Okay so first off, i have a 4.0 OHV, i have 0 intake leaks , have thoroughly checked that. 02 sensor readings are that of good sensors, crank position sensor is new, cam position sensor/ synchronizer are new, fuel injectors are recently new, IAC is new and MAF is new. No i wasnt just throwing parts at it trying to fix it, the engine is actually from another ranger and when i swapped them i replaced a bunch of stuff that had aged while it was easiest but when I go to accelerate from a stop I get a gnarly hesitation that feels like the engine is about to stall then it runs perfectly after and no signs of problem until I stop again. Fuel trim looks normal until i accelerate and in high rpms goes all the way up to 20%. Do i have a cracked head or does anyone have any idea what else this could be? Will be testing fuel pressure tonight but I have a feeling it's not the pump. Thanks in advance and MERRY CHRISTMAS YALL!

 

STFT should go high when you accelerate

Assuming 1999 Ranger 4.0l
Does hesitation happen when engine is cold?
Does it happen only after warm up?
Does it happen any time, temp doesn't matter?

If you have Live Data look at the TPS(throttle sensor) reading
Closed throttle should be 16% to 19%, under 21% for sure, not 0%
% should go up INSTANTLY when you touch the gas pedal
(WOT, wide open throttle, should be 90%, not 100%, just FYI)

TPS gives the computer the "heads up" you want to accelerate, faster than MAF sensor can tell computer air flow is faster
TPS does what an accelerator pump did in a carb


EGR system
Unplug the vacuum hose on EGR valve and plug the hose, go for a drive see if hesitation goes away
EGR is ONLY USED after engine warms up

I assume there are no Codes or you would have mentioned those
Try a "sanity test" on the computer
Unplug one sensor, like the MAF, see if computer sets "MAF Circuit" code
Plug it back in
Unplug another sensor, same test
You are seeing if computer is recognizing problems

 

cant believe I forgot to mention i have lean codes on both banks, closed throttle is at 16% and 94% WOT and engine is the non egr version, but hesitation does seem to start after engine is warmed up a bit. Thanks so much for your quick response! Just looked at LTFT and its at 25% on one bank 23% on the other .

 

Key on, engine off
Does the TPS % change instantly when you press on gas pedal?
It should
Press it slowly and may sure % goes up steadily with no drops

1999 has a true Returnless Fuel system, 1998 to mid-2000, Ford dropped it because of issues
If possible test fuel pressure, 60psi is expected at idle
Then hold RPMs at 2,500(approx.) and should still be 60psi, if its steadily dropping or under 40psi generally, replace fuel pump assembly, this replace the fuel pump but also the fuel pressure regulator(FPR) thats on the assembly

 

Okay gotcha going to check both of those now. i rebuild automatic transmissions and have done quite a few top ends , but this one just had me puzzled so i greatly appreciate your expertise and assistance! Will let you know results in about 20 mins.

 

Okay so fuel pressure is about 53 ish at idle and drops to about 50 at 2500 rpm, tps voltage is smooth throughout the range but i noticed this time the voltage at rest was bouncing from 16.08% to 15.69% constantly, dont think that would do it but maybe? Also i could be mistaken but i believe this problem didnt start until i changed the Cam syncro but from everything ive read the ecu would default to the crank if anything and the reason i changed syncro was a cam position sensor code and the syncro had alot of play so better safe than sorry right?

 

Just unplug the CAM sensor and see how it drives, and make sure its sets a CAM circuit malfunction code, computer "sanity test"

And just a heads up, with OBD codes always look them up on a full list first, like this one: https://www.therangerstation.com/tec...II_codes.shtml

You will see several codes for one system/sensor, each meaning something slightly different
You can google codes after looking at the full list

Also in general, unplug and plug back in any and all connectors on sensors or anywhere you find them, this cleans off any build up of electrical corrosion and gives all the wires/contacts a better connection
All communications with the computer is electrical and most sensors operate on 5volts or less so small differences matter alot

In general 80% of sensors that are replaced were OK, just the unplugging and plugging back in is why the new one worked in place of the old one, the contacts were just dirty

My 1994 4.0l has all its original sensors, except O2s which do wear out after 12 years

 

yep computer is definitely sain, i now have p0171 p0174 which ive had and the new ones are p0340 and p1309 . Going to clean all the contacts of everything now and hope lol

 

Did it drive any better?

 

no sir , same problem as before unfortunately.