REFLECTOR: Fuel Filters / Clogged Injectors

[jerry at jlbent.com]

It is important to understand that even a 40 micron filter (the one that is
part of the factory installation kit) did not prevent the clogging of
injectors on an IO540.

This is a bit off the filter thread (but related) and even farther off the
original thread so I have started a new and more appropriately titled one.

-----------------------

I have been remiss in documenting this so here goes:

We chased this problem for WAY too long.  The engine had been fine and
then it started running rough.  All I can figure is that the finer
fiberglass particles get through the "stock" filter and then when the
engine is shutdown the fuel evaporates and some resin is deposited and
carborizes in the bore of the injector.  A few engine runs later, the
injector is either completely blocked or blocked enough to cause the other
cylinders to be way rich.  If one injector is blocked then an IO540 will
run 16.6% rich and that is just about too rich to run.  This happens due to
the way fuel is distributed in the injector system.  For any RPM MP
setting, the air intake servo sends to the spyder the amount of fuel
appropriate for 6 cylinders.  This fuel is then distributed to the
injectors according to the flow characteristics of each line and injector
combination (this is where GAMI works to balance flow).  So, when one
injector is obstructed, the other 5 cylinders will be sharing what doesn't
go through the clogged injector.  This can be countered by leaning but the
best you can do is a rough engine with less than 83% power.  If you are in
the air, find an airport!  Believe that a 5 cylinder IO 540 is not
comfortable!

The general evidence for this is 5 cylinders with "wet" (black/sooty)
plugs and one that looks fine.  Since one cylinder is going LOP and the
rest are going ROP, the temps are not going to be a good diagnostic.

The fix is very simple.  Remove and clean all the injectors.  You will
probably find one that is obviously clogged (magnifying glass is a good
idea), any or all may be getting worse.  Be careful when reinstalling.
These injectors to distribution lines connectors are easly stripped.  The
directions are to bring them to "Finger Tight" and then 1/4 turn more.
This can be a bit tricky.  The distribution line must be properly straight
aligned with the injector.  The only way I know to do this is by feel.
When aligned you can screw the cap nut down until the distribution line
won't wiggle easily.  That's the magic "Finger Tight".

Many on this sight already know all of this and can correct and expand on
the information provided.  I know that this is an insidious problem and can
take months to diagnose on a fresh engine installation.  There are so many
variable that will provide the same behaviors and with a good filter that
look clean, it does not appear to be the problem.  I provide my experience
only as a amateur builder, not as a qualified A&P or especially a fuel
system expert.  It's all about the learning


Jerry Brainard
N202VB XLRG Building Slowly


  	-------Original Message-------
From: Dave Philipsen
Subject: Re: REFLECTOR: Fuel Consumption Performance
Sent: Aug 13 '09 5:48pm

HYTEC45 at aol.com wrote:
> In a message dated 8/13/2009 1:55:48 PM Pacific Daylight Time,
> [LINK: http://mbox.jlbent.com/compose.php?to=velocity@davebiz.com]
velocity at davebiz.com writes:
>
>     The sump/drain acts as a gascolator itself.
>
> True, however the cascolator has a 74 micron screen just in case any
> "floaters" are lurking.
> TEC
>
Good to know.

--
Dave Philipsen
Velocity STD FG
N83DP

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