Okay so I appreciate any help I can get on this I have a 2001 Ford ranger 4.0 l and when I started up in the morning it seems to run decent being that it's in a open loop and it's getting more fuel. But what's happening is if I floor it even when it's cold it hesitates once it reaches higher RPMs now once the truck warms up I lose power to where I almost can't drive it it never dies on me and it starts up and idles perfectly drives down the road perfectly in the morning but taking it home from work acts like it has no power and we'll just bog down on me to where I have to pull over let it sit and then start it back up to make it home. I believe it's a vacuum leak I let it warm up pull the IAC and it did nothing I've changed the PCV tube I've changed the EGR valve I've changed the DPFE I've changed the purge canister I've checked the cats I've changed the fuel filter I've checked the fuel pressure I've changed the spark plugs I've changed one side of the injectors and nothing makes a difference. I have sprayed brake cleaner or starting fluid around the whole motor and never heard it change RPMs one bit I got a po171 bank 1 sensor and that's the only code my next guess would be maybe a lower intake gasket but if anybody can give me some insight so I don't have to take it to a shop I would muchly appreciate it guys

 

Welcome to the forum

Reads like either you are losing fuel pressure, dirty fuel filter or weak pump OR..............you have clogged exhaust

Install the fuel pressure gauge, raise RPMs to 2,500approx. and hold it there, pressure should stay the same, if its slowly dropping you found the problem

Install vacuum gauge on the intake port, start engine, 18-21" of vacuum is expected
Raise RPMs to 2,500approx. and hold, vacuum will drop of course, and then climb back up and hold steady, if its slowing dropping you have clogged exhaust
Blip test, at idle manually open throttle all the way, vacuum should drop to 0-2", then let throttle snap back closed, vacuum should jump above 21" instantly, if its slow to return, clogged exhaust

 

Hey thanks for you response.. I have had the exhaust from the exhaust manifolds all the way back to the muffler off and inspected so I'm 100% sure it's not the exhaust I will try the fuel pressure and get back to you on what it says I don't have a vacuum gauge but I plan on picking one up tomorrow

 

Vacuum gauge is a good tool to have

A Gasoline engine is a self powered "air pump", and best way to diagnose a "pump" issue is to watch its pressure
Good read on tests to run here: https://www.gregsengine.com/using-a-vacuum-gauge.html