Adjustable Fuel Pressure Regulator Questions

[NeverStock]

My 94 4.0 recently developed a dead spot at full throttle which most people fixed by replacing the FPR. I would like to add an adjustable regulator however it seems I would have some problems hooking up to the fuel rail due to how the stock FPR mounts to it also the stock FPR does not have a return line and I'm not sure where to plumb an aftermarket line to. Does anyone know anything about that?

 

[fastpakr]

Can you elaborate a bit more on the original problem?

 

[Dirtman]

Yea I'm a bit confused why you want an adjustable pressure regulator. You can't change the factory fuel pressure so what benefits are you trying to gain over a OEM regulator?

And what do you mean by a dead spot?

 

[NeverStock]

towards the end of the throttle I lose almost all power and it starts to misfire it switches suddenly too there isn't any gradual decline I've checked most of the vacuum system and replaced the tps

 

[Dirtman]

Sounds more like a clogged exhaust, clogged fuel filter or fuel pump issue not a regulator issue.

 

[NeverStock]

Sounds more like a clogged exhaust, clogged fuel filter or fuel pump issue not a regulator issue.

I have replaced the fuel filter and my exhaust is getting full flow

 

[NeverStock]

Yea I'm a bit confused why you want an adjustable pressure regulator. You can't change the factory fuel pressure so what benefits are you trying to gain over a OEM regulator?

And what do you mean by a dead spot?

The benefits would be if I ever made any more mods to the fuel system and wanted more pressure then I wouldn't have waisted my money on 2 regs. it is also cheaper and looks cool even if it serves no benefit currently

 

[fastpakr]

Test your fuel pressure and post the results.

 

[NeverStock]

Test your fuel pressure and post the results.

Will do but I'm going to have to rent a tester

 

[Dirtman]

The benefits would be if I ever made any more mods to the fuel system and wanted more pressure then I wouldn't have waisted my money on 2 regs. it is also cheaper and looks cool even if it serves no benefit currently

The ECU uses a set and known fuel pressure for calculations. There is no sensor for fuel pressure, the computer simply knows the system runs at 35psi and bases injector timing off of that. Even if you do "mods" that would require more fuel you would only need to change the injector size not the regulator. Without completely changing to a stand alone programmable ECU system you cannot change the fuel pressure from its set factory spec 35psi.

 

[NeverStock]

The ECU uses a set and known fuel pressure for calculations. There is no sensor for fuel pressure, the computer simply knows the system runs at 35psi and bases injector timing off of that. Even if you do "mods" that would require more fuel you would only need to change the injector size not the regulator. Without completely changing to a stand alone programmable ECU system you cannot change the fuel pressure from its set factory spec 35psi.

and I suppose there is also no way to tune the stock ecu is there

 

[Dirtman]

and I suppose there is also no way to tune the stock ecu is there

Eh... kinda sorta not really. Ford EEC-IV computers are not very sophisticated so they cannot be tuned like a more modern EEC-V computer. You would need to see if you can find a local tuner shop and see if they can fiddle with those older systems. Most only work on obd2 systems though. But outside of supercharging it, the system can run happily on 35psi. Even with a supercharger most people run the stock pressure. Injector size and timing matters more than pressure.

 

[RonD]

The FPR on 1997 and earlier Rangers has the Return Line attached to it, and a vacuum line, the vacuum line is what regulates engine Load fuel pressure

The IN fuel line from the filter attaches directly to the Fuel rail, on a 4.0l OHV that's the part between upper and lower intakes

The stock FPR's internal spring is set for 42-44PSI
This is what pressure should show with no vacuum hose attached
With hose attach and engine at idle, vacuum is HIGH so that pulls FPR open a bit more reducing fuel pressure to 35psi, approx.
When you accelerate fuel demand goes UP and Vacuum goes DOWN, this helps stabilize pressure at 35psi
Same for engine Load, which is directly related to Vacuum in the intake, light load high vacuum, high load low vacuum

So pretty simple system
Without this Vacuum adjustment the computer has a hard time calculating OPEN TIME for the injectors, so you can get the stumbling when going from low load to high load
Say pressure is 43psi and low load(no vacuum hose attached)
When you accelerate, fuel flow increases and pressure drops to 30psi, or less, so computer's calculated 43psi injector open time is WRONG, so it has to increase open time for lower pressure, and it does, but YOU feel that as a stumble, no instant throttle response because fuel pressure is not Stable

Adjustable pressure is what there is with stock system, in working condition, it adjust to engine load which is what you want

Higher fuel pressure doesn't give any engine more power, fuel injected or carb
Gasoline engines need 14.7:1 air:fuel mix
Adding more fuel gets you a flooded engine, not more power


TPS(throttle position sensor) this is used by the computer to give instant throttle response
Its a 5volt sensor, like most
Works like a light dimmer or volume control, variable voltage/resistor
Computer "sees"
0.9volt closed throttle
4.5volt wide open throttle

If there is a dead spot, at say 1/2 throttle where voltage drops suddenly then there would be a hesitation as computer "thinks" you took your foot off the gas pedal and turns OFF the fuel injectors
Very very rare failure

One of the fuel saving benefits of fuel injection is that the computer can turn OFF all the fuel injectors when your foot is off the gas pedal when coasting, carbs just kept on sucking in fuel, lol
Computer turns injectors back on when RPMs are under 1,500 or so
It does intermittently turn on injectors to keep Cats hot when coasting