1989 A90Q gas mileage

[Huw Powell]

> I had some work done on the engine and the car ran really well.  The
> mechanic asked me to bring it back in to have the oil changed and "set" the
> engine.  Ever since this was done. my gas mileage is awful.  I'm lucky if I
> can get 425 Kilometers from 50 liters of highest premium gas.

I assume you were measuring fuel economy when it was "running great" 
before the "adjustment"?  Does it still "run great"?

Excuse me while I translate for myself...

425 * 0.621 = 264 miles

50 * 0.264 = 13.2 gallons

so, 20 mpg in medieval units.

> Any suggestions on what might cause such poor gas mileage suddenly?  I can
> smell the exhaust when I start the car and stand about 8 feet away from the
> car.

Well, 20 mpg isn't *awful*, but the car should do better.  Something is 
wrong... as long as the "adjustments" were within "ECU correctable" 
range, the engine should be running fairly efficiently whenever it's 
warm, if all the devices are working correctly.

If all is working and the adjustments were done properly, I'd expect 
23-26 mpg (based on experience with my US model), or about 20-25% better 
than you report.

So... you might have vacuum leaks, malfunctioning sensors or senders, or 
gross misadjustment.  I'd suspect the former two being causes and the 
latter being a result.

The exhaust smell (do you mean unburnt fuel?) when cold might mean 
things are set way too rich, perhaps even too rich for the ECU to 
compensate when in closed loop (warmed up engine).

If you can, it's time to measure things like OXS output voltage when 
warm, ECU NTC sender resistance cold and warm, CPA current, etc.

Also check over typical "tune up" parts for age, etc. - air filter, 
plugs, wires, cap and rotor, etc.

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/