Recently purchased a 2003 ford ranger 4.0 sohc off a private dealer. Drove it around a good bit before I bought it and it ran fine, no obvious issues. Second day I had it it started and stalled twice. Then rough idle after I started it again, mellowed out after while. Then wouldn't fire at all. Cleaned MAF sensor and the cam position sensor since there was a code for that as well. Couldn't hear the fuel pump at all so I thought that might be it. Heard about fuel interia switch issues and tried resetting that and the truck started. Now when driving it runs fine until you get up on the throttle around 3,000 rpm and then it starts running hard as of its not getting enough fuel. Could it all be a result of the bad inertia switch or maybe a weak fuel pump as well?

 

I guess those could be the problem.
I don't know enough to really know.
Back in the day, I drove a Geo Metro.
Once, I got gas at a brand new gas station that just opened up.
On the way home, the car immediately started acting weird.
The car would not go over 20mph.
It wouldn't rev up.
The next day, it would start up Ok, but if I tried to rev it up, it would start to bog down.
I put some dry gas in it, changed the fuel filter, changed the plugs, and checked, and checked, and worked on it for a solid 2 days.
I was just about ready to light a match to the MF, and I tried one last time to rev it up. There was some life in it. It revved higher than before.
I put some more dry gas to it, and I only used high test for the next two tank fulls.
It ran OK after that.
It had some watered down gas in it.
I had heard about bad gas, but that was the first time I had ever experienced it.
I don't know if that's your problem, but check the obvious first.
Putting some high test gas in it, with some seafoam or dry gas, and replacing the fuel filter might do wonders.
Good luck.

 

Doesn't the dealer have some kind of warranty? Sounds like it is a fuel pump or fuel filter problem but there are a few things that could give similar symptoms.

 

Welcome to the forum Mirabella

Inertia switches ONLY need to be reset AFTER AN ACCIDENT, they can't just pop open and cut power to fuel pump.

So was this Ranger a rebuilt title, or salvaged title, whatever they call it in PA?

Inertia switch must be replace after an accident, reset button is there so vehicle can be moved, if possible, under its own power, to a safe location, it is not to be reused after a repair, because it will pop again, easily

So if button was up and you pushed it down and fuel pump started to work, get a new inertia switch.
And question private dealer to disclose what parts were damaged in the accident and replaced.
Because it was FOR SURE in an accident if inertia switch popped.

As for higher RPM/load and fading power, could be lowering fuel pressure when demand is high, so fuel filter or fuel pump.
2003 should have 65psi fuel pressure at idle, after shut off pressure should NOT drop below 55psi, is should hold pressure for a few MONTHS, not hours days or weeks, months and months, lol.

Restart engine and raise RPMs to 2,500, fuel pressure should stay above 60psi, if it is slowing dropping them could be filter or pump.

Clogged exhaust, if pieces if cat converter or muffler are flopping around inside, that can cause limited RPM and power, like running out of gas because you are, if air can't get out of the engine then air and fuel can't come in.
get a piece of wood or rubber mallet and tap on exhaust parts, listen for rattle of loose stuff