Sudden Drop in Gas Mileage

Since I purchase my '96 SL2 used with 29K miles, I've gotten a consistant 26
MPG in town (auto). It has suddenly dropped to 21 MPG. As far as I can tell,
the performance is the same.

Any ideas?

Doug in Fremont CA

 

How many miles does it have now? If over 50K you should check your 02
sensors. If they are sluggish but not quite failing enough to set a code
you will lose efficiency.

 

How do you check O2 Sensors? I have a 98, 94000 mi, and have recently
experienced a similar drop.

 

I've got 40K miles on the car.

 

Check the coolant temperature sensor.

They fail often on Saturns.

One mode of failure is they think the engine is cold and they run it rich.

 

Check the coolant temperature sensor.

You would also notice a high idle if this is the case. Also, the fan would
never come on unless you put the A/C on.

 

You need an o-scope to properly check 02 sensors. Best bet is to take the
car to a mechanic/dealer and have them hook up their scantool and perform
the diagnosis for you, one or both of them may be sluggish.

Alternatively, 02 sensors are relatively cheap, buy them at your favorite
parts store and replace them one at a time or all at once. The upstream
(first in line) sensor is the one that tells your computer to lean or richen
the air fuel mixture, the downstream one monitors catalytic converter
operation.

All this is of course assuming that your SES lite is not on and no DTCs are
set.

Ed

 

How does one test this little monster, as I have all the symptoms listed above
(or, rather, my '95 SW does).

 

You can test its resistance. I BELIEVE there is a table of accepted values for
each temp range in the Haynes manual. But its probably easier to just change it
if you exhibit the symptoms - it was only about $11 at NAPA to replace mine.
Regardless, its cheap insurance since it is a very common failure on Saturns.

 

Thanks. If anybody wants me on Sunday, I'll be out in the garage.

 

You can test its resistance. I BELIEVE there is a table of accepted values

If you're looking to get away, you may want to find more stuff to do, since
replacing the CTS shouldn't take you very long

 

Bah. Had a list of things to do - all those little five and ten-minute jobs that
pile up; was going to get 'em all done. Unfortunately, something's come up and
I'm going to be busy tomorrow. Guess I'll do it next week.

 

I had the same problem on a 94 SL2.

After many times to the dealer I found out my oil level was not high
enough. Topped it off and that was that. Could not believe it was
that simple.

Since then I always check the level. Check the obvious.

I did have that sensor replaced as well as it was failing but did not
fix my mileage.

 

same problem on a 93 SL1, it was MAP sensor