igintion timing

I just replaced a blown intake manifold gasket on my 96 s-10. It has a 4.3 vortec. After I was done I started it to make sure it has no leaks. It ran good for about an hour. I then shut it off and came back to restart it the next day. Now it wont even start and when it cranks over it back fires and the engine seems like it is missing. Dont understand y I worked on day but then not the next. I hooked my code reader to it and it is telling me all my senors are not ready and I have a ignition misfire problem. The truck has been sitting for about 7 months prior to me replacing the intake manifold gasket.

I just replaced a blown intake manifold gasket on my 96 s-10. It has a 4.3 vortec. After I was done I started it to make sure it has no leaks. It ran good for about an hour. I then shut it off and came back to restart it the next day. Now it wont even start and when it cranks over it back fires and the engine seems like it is missing. Dont understand y I worked on day but then not the next. I hooked my code reader to it and it is telling me all my senors are not ready and I have a ignition misfire problem. The truck has been sitting for about 7 months prior to me replacing the intake manifold gasket.

did you mess with the distributor?