4kq bad mileage (still!) (longish)
audi at mediaone.net
Mon Feb 4 18:18:46 EST 2002
> Checked the injectors. They flow fine. Recent plugs, wires, cap, rotor, 02
> sensor. CO within spec. Cars runs well.
> I have a new thermostat (87-92C).
> BUT, my mileage still sucks (17mpg).
> Huw, I saw something on your site where you cleaned up the ground contact
> (bolt) at the upper rad hose flange. You mentioned that a bad ground could
> mess up temp signals (voltage) to the ECU (and the gauge I guess). After you
> did that, did your mileage improve a lot? Or was your only problem the
Don't think I had a problem, just had to make sure the circuit
functioned when assembling.
> Now, on the flange, there are 2 sensors. Top one is the gauge sender, and
> the bottom one is the thermo-time switch, right? According to Bentley, it
> and the temp gauge sender don't have separate ground wires, so they go to
> ground through the housing, right?I guess cleaning up the flange bolts and
> the threads on the sensors might fix my gauge, but that's it.
the thermo time switch is something different. The one you are looking
at is a negative temperature coefficient (NTC) switch, in that its
resistance varies with temerature. This tells the ECU whether to run
rich on the cold start "map," in open loop, or to go into closed loop
and let the OXS signal determine mixture.
The device should be removed and tested, your Bentley has specs for cold
and warm resistances - ice water and boiling water make great
"standards" for immersing it (carefully, boiling water hurts!), although
they are more extreme than the spec temps.
> So, where's the "temp sensor (NTC)" that the Bentley shows on 97.270 track
> 27? It grounds by wire to the intake manifold? It goes to the ECU. My guess
> is that's what I'm looking for for my mileage woes.
yup. that's the one in the coolant flange. there are ground wires at
the intake manifold, two of them I believe, what kind of shape are they
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