96 4.0 low fuel pressure can't find cause

[Sadfordguy]

I have a 96 explorer sport 4.0 will not idle correctly at all, at idle in neutral it will start choking for a few seconds like it's running out of fuel then it will pick up and idle smoothly for a few seconds before starting to choke up again like a constant cycle of nearly dying then being fine. In gear it will stall when it starts choking. Fuel pressure holds steady at 27 psi with FPR connected to vacuum and 35 without( but doesn't idle any better). I have replaced dpfe and EGR valve, fuel pressure regulator, fuel pump, fuel filter, IAC, upper intake gaskets, O2 sensors, camshaft position sensor, injectors, cleaned the MAF, sprayed the entire intake system down with carb cleaner and didn't notice any uptick in the idle. Checked vacuum on gauge and holds steady at 15hg ( according to the gauge I used it was good). I have verified the pump is getting power. I even took it to a shop and they couldn't figure it out, granted they weren't Ford specialists. Please any help or ideas to check out would be amazing, I'm about half tempted to light it on fire at this point

 

[EB4X]

Were any of the replacement parts you listed done BEFORE this situation / symptoms occurred ?? ....(and your putting on list for our sake on what's new / newer parts to rule out)
EDIT: Yes, your fuel pressure on your year should be at 29 - 31 with vacuum connected to regulator....although on low end....not sure if 27 would conclusively indicate that's your issue.

 

[J_C]

Agreed, while 27 PSI is too low, it should manifest more at higher throttle, as observed when you disconnected the vac line.

When you did that, was the vac line just sucking in air to make it lean or did you plug the line? Gotta plug the line...

Did you use a decent brand fuel pump? I would measure the voltage at the connector, make sure a bad connection or frayed wire, etc isn't causing voltage drop to underpower the pump, since it should peak above 35 PSI without the regulator doing it's thing, but as already mentioned it may not be the primary problem.

Something I would try briefly is run it a minute (is that long enough to get the bad idle condition?) without the belt on, in case a belt driven component is bogging it down, and I'd check pulleys for resistance turning and wobble, and after running without the alternator spinning to charge the battery, I'd hook a battery charger up to recover battery charge.

I don't know if 15hg vac is good enough. It might be but is a little low for some engines, so I would look around for potential vac leaks, lines off or potentially intake manifold gasket leak. I noticed you did replace the upper intake gasket, but like EB4X I wonder how much of what you list happened just before the onset of the problem.

There is the dilemma, how much work to do at once because it's convenient, versus doing so much at once that if there is a problem, it's harder to determine what went wrong. Anyway, sometimes an intake manifold gasket needs some time to settle in and will need retorqued, especially with plastic manifolds where the torque spec was conservative to not break it.

I did notice you mentioned spraying the intake with carb cleaner so some of the above may not apply but similarly look at all vac lines going anywhere. You can disconnect and plug them off to see if that helps, better at the manifold than at the end of the vac line so if there is a break in it, it doesn't interfere with determining it isn't the cause.

If all else fails, sometimes you can get a shop to diagnose it for the hourly rate then DIY repair it... beats lighting it on fire. Just have an agreement with a different shop that you aren't paying a diagnostic fee for an "I don't know/couldn't-replicate" type of useless diagnosis.

 

[96eb96]

I have a 96 explorer sport 4.0 will not idle correctly at all, at idle in neutral it will start choking for a few seconds like it's running out of fuel then it will pick up and idle smoothly for a few seconds before starting to choke up again like a constant cycle of nearly dying then being fine. In gear it will stall when it starts choking. Fuel pressure holds steady at 27 psi with FPR connected to vacuum and 35 without( but doesn't idle any better). I have replaced dpfe and EGR valve, fuel pressure regulator, fuel pump, fuel filter, IAC, upper intake gaskets, O2 sensors, camshaft position sensor, injectors, cleaned the MAF, sprayed the entire intake system down with carb cleaner and didn't notice any uptick in the idle. Checked vacuum on gauge and holds steady at 15hg ( according to the gauge I used it was good). I have verified the pump is getting power. I even took it to a shop and they couldn't figure it out, granted they weren't Ford specialists. Please any help or ideas to check out would be amazing, I'm about half tempted to light it on fire at this point

That is a lot of parts thrown at it.
These usually run very well. Can you get Forscan software and an adapter? Or even some other scan tool.
Need to know:
Long and short fuel trim at idle, 1500, 2500 RPM. This will check health of the fuel pump and any vacuum leaks.
Baro reading (should read 159Hz at sea level (corresponds to a pressure reading), it reads actual barometric pressure at your altitude - different a bit from the weather report). This checks MAF health and possible exhaust blockage
Misfire data for the cylinders (forscan reads out this information). These engines are prone to small head cracks, there are easy solutions that could work if that is the case.
EGR flow voltage at idle and cruise (probably that system is ok because you changed everything). Should be 1 volt at idle (closed).
The fuel trims at idle will reveal any vacuum leaks, but you can also close off all vac ports (including evap line on the tb) to verify. There are also vacuum connections to the HVAC and 4x4 system (a ball thing by the passenger wheel).