I have a 98' Ranger with a 4.0L ( 2 wd ). When you put it in drive, it has no power, and if you accelerate the gas, it has a severe hesitation. Once, up to speed, it'll smooth out until you mash on the throttle. Then it hesitates really bad again until you get out of the throttle. I replaced the coil pack thinking it was a misfire. Last night I installed a new throttle position sensor and still same problem. I need to scan it for codes once the check engine light comes back on. Any suggestions?

 

Could possibly be your transmission going out as well.

 

Damn. It was rebuilt awhile back. Its been some years but only like 20k or 30k miles ago

 

I would think MAF(mass air flow) sensor is your problem, common issue on 4.0l and Rangers in general.

Good read here: Ford Ranger Mass Air Flow Cleaning, Removal and Installation

MAF sensor is the main sensor used by computer to set the air/fuel mix.
It is a pretty simple device, a wire is heated, as air flows passed the wire it is cooled, the amount of cooling tells computer the amount of air coming into engine.
Computer also has an air temp sensor(IAT) to compensate for outside air temp and cooling of MAF wire.
Over time the MAF wire can get a coating on it, it acts like an insulation on the wire so actual air flow data is incorrect.

Good news is that these are very easy to clean, don't use Carb Cleaner, MAF Cleaner or other electronics cleaners are OK.

The MAF sensor is on the air cleaner housing, there is a large Plenum(air tube) connecting MAF to Intake Manifold, if that plenum is cracked or its gaskets are leaking then MAF data would also be incorrect.

 

Ive cleaned the MAF before, but not recently. Friend of mine told me to unplug it while the truck was running to see if it would change and also try driving it. Nothing. It acted the same way. Should I still clean it or replace it?

 

how long since you replaced the fuel filter on your ranger

 

I replaced the fuel filter last year, but its only been maybe 6K miles ago. With having 4 cars and a GSX-r in the driveway, I can spread the mileage.

I picked up a code reader on the way home since I was pretty sure the check engine light would come on now.

PO340 - Camshaft position sensor.

 

The CPS controls sequential fuel injection and aids in spark advance so could cause a hesitation, the fuel injectors firing early or late can do that
And P0340 usually means CPS magnets have come loose, common issue in late '90s 4.0l CPS
It is generally a good idea to replace the whole assembly as the bushings on the syncro shaft tend to fail at around 80k miles.

Not sure what year they changed over, it was around late '98, but they used a 3 wire CPS and then switched to a 2 wire CPS.
These are two different kinds of sensors, so it isn't just "one less wire", lol.
Make sure you get the same one so your computer can understand it.

There is also an alignment tool needed to reinstall, some parts store will have loaners.
Ford part number is: 303-529 – 96~98 4.0L OHV Explorer/Ranger/Aerostar (3-wire HE)
Or OTC 6472 – 96~98 4.0L OHV Explorer/Ranger/Aerostar (3-wire HE)

You can try it without the tool
Rotate engine manually so TDC is at 0deg mark
Mark location/direction of old CPS rotor, take pictures
remove and reinstall new CPS in same orientation.

As you lift old assembly out you will see it rotate, the gears are angled, orient new assemble rotor the same as the old one after it is out, as you slide new one in it will rotate to correct position, hopefully.