I have been having problems with my O2 sensor hot getting hot enough. I installed a 3 wire O2 sensor but it only preheat to 399. I've tried 2 different sensors, same problem
I've got headers, a free flowing thrush muffler and open pipes the rest of the way out.
Anyone else have this problem?

First test to do might be to find out how many amps it should use and then measure how many it's pulling. I actually don't know how hot they are supposed to get. I never had problems with a heated O2 sensor with long tubes. How did you wire it?

According to my tunerpro data logs the O2 has to hit 500°f to become "ready". Both my heated ones only preheat to 399ish then climb to around 430ish. That's still too low and keeps kicking an error code 13.
I have the power drawing off the MAF power wire and the ground to a chassis ground stud I installed that's connected to the engine block ground strap and to the negative battery cable.

Where is the sensor located or how far from the cylinder head? In stock configuration they came with a non-heated sensor so I'm hesitant to say your codes are because of the sensor itself

Where are you getting the sensor temperature from?

Also as Tuned Performance is pointing out, code 13 is not to do with sensor temperature, but a circuit problem usually, and low activity will sometimes set it.

The sensor is in The "stock" location. Roughly 12 inches from where the 2 legs come together.
the temperature is coming from the "converter temperature" reading in tunerpro RT.
So do think I should check wiring next? I got a new sensor figuring maybe it fouled when the car was running like garbage before but the new sensor does the same exact thing.
The main reason I was wondering about the temperature is because Tunerpro doesn't see the sensor as "ready" until 450-500. If the car runs 5-10 minutes with the o2 sensor as "not ready" it kicks code 13

The "temperature" in TP is simply a calculation, not actual temperature. I don't know how it derives this number but it's useless IMO.

Yes, check the wiring, especially the signal wire.

Oh. Ok thank you I will do that

Stock a '91 doesn't have a MAF, did you mean the MAP sensor? If so that is only a 5 volt feed.

RBob.

This question was about my other car, my 86 Camaro not my signature Firebird.
I found the problem last night. When I installed the 3 wire O2 I apparently forgot st solder the signal wire. Both the power and ground wires were soldered which makes it weird.
after soldering the signal wire too it works fantastic, I didn't even make it out of the garage before the O2 sensor was "ready"
Thank you everyone