2000 Geo Prizm Codes?

[bedlam]

Venturi , thanks for the reply to my previous post concerning the plate light. I am more than happy to make a post to the "fix post". I cant seem to find how to get there tho.I might be a bit blind..lol can you tell me where it is located?
Also I could sure use some help with my 2000 Geo Prizm. the engine service light is on, still runs, I bought a OBD and have the following generic codes.

P0171 System too Lean (Bank 1)

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1) (pending)

The engine is a four cylinder with auto. about 27,ooo miles on the engine.
I have cleared the code with the OBD only to have it come back after a short trip running the car.
Hopefully, these codes will ring a bell with someone who can hopefully tell me some of the things that can be causing it.
Let me add, that the engine is a "junk yard" repalcement. And when I installed it it ran fine without the light on for some time.The orginal engine started to burn oil and eventually spun a bearing.My one thought is that it may have to do with all the oil that would have passed past the O2 sensors.As they weren't replaced when I did the motor.There are two O2 sensors , and they are a bit pricey for me. And with my luck Id replace the wrong one. Its a 50/50 guess unless one of these codes points to which one.
Again Thanks.
Allan

[way2old]

The "fix post" is just your follow up on your thread when you make a repair. As for the codes, P0171 usually indicates a vacuum leak somewhere. This will cause the P0420 and P0421 you are getting. I usually deal in Fords so this is kinda strange to me, but they all work on the same principal. P0420 will trip due to ignition concerns, fuel pressure, exhaust leaks, and air intake concerns along with vacuum leaks. Sorry I can't be more specific on it. Does your vehicle run a MAF sensor? If it does look at the baro readings in hertz and see if it is reading correctly. We are at about 100 ft and our normal baro here is around 153 to 157 hertz as a reference. Maybe one of the guys that deal in different vehicles will drop in and help more.

[bedlam]

Thanks for the info on the vacum leak, Ill check it out.Maybe it is the simple things... fingers crossed lol
I have been known to go for the serious diag. only to find I should look at the simplist thing first.
Always open for anyone elses thoughts also.
Again thanks.
Allan

[DanD]

Sorry I won’t be of much help either not for any specifics anywise; the last year my service manuals show a Geo is 97. I guess that’s when they stopped selling them here in Canada.
It very well may be what you said that the front O2 (pre converter) is dead from all the oil that the old engine has past by it.
If so that would set the 420 code because the ECM compares pre and post converter O2’s to determine converter efficiency.
Dan.

[bedlam]

OH I think your right. It is considered a Chevrolet. I get it confused, seeing as they were make by Toyota that year. And I am right to think that the sensor couldnt be cleaned?I dd consider buying as new front one. I just felt it would be a 50 50 chance.
Thanks for your input tho.
Maybe ill get some other ideas as well.
I have an friend who may be able to put it on a more expensive test machine. Perhaps that would give more firm idea as to what is wrong.
Thanks again....Allan