Fuel Injection Questions repeat

[Phil Payne <Phil@sievers.com>]

In message <335AFE10.931@prodigy.net> scottmo writes:

> Phil, here is a copy of the original message.

Thank you.  I grovel.

> >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.

Despite the microfiche refering to "the first knock sensor" and
perceived ur-quattro history stating that the MB has two - I can only
find one.

> 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.

Check on the injectors - the parts fiche says 035 133 551F, and so does
a recent invoice.  Knowing the abilities of some of the garages - how do
I tell the difference between these and the earlier 049 133 551A fitted
to WR engines?

My microfiche says 5.6 to 6.3 bar.

> 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.

Part number checks again.  I wonder if this is meant to be the altitude
compensation on this engine?  If so, plumbing it to the intake plenum
would cause my symptoms ...

But what is the vacuum tap-off on the intake plenum for, otherwise?

> 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.

No - nothing on the side of the metering head.

> 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.

Amen to that.  If it's a copy of the 200TQ German fiche, and the
200TQ fiche are as thin as the ur-quattro fiche ...

> 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.

Yup.  That's how it seems.

> 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.

My metering head is 034 133 481J, and the warm-up valve is
034 133-403K.  Control pressure (warm) is 3.4 to 3.8, and 1.8 to 2.3
at 25c.

> 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.

Older (WR) warm-up regulators have a vacuum port on the _side_.
Mine doesn't - just a dust cap on a port on the top.

> 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.

I wonder.  I would _love_ to know that device's nominal specifications.

> 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.

Seems logical.

--
 Phil Payne

 Phone: +44 385302803  Fax: +44 1536723021  CIS: 100012,1660