89 Audi 90 stumbling

[Mark Rutherford]

I have a 1989 Audi 90 that has developed a hesitation.  I own several Audi's
and have done all of my own repairs for over a decade.  However on this one
I am stumped.  I hope the group can give me some ideas about where to turn
next.  

 

History:

About 5 years ago I install a manual transmission to replace a failed
Automatic.   Drove the car for about a year no problems.  The car sat for
about 4 years after that.  This spring I decided to sell the car.  To get
the car started I installed a old fuel pump I had, and fixed a vacuum lead
in the intake boot.  Car ran fine for about a month.   

 

Symptoms:

Car will be running fine and then loose power and shake under acceleration
then recover and run fine.  The problem has become more frequent with time.
It will not do it when it is cold but will start to before it reaches full
temperature.  It will happen repeatedly when making a right turn.  Will
sometimes do it when driving straight.  Rarely does it turning left.  

 

Repairs done so far:

When investigating the problem found that there was no bulb in the check
engine light.  Installed one and tried to pull codes.  Check engine light
will turn on when jumping diagnostic  connector, but will not flash codes.
Placed LED in diagnostic connector with appropriate resistor, no codes.  Put
a volt meter across the connector and found the ECU was producing codes but
at a voltage of 1.5 volts, I do not know if this is normal for this car but
I do not believe it is.  Also noticed small unchanging voltage from o2
sensor ( .2 volts ).  Adjusting the mixture produced no change in o2
reading.  Replaced o2 sensor.  No change in problem or o2 readings.

 

1.       From the pulses on the volt meter found a code for the knock
sensor.  The insulation on the cable was rotted away and in general bad
condition.  Replaced with new sensor torqued to 22 Nm.  No change in
problem, ECU produces 4444

2.       The used fuel pump was making noise, replaced with new one, no
change.  Also replaced fuel filter.  Read an article in the archive about a
strainer on the fuel head that can become plugged.  Removed it per archive
suggestion.  Still no change in problem, ECU 4444.  The car will run fine
under full load in high gear up hill for several minutes.  This leads me to
believe the fuel system is capable of delivering the amount of fuel needed.

3.       Since I have a parts car I changed. 

a.        The coil, No change

b.      Installed additional ground wires from the battery to the intake
manifold, engine, body and bell housing.

c.       Coolant Temp sensor - No change

d.      Fuel distributor including - No change

                                                               i.      Fuel
head

                                                             ii.
Potentiometer

                                                            iii.
Differential pressure regulator

                                                           iv.      Fuel
pressure regulator

e.      All of the o2 sensors I have seen produce a voltage that changes
from about .4  to .6 volts.  This one produces a steady voltage between 0
and .5 volts depending on the mixture.  Adjusting the mixture full rich
until the motor dies still produces a reading of .5 volts.  Install a new O2
sensor same results as above.   The above happens plugged in on not.  This
part still makes no sense to me.

f.        Changed ignition computer - No change

g.       Changed fuel computer - no change in problem , but the check engine
light works as it should.

h.      Checked wiring from All data CD and diagnostic procedures.  No
problems found.  

i.         The car had a exhaust leak, thought that it could be pulling in
air and effecting the o2 reading.   Repaired the leaks - problem still
there.  O2 still behaving strangely.

 

I really do not know where to go next.  Only things out of the ordinary are
O2 sensor reading, and check engine light with original computer.  I have
not check fuel pressure, due to lack of tools.

 

 

Thanks for any help

Mark Rutherford