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intermittent idle problem

 
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Wade



Joined: 16 May 2007
Posts: 16
Location: California

PostPosted: Fri Jun 15, 2007 3:28 pm    Post subject: intermittent idle problem Reply with 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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glcasey(at)adelphia.net
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PostPosted: Sat Jun 16, 2007 4:18 am    Post subject: intermittent idle problem Reply with quote

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

PostPosted: Mon Jun 18, 2007 7:17 am    Post subject: intermittent idle problem Reply with quote

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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