I just had a similar problem on a 85 van I was working on.  I changed the
injectors over from a good running motor, and also the fuel pressure
regulator with no results.  I then hooked up my digitool (thanks Darrell) and
immediately I saw that the readings for the temp II sender (in the thermostat
housing) were way wrong.  They were telling the computer that the motor was
super cold and it was flooding the engine at any time except stone cold.
I changed the temp sender and the problem was magically gone.  You can test
this sender with a multimeter and the Bentley Manual (Digitool is cooler
though).
I have these temp senders new for $30 each, if you find you need one.

Hope this helps.

Ken Wilford
http://www.vanagain.com
John 3:16
Phone: (856)-765-1583
Shop:   (856)-327-0027
Fax:     (856)-327-2242