1993 Explorer 4.0 auto. Has lots of guts when it runs. Symptoms: Starts immediately; can burn rubber out of the driveway; after a few minutes, it engine starts to die upon acceleration, at first at full pedal, then closer to no pedal, then stumbles but will remain in idle but won't move car when put in gear -- misfires and dies with slightest pedal depression. When engine is shut off and restarted, problem immediately disappears and runs great for the nest few minutes, then the problem reocurrs. Actions already taken: replaced Mass Flow unit and fuel regulator; replaced electrolytic capacitors in ECM; loosened gas filler cap to relieve vacuum; fuel filter was replaced about a year ago. O2 sensors are questionable. Vacuum system is tight, no hissing or noticeable leaks. Plugs are recent and not fouled when pulled and checked. Expert local mechanic says fuel pump is good and produces required pressure, although he measured it with engine cold, not up to temp. Pump was replaced 4 years ago. Problem does not seem to fluctuate with engine temperature, but with passage of time. The time until problem occurs has reduced from 40 minutes a week ago to 4 minutes today. A real head scratcher! What else is left to test? I'm told fuel pumps don't fail this way, nor do fuel filters -- that is, varying with an amount of time. Wrong, maybe? I'm out of ideas. How about you gentlemen? Thanks/Regards/Jim

 

Welcome to the forum

Not sure who would have told you that about fuel filters????
Fuel filters fail exactly that way AND so can fuel pumps, although fuel pumps tend to just quit one day and strand you

Simply a matter of fuel volume
If an engine needs 6 gallons of gasoline an hour at 60MPH
And fuel filter can only pass 4 gal/hour then you will start to run out of gas in that hour
At lower speeds/RPMs engine doesn't need that 6 gal/hr

You need to get/rent a fuel pressure gauge, put it on the fuel rail
Start engine and you should see 30-40psi at idle
Raise RPMs to about 2,500 and hold it there, if pressure starts to drop you have a volume problem.
Doesn't matter when filter was last changed, if you got some "junk" in the tank it can fill up pretty quick.
There is also a "sock filter" in the gas tank to filter out larger bits, that is usually changed with the pump............but not always

Restarting allows down time so filter can pass more fuel thru, but the reoccurrence of the lack of power would come back faster than if it sat longer.
From your description it reads like the longer it sits the longer it will run at higher load/speed

On the 1993 Fuel Rail is also the Fuel Pressure Regulator(FPR), fuel pump can produce about 75psi pressure, same volume just higher pressure.
The FPR has a valve and spring inside set for 45psi, so if pressure at injectors gets to 45psi the valve is pushed open and fuel flows back to tank, until it is 44psi, then spring pushes it closed again, 40-45psi is spec for FPR spring
FPR has a vacuum hose attached, this pulls the valve open at about 35psi, when idling, high vacuum
Then when you step on the gas vacuum drops and FPR closes so fuel pressure goes up..........BUT demand for fuel is higher(you stepped on the gas) so it averages out and pressure stays between 30-40 psi

Your FPR could have a weak or broken spring.
With fuel pressure gauge in place, turn key on and off several time, like 6 times, fuel pressure will go up each time but should top out around 45psi.
And it should hold that pressure for MONTHS, not hours, days or even weeks, it will hold MONTHS and MONTHS

If FPR is leaking or not holding 40psi then its the same as clogged filter, 1/2 your fuel is flowing back to the gas tank thru the FPR so you "run out of gas" under load.


Clogged exhaust
Long shot from description but not a no shot
No 4-stroke engine runs well with any back pressure(its a myth), if exhaust system gets partial blockage then back pressure builds up and it feels just like "running out of gas" because that is whats happening.
If exhaust can't get out then new air/fuel mix can't get in.
Vacuum gauge can tell you if this is happening
Or just put your hand over tail pipe and have someone REV the engine, you will feel exhaust flow change or....not change when it should
This could be heat related as exhaust components get hotter and metal expands and loose parts shift around

 

What has my attention from your post is the fact you opened up the computer and replaced the capacitors.

I assume these are surface mounted capacitors on a multilayered PCB.

What caused you to suspect and replace these capacitors?

Did you replace them with the same value capacitors?

Did you obtain the new capacitors from a trust worthy source?

Many suppliers of capacitors, surface mounted or radial type that the general public can get have become dinosaurs because of the throw away society we have become.

This means the inventory in these supplier's warehouses are getting old.

Did you just go through the PCB replacing all the capacitors or did you use a on the board cap checker to confirm if the caps you replaced were in fact bad.

Did you use a cleaner to remove any trace of the leaking electrolytic off the PCB?

Did you double and triple check for lifted circuit paths?

My gut is telling me that you may have separation of the multilayered PCB or a missed cold solder joint or perhaps you were sold capacitors that have exceeded their shelf life and were not reformed.

Regardless if the computer was a problem or not at the beginning of your quest to repair this problem your having.

I suspect all of some of your problem may still be in the computer, to me it sounds like a connection issue.

I doubt new old stock capacitors is the problem especially if you didn't have a problem soldering them in place.

I am interested in what you have to say, since I have not communicated with another person that repairs anything at the circuit level since my brother passed away many years ago.

It has been many years since I did this type of work myself, my eye sight is not what it used to be nor is the steadiness of my hands because of my neck and back problems.

Yet I used to love to repair electronics, My brother and I specialized in Audio and video. Anything I know I learned from my brother whom was professionally trained.

So it is safe to say I am no expert.

All of my questions are to help me eliminate your computer from the equation these questions are not meant to question your ability or skills.