Fuel Injection Questions- MB engine

[scottmo <scottmo@prodigy.net>]

Phil,

>From your description it sounds like your MB engine
CIS system might be the same as what was used on 
the mid 89-90 200TQ US model cars, with the 
higher compression dual knock sensor MC engine,
which is in my 89 200TQ....I will describe
how my system works and you can then see if the
system used on your MB engine is the same or similar.

NOTE:  The 86-88 5000TQ and early 89 200TQ (single knock sensor
MC engine) did have a system pressure regulator inside the fuel
distributor metering head but in mid 89 when they went to the
higher compression dual knock sensor MC engine and at
the same time they changed the fuel distributor metering head
with different fuel injector lines and higher operating 
pressure Viton Tipped fine thread injectors ( 035 133 551F) 
They removed that internal system pressure regulator inside the fuel
distributor and used a remote mounted  system pressure regulator
like the one you described. The system pressure listed for 
MC engines from the Bentley is suppposed to be between  
5.8-6.6 bar but I don't know if the Bentley info was
updated to correctly reflect this change to the 
remote mounted pressure regulator. 

The part number for the system pressure regulator 
that is used on my 89 200TQ car is
a 034-133-534L. My fuel pressure regulator
has a hose conected to it but I believe the hose just goes
down into the air filter housing, and is open to the atmosphere.

This remote mounted system pressure regulator looks similar
to the one used on the NA CIS-E-III systems but on these
systems they did not use a warm up regulator or
the frequency valve. They had a differential pressure
actuator that is mounted on the side of the fuel 
distributor and used an electronically  controlled 
 current to tweak the mixture for cold running
mixture enrichment and for O2 sensor mixture tweaking.
The CIS-E-III system pressure is spec'd to be
between 6.1-6.5 bar. 

The Bentley manual for my 89 200TQ dual knock sensor
MC engine does not document this change to
the different fuel pressure regulator very well at all.
This system seems to be a bit of a bastardization of the 
newer CIS-E-III system parts and the older MC single
knock sensor CIS system.

The fuel distributor used on my car has a part number of
034-133-481C and the warm up regulator used is a 
034-133-403A (this warm up regulator was used on the earlier
86-88 5000TQ MC engines as well) The Control pressure 
with the engine oil temp between 50-70 degrees C is 
supposed to be 3.4-3.8 bar.The cold 25 C control
pressure is spec'd to be 1.6 bar.

These warm up regulators have a vacuum port
that is capped off with a little black plastic cap 
that has a slot in it which keeps out water etc
but still allows atmospheric pressure in 
to the regulator chamber. The lower atmospheric pressure
acting on the internal diaphram effectively increases the
control pressure on top of the fuel metering plunger at 
higher altitudes and provides some altitude compensation
to help lean out the mixture.

My understanding is that the metering valve control pressure
is regulated for the most part by the warm up regulator but
I imagine the system pressure regulator does do
some tweaking to the system pressure at different
altitudes and this could affect the control pressure slightly.

These systems use the frequency valve
to tweak the overall mixture at mid-full throttle,(low to
high boost levels). In the US the frequency valve is also
used to tweak the mixture slightly from the O2 sensor
feedback signal.

Does any of this match up with what you have on your
car and does it make some sense as far as the operation of
your system?
let me know...
Scott M.
 

>Brief recap - the MB engine's "warm-up regulator" is exactly that.  >There is no  vacuum connection for fuel enrichment.  
>Question one - is this device (a warm- up regulator with no provision >for vacuum control) unique to the MB?
>The MB also doesn't have a system pressure regulator inside the >metering head. Instead, it has a "pressure regulator" valve 
>mounted on a bracket behind the fuel metering head.
>MUCH TEXT DELETED
>Phil Payne
>phil@sievers.com
>Committee Member, UK Audi [ur-]quattro Owners Club