem to have no effect:

     -electric boost pump on/off

     -direct air intake or alternate

     -leaning



 One thing that sometimes clears the problem:  1800-2000 rpm for 30-45

 seconds.



 Don, at Airflow Performance, is convinced I'm vaporizing gas  

 downstream

 of the flow divider, but so far no fix.  He has recently set me a

 'stiffer' spring for the flow divider.  I've installed same and flown

 the aircraft a couple of times with no problems, but I've often flown

 2-3 times in a row with no problems, so the jury is still out as to  

 this

 being "the" fix.



 Anybody have a suggestion/theory/similar experience?



 Dennis

 Virginia Beach

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Wade

Joined: 16 May 2007
Posts: 16
Location: California

Posted: Mon Jun 18, 2007 7:17 am Post subject: intermittent idle problem

For Gary and Dave:



Thanks very much for your comments.   The red firesleeves were on all the

fuel lines when I bought the acft, but I wrapped the fuel filter

(which, interestingly, is forward of the firewall) for the reason you

suggest.  I've logged a couple of more flights with no symptoms -- no 

extended taxi ops, however.  A few symptom free flights and your 

experiences/recommendations have certainly boosted my confidence in the 

engine's reliability.  At the very least I know I don't have some weird 

'one-of-a-kind' gremlin.  Thanks again for your time and expertise.



Dennis

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