[s-cars] UrS4 injector-electrics mystery - mechanics stumped - ideas please!?

[leigha]

Hi,

I’ve got a ’92 UrS4 with a strange injector (and ECU read-code-comms)
problem.  Several very-audi-experienced mechanics from 2 excellent shops are
currently stumped and my car has been in the shop for over week.  Diagnosis
theories have about run dry.  Getting desperate for ideas to try.

Any ideas for root causes or new diagnosis tactics?

1.	Injectors (mostly) fails to get any electricity to them. Don’t fire.
	a.	About 2-3 times out of 10, when try to start motor, it runs for 25s-30s
then motor quits. Other 7-10 times won’t fire at all.
                                                               i.      Put
LED test-light in the circuit with injectors to detect electric supply.
Light correlates perfectly with symptoms in (1.a.)
                                                             ii.      Tried
circuit breaker located near ECU in footwell. Fine.
                                                            iii.      To
diagnose if any motor/cam/rpm speed sensors (there are 5 I think) try to
read codes.  Get msg “No communication” or something similar
1.       Tried ECU out of a live donor car. No change


2.	Attempt to read codes from ECU.  ‘can’t communicate’ with anything but
the climate control.  ABS and motor codes – no commo.
1.       Tried ECU out of a live donor car. No change in communication.


Might be unrelated, but this injector-electrics problem happened either
coincident with an on-road fuel-pump complete failure (after about 20-30
min. of stumbling). This injector problem surfaced for the first time
(apparently) in the shop right after replacing the fuel pump.

Leigh Anderson,
’92 UrS4, Audi Club PNW instructor
Portland, OR