[Vwdiesel] Solenoid valve on turbo-line test *RESULTS*

[LBaird119 at aol.com]

> I really have to win one of these auctions for a Bentley book on Ebay, <g>
or
> have someone explain to me how this whole system works.

  Turbo end of things.
  On a NA (Naturally Aspirated) engine.  The suction of the cylinders pulls
the
air into the cylinder.  It then compresses to a high temperature, the fuel is
injected directly into the combustion prechamber.  It ignites pushes the
piston down, then the exhaust stroke and so forth.
  Add a turbo and the exhaust runs a turbine.  A direct drive shaft from the
turbine drives a compressor wheel.  This wheel makes positive pressure
in the intake manifold so when the intake valve opens, air isn't just sucked
into the cylinder, it's forced in as well.  This gives you more oxygen
available
for combustion.  The two keep compounding on each other to make the turbo
spin faster and faster until the intake pressure reaches the preset maximum
of about 10 psi.  At that point a wastegate opens on the exhaust side.  This
is a bypass around the turbine so that it will not spin any faster than it
presently is.
  Compressing air makes heat, especially when you use a fan type of
compressor rather than a displacement type.  On these engines once
you reach about 6psi, your intake manifold temperature starts nearing
200F on a cool evening.  It gets easily above 300F by the time the
wastegate opens.  This is where intercoolers come in.  Technically they
are an aftercooler since they come AFTER the turbo, but that's just
for information. :)  Cooling the intake air down increases the O2 density
in the cylinder even more.  :)
  EGT, Exhaust Gas Temperature.
The hotter it is the faster your turbo will spin.  It's measured with a
Pyrometer.
They cost about $125 and are well worth it on a TD.  Hotter EGT comes from
more fuel being burned under load conditions.  Without load the engine isn't
working hard enough for the pump to inject enough fuel to make high EGTs.
Maximum EGT is considered to be 1350 PRE turbo.  That makes for about
1200 to 1250 POST turbo.  Hotter and you run a good risk of blowing aluminum
off of the pistons!  Generally you get black smoke when you're running
at or above these temps.  Not only does hotter EGT make for a faster
turbo spin speed but engine rpm does as well as load.  They all work
together to increase the volume of exhaust leaving the engine.  Volume
is made from the heat expansion as well as the direct pumping of air.
  Fuel:
  First you have a pump that draws fuel into the injector pump.  It's right
in the front and that's why the front seal failure will cause the engine to
not run.  The pump sucks air instead of fuel.  Then the fuel is metered
and timed with the injector pump.  It is atomized into the prechamber
by the injectors.  Some excess fuel goes back to the tank from the
injectors and a fair amount of excess fuel returns from the pump.
  As the engine runs faster, timing must advance in order to keep the
peak pressure at optimum.  Fuel volume increases per stroke, in order
to have more speed or power than at present.  This happens by pulling the
"throttle" lever thus stepping on the pedal.  The injector has a high
pressure
spring in it that requires around 2400 psi to overcome.  When the line
pressure exceeds the spring pressure, the injector's pintle lifts enough to
allow the fuel to spray into the prechamber as a very fine mist.  Bad
injectors will put out larger droplets in a good pattern at best.  They can
spray to one side instead of a full cone or down to just a stream.  Pressures
can be too high or low or the pintle can leak causing dripping.  These all
waste fuel and cause a loss in power and economy as well as possible
engine damage.
  On a TD pulling the throttle increases the fuel in a fairly linear fashion.
 When
you have turbo boost, then you have the potential for more fuel to be added
and efficiently burned.  The aneroid in the pump has a diaphragm that the
boost pressure pushes down against a spring.  As the diaphragm goes
down, an attached rod, with an eccentric cone at the end, also goes down.
There's a pin that rides on the cone.  As the cone goes down, allowing the
pin to protrude further, the fuel increases even more.  The further down it
goes, the more fuel that is "automatically" added regardless of the
throttle position, so long as it's still sufficient to maintain boost or an
increasing boost condition.
  Adjustments:
These should really only be done with a pyrometer installed.  You want to
maintain a safe EGT at all times.  It's too easy to exceed that with a turbo
and lots of fuel.
  First is the main, maximum fuel volume screw.  This is an external
adjustment with a lock collar welded to it, to prevent increasing the fuel
beyond a safe limit.  There's usually enough slack to get you as far as
you need to go.  In is more, out is less fuel.  TD or NA, this should be
set for a light waft of smoke when at full throttle but before the boost
kicks in on a TD.
  The adjustment on the top of the aneroid sets the starting point of the
cone.  I don't know what the recommended setting is and unless it's been
dinked with, it's probably fine. General consensus would be to set it for
maximum travel potential for the cone.  Therefore it would be set so the
pin would be at the edge of the large end of the cone at rest, with the lid
on.
  Spring perch.
  This is under the spring, beneath the diaphragm.  Lowering it will decrease
spring tension, allowing fueling increase at a faster rate, with less boost.
Raising it requires more boost to achieve full enrichment.  This would be
for adjusting too much/no smoke during full/near full throttle acceleration,
while under boost condition.
  Cone rotation.
  Be sure to note where the diaphragm is "clocked" before any adjusting.
There is a dot stamped into the top of the large washer holding the shaft
to the diaphragm.  Pull the diaphragm and note where the closest and
farthest points are for the relationship of the cone to the OD of the shaft.
These are your leanest and richest settings respectively.  It's usually set
somewhere between midpoint and leanest.  Too much fuel would be smoking
at full throttle and after achieving or nearing full boost.
  Smoke is defined basically as black smoke visible through the rear view
mirror in daylight.  If it looks brown or gray, due to density, then you're
close to maximum.  If it's black back it off.  You just waste fuel, increase
wear, buildup and contamination of the engine and irritate other drivers.
Not that a nice smoke screen isn't nice once in a while, but it adds to
the misconception about our diesels being dirty, stinky and so forth.
  Hope this answers a few questions.  :)
     Loren