lack of power issue

[michael]

Car: 1990 200 Quattro 10v turbo.  TAP chip and wastegate spring, K&N filter,
both installed by previous owner.

Symptoms: In gear, RPM won't reach 4000, severe loss of power, feels like
there's no difference between 10% and 100% throttle, boost never above 0.9 bar
as indicated by stock digital gauge.  Car struggles to accelerate, to get up
hills, etc.  This started suddenly, no indication, no noises, nothing.


Replaced: thermostat, multi-function temp sensor, throttle position switch,
plugs, wires, distributor cap & rotor, coolant, fuel filter.


Tested: compression looks good
intake path from airflow sensor pressure tested, no leaks whatsoever
ECU reports 4-4-4-4, no check engine light
all fuses intact, all necessary relays present but untested
audible whine from fuel pump
turbo spins freely, no shaft play
throttle opens and closes properly, and fully
spark plugs a medium-light tan color
temperature as indicated by dashboard gauge appears within range
idle stabilization valve seems to buzz happily
idles fine (other than minor warm start issue)


At this point, I think the next things to try replacing are going to be
expensive.  I'm guessing it's a fuel delivery issue, the fuel pump sounds a
little sick.  Though I'm comparing that to the Walbro pumps in my other two
cars, I don't know if they're supposed to sound the same.  I also thought
possibly it'd be injectors, or some part of the fuel distributor setup.
Really, I don't know these cars well enough yet.  Also, I plan to change the
oil... not that it will make any real difference.

I read that there's a screen somewhere in the fuel distributor that sometimes
gets clogged, have not yet taken it all apart to test this, it was to be my
next step.

I do not have volume 1 of the Bentley manual (though I have the other two,
previous owner must have misplaced that one).


Anyone have any ideas?  

-- 
Michael Stella - http://www.thismetalsky.org 
'97 AWD Eagle Talon & '92 Galant VR4 #1000/1000 & '90 Audi 200 Quattro