As the subject says, just replaced the sensor and now it won't start. Its flooding the engine when I try to start it, but why? I had LH2.4 Code 2-3-1 before replacing the sensor and it was idling rough and losing power while driving. The O2 sensor was completely covered in soot when I removed it. Very nasty.

I'm going to try to troubleshoot this more after dinner but I thought I'd post and see if anyone's had this problem in the past.
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92 745T 127K; 83 242Ti 188K - Brick on blocks for now.

Thanks all for your help. I actually had this fixed last week but I had National Guard duty again so I didn't have a chance to post back before now.

My problem turned out to be a mix of things. The FPR appears to be fine but there was a vacuum leak so I replaced that hose.

I had made some adjustments to the throttle body to keep my idle level up when my IAC quit working. This caused the TPS to be nonfunctional. Essentially I just jacked the idle up to keep the car running and it was fine until I replaced the O2 Sensor. The idle was smooth and everything until shortly before I changed the sensor. Also, somehow the TPS had gotten unplugged..??? I don't know how long this had been undone or how it got that way but it was unplugged when I started tearing stuff apart under the hood.

Everything is back together now and its running nicely and boosting strong. Just the way I like it. Thanks to all who helped me with this.
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92 745T 128K; 83 242Ti 188K - Brick on blocks for now.

limphome mode.
fixed rpm-sensitive fuel mapping. no closed circuit mixture control.

Thanks. Good suggestion. I took a lot of things apart today and did a lot of cleaning and little things that needed to be done for a long time. I had a bit of a PCV problem and so I cleaned that entire system out today, replaced the distro seals, etc. Once everything is back together properly (I hope) I'll see whether it starts or not. If it still won't start, I will try unplugging the AMM to see if it will start and run poorly rather than not running at all. Thanks again.
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92 745T 128K; 83 242Ti 188K - Brick on blocks for now.

Just from experience..The O2 screws in. Was your cable free and allowed to twist free before you plugged it in?? What computer do you have?? My guess is that you shorted out the computer.

Yes the cables were completely free while I was threading it in.
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92 745T 128K; 83 242Ti 188K - Brick on blocks for now.

Did you use a stock replacement or aftermarket??? If you used the aftermarket and crossed the wires you could have run power back to the computer on the ground circuit.

Remember.... Computers run on smoke. The electricity keeps the smoke in. If the smoke gets out.................OhOh!
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1965 Mustang A block 4 speed, 1969 Cougar Eliminator, 1990 Super-Charged Thunderbird and a car (740) that my wife can drive!!!

Slyfox. Yeah I knew about the smoke. I think its still in there. The Sensor I used was a direct fit ($$) replacement. I've been patching little drivability problems for the past few months and now I've partially fixed the root cause and I have to undo all my band-aids if you know what I mean. Anyway, I haven't had a chance to work on it since Friday night but hopefully tomorrow or the next day I'll get it going. I'll post back with my results good or bad.

Thanks again.
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92 745T 128K; 83 242Ti 188K - Brick on blocks for now.

The oxygen sensor, whatever it's condition, won't cause a no-start.
I'd look at the fuel pressure regulator(see the FAQ) for a leaky diaphragm.

I just pulled the vacuum line off of the FPR and there was fuel evident on the "dry" side of the diaphragm and the hose smelled of fuel although there was no fuel puddled in it per se.
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92 745T 128K; 83 242Ti 188K - Brick on blocks for now.

Thanks. That was the next area that I was going to check out.

The car started and ran before I changed the sensor. That's why I'm confused. I think I'll go unplug it and see if it starts w/out the O2S. If no luck there, I'll check out the FPR.
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92 745T 127K; 83 242Ti 188K - Brick on blocks for now.

crank the motor at wide open throttle to initiate flood clearing(no fuel delivery)