Oxygen sensor

Hi, all

I had my Metro for 8 years, its an 89 model with 202,600 miles on it and still running good. However, recently I noticed a big reduction in gas milage (it's got down to 28 MPG). The compression is good. I believe it is a bad oxygen sensor. But when I disconnected it, the check engine light never came on. Any ideas why? Where is no point of replacing the sensor until this mystery is resolved. Please help!
Thank you

Hi, all

I had my Metro for 8 years, its an 89 model with 202,600 miles on it and still running good. However, recently I noticed a big reduction in gas milage (it's got down to 28 MPG). The compression is good. I believe it is a bad oxygen sensor. But when I disconnected it, the check engine light never came on. Any ideas why? Where is no point of replacing the sensor until this mystery is resolved. Please help!
Thank you

Are you certain of the light operating period? Does it illuminate when your turn the power on and extinguish on start up?

O2 sensor replacement is a good start however I would not stop there. I would replace the ECU temp sensor ans well as the intake temp sensor. Neither of these should be confused with the temp gauge sender.

O2 sensors are 30k tune up parts and should be changed. $25
ECU sender $15
Intake air Sender $19
Fuel pressure regulator diaphram $23
New thermostat $6

The intake and ECU sensors are vital tune up parts as the tell the computer how much fuel the engine needs and control ignition timing. Fuel pressure diaphrams get stiff (harden) and slowly cause fuel pressure variances. Changing those parts will certainly make your engine run better, but if your Catalyst is plugging nothing but changing the Cat will help.

Blake

DieInterim where do you get those parts so cheap. i got a 1997 geo metro 1.3 4 cylinder and the check engine soon light came on and had it checked and it said the intake air temp sensor was bad. so i changed it and reset the puter and it came back on after about 15 miles. i did find a vacum hose off behind the throttle body but cannot find any place it goes. i was getting 39 mpg before the light came on, but now only 30. i just bought this used a couple of months ago and he said the engine only had about 20k on it. runs good but cammot get that light off to get better milage. any suggestions.
thanks

DieInterim where do you get those parts so cheap. i got a 1997 geo metro 1.3 4 cylinder and the check engine soon light came on and had it checked and it said the intake air temp sensor was bad. so i changed it and reset the puter and it came back on after about 15 miles. i did find a vacum hose off behind the throttle body but cannot find any place it goes. i was getting 39 mpg before the light came on, but now only 30. i just bought this used a couple of months ago and he said the engine only had about 20k on it. runs good but cammot get that light off to get better milage. any suggestions.
thanks

Cost Less auto parts in Vancouver WA.