[V8] Help!! It doesn't run anymore.

[Tony and Lillie]

I am in the process of working on a '90 V8 that ran and doesn't anymore. I replaced the center diff on it. Before I put the exhaust all back together, I wanted to make sure it worked. The car had no O2 sensor hooked up (no X-pipe). It was running rich(slight smoking), but not terribly, maybe 10% richer than normal. Anyhow, on the test drive about 1/2 mile from home, it quit and wouldn't restart. While trying to start, it floods itself out immediately, and starts to "lock up" as if it is preigniting. The only way to stop it is to take out the fuel pump relay and run it clear, but it still won't start. It has great spark, new plugs, and obviously has fuel. 
One other curious thing - After trying to start it for about 30 secs with a normal tach signal, the tach starts going crazy. It bounces between 1 and 3 K RPM's. What the heck is going on?
We also had the distributors out, but they are back in and aligned correctly. The car did run great before we started, and also right up untill it died. Therefore I have ruled out firing order and distributor order. 
Could we have killed something by running it without the O2 sensor? Or maybe............?

Tony Hoffman