I have a 99 olds Bravada. I replaced fuel filter Saturday. Still wouldn't let it start. Left it overnight. Yesterday it started right up n no issues all day. This morning it wont start again. Ideas

You will likely need to replace the fuel pump inside the fuel tank.

When you changed your fuel pump, did you also change the filter?
Also, I had 4 pumps go out in 1 year on a truck I had. It was a crappy pump. Remember you get what you pat for.. Got the name brand and didn't have any more problems.. Also, look for a loose or pinched wire, had that happen too.
Good Luck!

you pulled the ignition switch and installed a different switch
that means that you have installed a different immobilizer system
try reprogramming the new key to your ECM and it will probably go

Check the plugs and see if they have fuel on them if not check the catalytic converter it could be plugged and putting back pressure on the engine and not allowing the fuel into the cylinders. Can you spray fuel into the throttle body and get it to run. If so you may have a fuel pump problem or fuel filter issue. I am betting on the cat. you can pull the o2 sensor ahead of the cat and the engine should run if it is plugged. It will run rough but at least it should start.

When was last tune up? Plugs, wires, all fluids & filters especially fuel filter? I'd start there and run a good fuel system cleaner through it. Also avoid cheap fuel - lot of questionable fuel at cheap/cut rate stations.

The request doesn't say what the problem is...takes extra time to start?

Sounds like fuel-related - injectors/fuel pump/fuel filter? Is there a strong fuel smell or black exhaust for a few seconds/minutes after starting it when it's sat overnight? If so, then you've got a leak causing excessive fuel...kind like 'flooding' the engine on old cars w/Carbs.

It could also be the temp. sensor. If it thinks the car is 'warm' it won't give the car enought fuel to start when cold.

GL,
Td

REPLACE THE FUEL FILTER AND CHECK THE SPARK PLUG CONDITION, IS SOUNDS LIKE YOUR FILTER IS OLD AND PLUGGED OR IT GOT FLOODED DUE TO OLD SPARK PLUGS

Aftermarket fuel pump failure? Try "thepartsladi" store on eBay for low price GM OEM parts. Could also be wiring harness to fuel pump.

i would say that rack and pinion steering unit is going out or is weak

Take a rubber hammer beat on the fuel tank if it starts it is the fuel . My bravada did the same thing and it was the fuel pump in the tank