[Vwdiesel] Need help getting parts from Germany

[Charlie Smith]

Earlier, LBaird119 at aol.com wrote:
>
> charlie at elektro.cmhnet.org writes:
> > The solution to this, is to advance the pump timing.  Advancing the pump
> >  timing lets you get more fuel in (with the longer duration) and still
> >  lets the burning get finished before the exhaust valve opens.
>
>   I've seen info to the contrary.  There's a web site out there about really
> cranking the power out of semi tractor's engines.  Their whole idea is
> high performance, along with good economy and equal or better longevity.
> Once they really start pouring the fuel to them, they RETARD the timing
> to keep temps down.  Most combustion related issues in a diesel, do
> about the opposite of a gas engine.

There's other things involved there.  Ignoring the difference in engine
sizes, most of their injection pumps are have very much more fuel capacity
per injection than the Bosch pump used on VWs.  This means their time
(in degrees of engine rotation) to inject the required fuel is much
shorter.  So even if they are turned up to put more fuel in, the total
time to get it injected is still short.

The VW injection pump doesn't have the "capacity per injection" to do this
in just a few degrees of rotation.  I've personally observed the problem
I talked about.  On a VW the solution would be to install a larger
capacity injection pump, if such an otherwise compatible pump were
available.  I'm sure it would be expensive.  Injection pumps for the
Cummins engine as used in my Dodge truck are well over $2000.  Lacking
a larger capacity pump on a VW, if you are going to put a lot more fuel
in per injection then you need to watch the exhaust temperature.
Using higher capacity injectors isn't really an option, since it's
the injection pump that governs how much fuel gets put in per degree
of crank rotation.  Common rail systems that use electric injectors
can have fueling increased by either longer injection duration or
by using larger capacity injectors, or both.


>   You can also claim you're changing the timing every time you step
> on the throttle.

Not true.  Stepping on the throttle only changes the max amount of
fuel injected per injection - which means the "time to inject" gets
longer, it takes more degrees of pump (or engine) rotation to get all
the fuel put in.  The point of BEGINNING injection stays the same.
(Understanding that moving the throttle is done with the engine
at the same speed).


> The timing advances with relation to speed and pump pressure.  I think
> it's mostly dependent on internal pump pressure.

True.  The advance (of the point where injection begins) is a factor
of internal pump pressure pushing against a spring loaded piston that
adjusts start of injection time when it moves.  This advance is adjustable
by changing shims on the spring, which you generally don't want to do.

Internal pump pressure is created by the sliding vane pump next to the
pulley.  This pump brings fuel from the tank and circulates it through
the pump and back to the tank.  There is a restriction in the pump
return line banjo bolt that causes pressure to build in the pump as
rpms increase.


> TD pumps don't alter the timing as they move into the boost enrichment,
> which greatly (relatively anyway) increases fueling.

Right.  The increased fuel is a result of fuel being injected for a
longer duration.

    - Charlie


  Charlie Smith   charlie at elektro.cmhnet.org  614-471-1418
  http://www.elektro.com/~charlie      Columbus Ohio   USA
  http://www.elektro.com/~audi     photos & technical info

  95 S6 Quattro  -  24 PSI, RS2 6 speed, and other features
  97 Dodge Ram   -  35 PSI, 4x4 w/Cummins turbo diesel