[Vwdiesel] Jetta 1.6L TD tests/fuel economy

[Mike & Coreen Smith]

Loren & Group,
RE: My new-to-me, 1988 Jetta GL, Turbo diesel "turbo testing" and achieving
fuel economy. (first tank was 45mpg Imperial)
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After pumping up the tires today to 35psi,(some were down quite a bit)  I
decided tonight to take everyones suggestion and turn in the max fuel screw
1/8th turn.  My locknut was a 13mm (not a 10mm as some had mentioned)
I did that, and took it for a spin up the road and could just see a hint of
medium blackish smoke. I don't think much of a change from before, but think
I'll leave it at that for this tank of fuel and see.  I also took the
stock-ish, Canadian-Tire air filter out and blew it out as best as I could
with my air compressor.  It wasn't that dirty at all, slightly brown, with
only one end with anything resembling black on it, but I did get some fine
particles out of it just the same.
I topped up the oil (which was probably down almost a liter ) and will see
what all these changes bring.

I know for a truly scientific experiment you should only change one variable
at a time, but I couldn't resist, ha ha.
I'd already burned 1/4 tank of fuel (& ~230kms) before making these changes,
so this test won't be a true test over a full tank of diesel anyway. Oh
yeah, the back tires are brand new as of Friday too. Surely couldn't hurt.
The old ones were balding.

I'd sure like to get the 92mpg the rabbit got. (was it Hagars??)
Mike
P.S.- I am still doubting the aneroid/cone/whatever setup is *really*
working..........LOL

----- Original Message -----
From: <LBaird119 at aol.com>
To: <ve9aa at nbnet.nb.ca>; <vwdiesel at vwfans.com>
Sent: Sunday, April 13, 2003 3:48 AM
Subject: Re: [Vwdiesel] Solenoid valve on turbo-line test *RESULTS*


> > 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
>