Last week my engine put out a code 45-O2 rich code out of the blue. I did a data log and it was stuck at 1.065 volts so I replaced the sensor. New sensor is doing the same thing. If I reset the code it works fine for a few minutes then goes back to the code 45- 1.65 volts thing. It's a heated sensor and has power going to the heater OK. Everything else seems to be "normal" as it was before the sensor started acting up. Did I get a new bad sensor or is this a sign of something else that I'm missing?
I don't get it.

 

probably something else you're missing.

check the o2 sensor wires, make sure none have melted on your header/manifold, shorted out, etc; if the output wire was shorted to +12v (such as on the heater power wire) you'd get that effect;

if you let the car get cold, turn the key on, (ignition/motor OFF); and then measure the voltage on the o2 pin at the ECM, what do you get?

any changes to the motor? if you have a vacuum-referenced fuel pressure regulator (like a TPI does), if it wasn't getting vacuum it'd be running at higher pressure and that might send you too rich too.

 

I checked the O2 heater voltage at the sensor plug and it was good. I didn't see any melted wires but didn't trace them far back. I'll do that! I don't think it's actually running rich, the BLM and INT are within a couple points of 128. I hooked up my wide band this morning and ran it untill the error came up and it never got richer than maybe 14:1 once the choke/mixture was off. Up to that point the O2 was switching rich/lean as I would expect (closed loop)but out of the blue it goes to 1.065 and stays there.........
Only recent change to the engine is I solved a overheating issue I had for a long time so it runs much cooler now but temps don't get low enough for a code 15- low coolant temp.....Fuel pressure is normal too..........

 

Mine was doing the samething, but only
in open loop. I changed and checked everything
with no luck. I had a old ECM I installed it everything
worked fine, I swithched back and the problem
returned, so in my case it was the ECM, it was only
2 years old

 

I have a spare ECM, I'll try that too.
Thanks.

 

Any testing done yet

 

I haven't had a chance. This isn't my DD and I've been sooooo busy with work and more.....
I will swap it out probably tomorrow evening and report back.

 

It's not the ECM. I put my spare in with my old chips and when I started it, it never left 1.065 O2 volts. Warmed up into closed loop and a few seconds later came a code.
Good news is it seems to be more consistant now which will help troubleshooting.
I still need to thouroughly check the wireing like 91L98Z28 suggested.
Thanks for the ideas guys, we'll get to the bottom of this!

 

Next time it goes high unplug the O2 sensor from the harness. If the wiring and ECM are OK the data logger will show about 451 mV.

Silicone poisoned sensors report rich (high voltage) to the point the engine shuts off.

RBob.

 

OK I did this and it seems the O2 is bad again. Also checked the wires good and everything seems fine. I don't know if I bought a bad sensor or if something is causing them to go bad. What condition may possibly cause this?
Does anyone have a part number for a good quality 3 wire O2 I could get from NAPA or the like? The one I'm replacing came from Summit and is labeled as a Holley if that matters.
Thanks guys.

 

Go straight to the general, do not pass go, do not collect $200.

GM Delco AFS-74 is what you want.

https://www.thirdgen.org/forums/diy-...sensor-ok.html

if indeed you're suffering a silicone poisoned sensor, well, any silicone used anywhere near the sensor can kill it. there was a post here some time ago, I forget who made it, but they had used silicone at the other end of the garage, and it wasn't sensor safe variety, and they killed their o2 sensor. I guess they are really hyper sensitive to silicone.

 

Thank you, I'll get that sensor and try it....I haven't used any silicon so I don't think that's it.

 

Well I put in a new delco sensor and it seems to be working fine so far. I only run it in the driveway for about 15 minutes. If it acts up again I'll report back.
Thanks for the help all!!