89 Buick 3.3L engine won't start

Hello.
My 89 Buick is having some starting problems. I just put in a new fuel pump, plugs,wires,starter. It will crank then backfires through the intake. It will also crank normal for a few seconds then slow down for a second then crank normally again. When it slows down, thays when it backfires through the intake. I would really like my car to run again. Please help.

Hello.
My 89 Buick is having some starting problems. I just put in a new fuel pump, plugs,wires,starter. It will crank then backfires through the intake. It will also crank normal for a few seconds then slow down for a second then crank normally again. When it slows down, thays when it backfires through the intake. I would really like my car to run again. Please help.
Welcome to AF, when did this problem start, info missing here, after the work was done? If so, recheck the plug wires are where they should be. If not post back.

before and after I fixed the fuel pump.

Make sure you have good compression, then disconect the maf, if so equipped, then try it and post back results.

It has good compression. I also had problems with the maf. It used to be disconnected and still had the same problem. I use to use starter fluid to start the engine.

Start from scratch, check fuel pressure, get a noid lite, make sure all the injectors pulse, scan it and check for cranking rpms, will it start and run now with carb cleaner in the intake?

I know all the injectors work and it has fuel pressure. It is also cranking normally. It still does it. It won't start. It just backfires through the intake. If I open the intake, a big flame spits out.