Fuel relay placement 1991 Buick LeSabre. Replaced pump & filter still won't start

The proper way to find the problem would be to pull a plug wire an see if it has spark or hook up a fuel pressure gauge an see if it has fuel pressure . Don't guess an just replace parts if you don't know how to test correctly .
https://www.youtube.com/watch?v=EB-hVxk4yus

check your fuel pump pressure sometimes after market parts are faulty

Is the pump getting power from the fuel pump relay ?

have u replaced fuel filters or checked fuel pump

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the fuel pumps circuit starts from the engines oil pressure sensor so replace that item next

ck if you have adequate fuel pressure 30-40 psi. if not it may need a fuel pump and filter replaced.

check your relay and your fuel filter should be replaced every 30,000 miles

You got a clean air filter? If it can't breathe, it won't run well or at all. Just like you. The car run okay until it's under load (driving)? If so, the fuel filter may be clogging. This will get worse till it won't hardly run due to no fuel. Fuel pump failing? The two cars I've dealt with that had clogged filters, would run less and less well under load, acclerate slower and slower and finally just die or not start. GM car, hmmmmmm. Fuel filter may be in engine compartment. I'm not sure on placement. My Tahoe's is on a frame rail but I think you have a unibody vehicle. If that's so, probably in engine compartment or it's tucked away somewhere. It's a canister looking thing with an in and an out for fuel. That's it. Not complicated just depends on placement as to how hard it's gonna be to access it. Fuel pump is a different story. In the gas tank, tank needs to be removed and pump replaced. Hope this helps.

fuel filter should be in the tank with the fuel pump.