[s-cars] Cold weather and lousy fuel mileage

[Peter Schulz]

Stott:

Do you have a Vag Com?
A potential cause is that the ECU is overly compensating for the cold 
weather for start up and then continually running super rich.
Have you checked the temp sender in the back of the head on the passenger side?

I would also check the O2 sensor to make sure that its still working to spec.

-Peter



At 01:12 PM 3/9/2007 -0500, you wrote:
>Weather here in the Northeast has had the temps hovering around 0*F, and my
>fuel mileage has gone straight to the toilet.
>
>Nice weather (40*F>) and 95% highway I can pull 21mpg and around 400 per
>tank.  Cold weather and 85% highway and I watch my mileage plummet to 16mpg
>and maybe 250-300 miles a tank.  Watching the TDS1 when the outside air temp
>is an indicated 0 - 15*F  shows an intake air temp ~20-25* warmer.
>
>Patient is a 95 S6A with 252k on the clock.  Still stock.  Receives routine
>maintenance.  She plugs, oxy sensor and fuel filter were done around 204k so
>they could be considered due, but I would expect that to cause decreases
>across the board, not temp specific.  Coolant temp is rock solid at the
>first fat bar (~10 o'clock).  Multi-function temp sender was done at 204k.
>The HVAC temp sensor in the coolant line between block and heater core
>replaced about 230k.  No CEL or codes.
>
>My prior experience with the CIS cars didn't yield such temp sensitive
>performance, if you had the car tuned right and all sensors working.  Is
>this something particular to the Motronic / hot-wire MAF systems?  Is the
>incoming air so cold that the hot wire isn't?  I don't have my mixture gauge
>in at the moment, but I suppose I will hook it up this weekend and watch
>mixture over the next week.  When I had it hooked up in normal temps
>previously (within 5k), mixture behaved as expected at idle and cruise, on
>throttle and off.
>
>This just the way things are? or is this an indication of a (temp) sender or
>something that is begging for replacement.
>
>Thanks!
>  -Stott
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-Peter Schulz
Chelmsford Ma, USA
http://www.naaclub.org/

1995.5 S6 Avant Emerald/Ecru
1995.5 S6 Avant Silver/Platinum

1991 200 20v Q Avant Titan Grey
1991 200 20v Q Avant Indigo Mica (for Sale)
1991 90 20v Q Red

1990 CQ silver  (sold)
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