Re:Bosch L-Jet

[James Montebello <jamesm@domain.elided>]

On Sat, 12 Oct 2002 GLewis4457@domain.elided wrote:
> In a message dated 10/12/2002 1:09:03 PM Central Daylight Time,
> owner-alfa-digest@domain.elided writes:
> > >   The Bosch L-Jet has two identical inductive pickup sensors on the
> > >bellhousing.  One reads a trigger pin for TDC.  The other reads the teeth
> > >off the flywheel for engine rpm.
>
> Maybe it changed later, and maybe was unique to the L-Jet Spider, but my
> L-Jet equipped '83 GTV6 has no inductive pickups, period.  Also, it is NOT
> shown in the L-Jet schematics.  These were present on my previously owned '93
> 164L with Motronic.

Quite correct.  No L-Jet setup used the flywheel sensors.  L-Jet is
fuel only, and you don't need the position of the crankshaft for fuel.
All L-Jet systems used the tach signal as the engine speed signal.
Some Alfas (later GTV6 and Milano, maybe some Spiders) had a completely
separate electronic ignition setup, but this isn't part of L-Jet per se,
and they certainly the GTV6 system used a distributor for timing and
distribution of spark.

Motronic systems combine fuel and ignition in one unit, and ignition
needs a crank position to work.  Early systems used the flywheel
sensors.  One sensor to read engine speed off the flywheel ring gear,
or a separate set of teeth on a few cars, and a second sensor to read a
pin for crank position.  Later Motronic systems used a dedicated wheel
attached to the nose of the crank, with missing teeth to determine
crank position.  Later ignitions (as on some 164s) used coil-on-plug,
and had no distributor.  Some Motronic cars have a simple distributor
that only distributes spark and have no advance mechanism.

Bosch is Bosch, and there's little variance between cars from BMW,
Porsche, Mercedes, Volvo, and Alfa, all of whom (among others) used
off the shelf Bosch systems.  A copy of Charles Probst's book on Bosch
systems will tell you just about everything you need to know about how
to identify, diagnose, and fix these things.

james montebello
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