1996 Blazer 4x4 Trouble: Lacking Power and p0133

1996 Blazer LT 4x4 4.3L v6 135,000m

The code is p0133 for o2 sensor.. (lazy sensor, bank1, sensor1).

Would like to know which sensor is the correct one to replace.From what I have read, this one is supposed to be on the drivers side. I just took a look and I can see one sensor pretty much right underneath my drivers seat about a foot down from where my exhaust connects to the engine...and on passengers side there are two others before my cat.

First I'll start out by saying I got what I THOUGHT was a great vehicle about 6 months ago from a dealership. Ran great for maybe 4 months, then I noticed a lack of power/ bad gas mileage! (felt like it was running about 80% of the norm ). Could smell it running hot, so I had the radiator flushed out which looked like it had never been done before to me :/ and I changed the fuel filter, and ran some fuel injector cleaner through a tank of fuel.

This helped big time for close to a month and half, then I could smell the engine running hot again and felt the lack of power (again running about 80%). Radiator cap wasn't holding pressure ( was only a few months old) so I put a new one on, and it would let just a small amount of my coolant seep out once the engine warmed up. Did a test for combustion gas in my coolant, and it was a negative. Did the radiator flush myself this time (dipsticks at jiffy lube didn't even put the correct amount of coolant in), and had a tranny service done. Again, this seemed to help for about a week, then **** really hit the fan.

Engine power felt like it was running at MAYBE 50-60%, would have to downshift it out of overdrive to get up small hills on highway very sluggish acceleration..was just brutal. Took out all the plugs and changed them. The plugs looked like the engine was running just a little lean..except the one in the back left cylinder was worse than the rest. After doing this it took me back up to about 70-80% power.

The smell persisted, I replaced the thermostat to make sure it wasn't sticking at all. Flushed radiator AGAIN.

Now, the truck is up and down as far as the power goes..One minute it will seem like its maybe running 80-90% of the norm..and the next it will drop down to maybe 70%. Also sometimes when I accel from a complete stop, I can hear a metal on metal clunk noise very briefly...tranny?

P0133 Popped on again last night (I knew it would since I didn't replace the part the first time about 1000 miles ago)

I am guessing that as a result of my o2 sensor being "lazy" im getting a bad fuel/air mixture and that is whats been causing causing my lack of power...Maybe Jiffy messed up my tranny fluid level(wouldnt surprise me). Would it make that much of a difference if they put too much fluid in?

Trying to sell this thing so I can move, can't sell if it aint running well!! Any help is appreciated.

P0133 O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)

I believe it is the sensor closest to the exhaust manifold ( upstream ). And it could cause sluggishness, loss of power.

When buying used you need to be very careful who you trust. Better to get it from a Dealership ( ie: GM, FORD OR CHRYSLER ). They do a better job fixing up & checking the vehicle for resale.

Too much fluid can cause pressure issues.

Metal on metal clunk noise could be coming from the Tranny.

Replacing the O2 sensor will probably give you the power back ( fix the problem ).

You should also check fluid levels ( engine oil, tranmission fluid, coolant ) to see if high or low ( & fix them ).

Bank 1=side with cylinder#1(driver's side on 4.3L)
Sensor 1=upstream sensor(closest to engine)