4.0 l bogs down after 15 to 20 minutes of driving if key off for 2 minutes will drive another 15

[CallMeSyd]

Thanks that I could do. What exactly would I be looking for? Air in excess with the fuel trims going wacky or a very low reading? The odd is that it always idles fine and if I put it in park when it is happening the engine will rev up with no load so if one of the sensors is bad I would think that the condition would carry over both in park or in drive.

You need to watch your fuel trims yes but anything out of the ordinary. Any sensor not reading properly, and watch it while driving when it's happening or if you see any values stop, drop off, or become erratic under load. Sorry I'm on my way to a doctor's appointment I'll try and remember to get back to this.

 

[Explorer Jeff]

2002 XLS has got me puzzled 200k miles 4.0L
Starts well idles great
No codes
Hot here over 100F
Drives fine for 15 to 20 minutes and then acts like a minibike with the choke on. Lacks almost all power but still will idle perfectly. Also out of gear engine will rev up. When you key off for a couple of minutes it will go for another 15 -20 minutes before the same thing will happen. If you lay into the gas when it is happing it will spit and sputter a little but I am thinking I may be hitting the wot cutout when pushing the gas trying to get something out of it.

So far I have
Searched all the forums I could find
Cats have been replaced (most common cause found for lack of power)
Fuel Filter replaced
Fuel Pump is new and running at 68psi
checked for vacuum leaks and found none

With Forscan I checked
MAF voltage - good across the range with the reference numbers I could find
TPS voltage- good across the range with the reference numbers I could find
Pulled cleaned and tested the EGR - was not dirty and used hand vacuum to check movement
Pulled and cleaned IAC since i was there but it Idles great
ECT in forescan matches the temp gage and is running in the middle
It is not happening in the transition open and closed loop as I made sure it was closed before and still the same
Fuel trims look ordinary within a few percent of 0

initial thought was it was temperature related but with the 2 min key off the engine only gets hotter from the short soak.

All ideas or insights would be appreciated

Had this problem in a 2004 XLT 4.0L and found that an OBD2 freeze frame after the engine was goofing off revealed a 70psi fuel pressure, when it’s supposed to be 40psi…
The system works in these trucks by monitoring fuel pressure… The fuel pump can supply 70psi but the engine only needs 40psi, and if it goes over that the fuel pressure sensor (attached to the fuel rail underneath the drivers side of the plastic intake manifold) tells the fuel pump to slow down or shut off until the engine uses up the excess, at which time the pumps starts pumping again…
MY fuel pressure sensor was sticking at the 70psi pressure (telling the fuel pump to shut off) and not returning to its “zero” (unpressurized state)… basically it was sticking and worn out (@120k mi)…
My guess is your fuel pressure sensor is sticking in various positions rather than at wide open like mine was, but is tired and worn out anyway!
Replace it and enjoy! FYI, to get to the sensor you have to remove a few things, which is a great opportunity to clean the throttle body and reclaim some gas mileage, do a reset on your ECU when you’re all done and do a learn sequence for your idle and driving style and you’re good!!!

 

[410Fortune]

Not sure if the 2002 has a fuel pump pressure sensor or a fuel pump driver module
Pretty sure that didn’t come into play until 04-05

 

[Explorer Jeff]

Not sure if the 2002 has a fuel pump pressure sensor or a fuel pump driver module
Pretty sure that didn’t come into play until 04-05

I think you’re right, didn’t know precisely myself and thought it was an older design, but it was used on Explorers from 2004-2010 (and to 2012 on Ford Escape)…
Ford Part #: CM5229 (3F2Z9G756AC)
(Bosch made these for Ford)