I have a 92 fwd AT, I have done the plugs , filter cleaned, checked vac hoses pcv and the mpg is still horrible. Have had this car since new and never got such poor mileage. CEL not on . any ideas? Should I sent to a mechanic to check out?

How many miles?

 

The O2 sensor could be getting tired.

If you detect an engine "miss," or know that the plug wires are old, a new set of wires would certainly help.

 

Yes, I read that you checked the pcv valve, but if old, I would replace it. It doesn't cost much.

Car has 127k. The wires are relatively new and I did put in a new PCV. The car runs fine.

 

Is the o2 sensor in the engine or just above the converter? If I can replace it myself, will try. Where is the best place to buy a replacement? online or pep boys type store?

Also consider the possibility of a bad coolant temp sensor (the one for the engine control computer.) I am assuming that the car does run at normal operating temp and the thermostat is not stuck open or something. As the others have said, O2 sensor is also a good guess.

If you do replace the O2 sensor the "upstream" one by the motor should be genuine Subaru, that's the one that will effect milage. The "downstream" one after the cat doesn't play a part in mileage, it's more of just a monitor, an aftermarket would be fine for it.

 

edit: You should do a search on the board for discussions on O2 sensors.

Edited September 21, 200916 yr by Suzam

There is no downstream O2 on a '92. There is only a single O2 for mixture control and I would also sugest you get an OEM one from the dealer.

 

GD

There is no downstream O2 on a '92. There is only a single O2 for mixture control and I would also sugest you get an OEM one from the dealer.

 

GD

 

Thanks for the catch on my info GD, I did't know that about the MY92 having only one.

 

Cars generally only had one O2 sensor until OBD2 came around.

Yes - the second O2 was mandated by the OBD-II laws - it's only purpose is to check the efficiency of the cat.

 

Incidentally, if you gut the cat you can cheat the O2 code by installing a spark-plug non-fouler between it and the exhaust - the sensor see's fewer HC's and doesn't set the OBD-II code for a bad cat (yes I've done this)

 

GD

I called the dealer and they want 160 plus tax prepaid, I see much cheaper alternatives online, is this dealer item worth it?

Buy a Bosch one for half the price it'll last just as long.