Barely-running '89 90q

Huw Powell audi at
Mon Apr 5 15:15:55 EDT 2004

> Thanks for the guidance Huw.  Unfortunately nothing seems to be
> malfunctioning- I must be still missing the gremlin, or he is quick and
> invisible.  Temp sender good according to Bentley specs, fuel dist. pot good
> (I knew that 3 wire harness connector from the junkyard would come in handy
> someday!), both WOT and idle switches work as expected, dpr current measures
> good (100 mA w/o engine running, down to 10 mA for the 'functionality' test
> when the WOT switch is closed and the engine is stationary, varying current
> with engine running, tracks with O2 sensor installed, steady with it
> unplugged and grounded)

the dpr current is supposed to oscillate around 0 mA, up and down a few 
mA, with the engine warm and running, at idle.

If you unplug the OXS there is no need to ground it.  If you ground the 
signal wire to the ECU, teh ECU will overreact and try to compensate.

> O2 is all over the place, but unplugging does not
> remedy the situation.  CSV ok, unplugged it with no change, grounds good and
> air filter clean.  WTF?  
> Is it possible to send a steady 0.7v to the computer in place of the O2
> sensor voltage (fake it out)? 

If you simply unplug the OXS, the computer has a 0.5 volt reference of 
its own that will allow the engine to run at the static mixture setting.

A working OXS should oscillate up and down between about .2 and .8 volts 
while the dpr is doing its thing (in reaction to the OXS cycling).

Huw Powell

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