Fuel Injectors, poor starting, rich running

["Scott M." <scottmo@teleport.com>]

Mark,

Regarding your rich running condition, you can remove the
cold start valve and see if it is leaking when the fuel
system is pressurized. (reconnect the CS valve fuel line!) 
The ECU normally only operates the cold start valve during
cranking for a few seconds and briefly during initial
acceleration with a really cold engine <32 degrees F. If
the engine overheats from hard running/high boost operation
the multifunction sender will direct the ECU to use the
cold start valve to briefly richen up the mixture and cool
things down. 

Leaky injectors will cause the hard start condition as you
mentioned, one person from this list found his leaky
injectors by removing them after shut down and then placed
them inside plastic bags and then checked them for seepage
the next morning. The injector inserts, air shroud
cones/o-rings and injector o-ring (use green Viton type)
should be replaced while you are in there.

Here are a couple of other items you may want to check
regarding the rich running/black soot etc.

Fuel System pressure, normally ~5.8 - 6.6 bar (pressure
regulator may have gone haywire)

Warm up regulator control pressure after warm up. 3.4 - 3.8
bar. If the control pressure is too low you will get a 
richer mixture. (also verify the electrical heating element
connection and voltage supply are ok as well as the
internal heating element in the warm up regulator )

Basic Idle mixture adjustment (frequency valve duty cycle)
35-50% assuming no vacuum leaks.
You can also use emissions tester and adjust for 0.6-1.2%
CO upstream of the cat with O2 sensor disconnected,
breather hoses removed/plugged. Blue orifice cap removed
from fuel dist boot. also remove the two connectors from
the evap canister vent solenoids.

Engine oil severely diluted with fuel

Plugged up air filter

Fuel distributor plunger could be sticking

Check the ECU Coolant temp sensor which is located at the
front area on the cylinder head just below the power
steering pump mounting bracket (resistance  aprox 1000 ohms
at engine coolant temp near 68 degrees F) The resistance
gets lower as the temp goes up. Check sensor wiring to the
ECU.

O2 sensor wire could be grounded. Low O2 voltage tells the
ECU to richen up the mixture via the frequency valve.
Disconnect the O2 sensor, basic mixture adjustment will
determine idle mixture.

HTH
Scott M.
Vorsprung Durch Technik

>My symptoms are;
>
>1. Hesitating startup.
>2. Carbon fouled plugs
>3. Heavy black soot build-up on exhaust
>If anyone can steer me in the right direction please do,
before I begin to
>dump a lot of cash on parts that I don't need. Thanks
>Mark 90 200T