Date:         Fri, 19 Sep 1997 16:17:50 -0400
Reply-To:     CarlMarin@AOL.COM
Sender:       Vanagon mailing list <Vanagon@Gerry.SDSC.EDU>
From:         Carl Turner <CarlMarin@AOL.COM>
Subject:      Re: VW Fuel Injection Information (was SS header)

In a message dated 97-09-19 08:12:18 EDT, you write:

<<
 Now these operations have legal questionability, beware there is an
 oxygen sensor attached to the cat, and performing one of the operations
 will change the reading.  I have no idea of that impact on the FI
 system.
  >>

On my 84 at least, the O2 sensor is upstream of the cat and as such cannot
have any impact on the way the FI works.  I replaces my cat with an
aftermarket cat that fits very nicely, was slightly smaller overall, and has
a port which I left plugged at the "plenum" at the input side of the cat for
installation of an O2 sensor.   This is also on the upstream side.  In rough
terms if memory serves me, one adjusts the Vanagon to around 1/2 a percent CO
at the upstream sniffer port and this will result in about zero CO at the
tailpipe if the Cat is warmed up and everythng is working right.  It is
possible to get the mixture so far out of whack that the O2 sensor cannot
compensate.

Also a point to remember is that the O2 sensor needs to be hot to work.
 Mounting out by the tailpipe would be mostly useless I would think.  The
three wire type O2 sensors that many cars have encorporate a heating element
to get the sensor up to operating temperature faster.  Otherwise these behave
towards the FI system exactly the same as the one wire.  The O2 sensor is
after all simply a variable resistor.  (for diagnostic work only ;^) you
could of course just install a variable resistor to tailor the FI
caracteristic if you were the experimenting type.

Excellent reference on how these Bosch Fuel injections actually work, not
just the Bentley's service manual cookbook, is "Bosch Fuel Injection & Engine
Management" by Charles O. Probst, SAE, published by Robert Bentley.

Digijet is a VW name for the Bosch L-Jetronic with Lambda (Lambda is Bosch
speak for an Oxygen sensor feedback loop)

The book covers the operation of the L-Jetronic in gory detail (I have the
'84 Digijet).  The Digifant I on the later Vanagons is apparently a partly VW
designed system, pulsed injection like the Digijet, similar in operation to a
Bosch Motronic with a less complicated timing map than has the Motronic, and
also lacking the Motronic Knock sensor.  (So the book tells me)

If you work on the rear end of your Vanagon, get this book!

Probst mentions some interesting things about Jump Starting and battery
charging a car with Bosch FI in chapter 4.1.3.  Concerns excessive voltage
spikes effects on the control unit.  Worth pondering.  When I get my recently
ordered Owners manual I will have to see if they say anything similar.

Carl Turner
84 Worstfalia project