Ford has used two fuel injection pressure, nothing to do with engine size

1997 and earlier used an FPR(fuel pressure regulator) with a Return fuel hose to the tank, spring in FPR was set for about 42pai
The returning fuel caused the fuel in the tank to warm up more so over time more emissions for EVAP system to suck up and lower MPG although not by much, lol.
These ran 35-45psi fuel pressure

In 1998 most Fords got Returnless fuel systems, no FPR, just one fuel line to the engine.
These ran 60-70psi fuel pressure
The computer would cycle fuel pump power off and on according to demand(RPMs and throttle position), and most had no fuel pressure sensor, for either 35psi or 65psi systems

On some models in the late 1990's/early 2000's you would find Check Valve/FPR in the Fuel filter.
It would be a 3 hose filter
2 hoses to the tank one to the engine.
The second hose to tank was the "return line" and had the check valve/FPR, set for 70psi.
I think this was only done on models where Ford had fuel tank "caps" that still had both hoses, so instead of throwing them out they just made a new fuel filter so they could be used.
Some Rangers did have this 3 hose filter


After making changes to system, i.e. new DPFE, O2s or ?? you need to drive it for at least a week, then reset codes and see if they come back

 

Doing some thinking about my motor setup and I'm wondering if having my fuel pressure regulator on same line with 2 other things could effect it at all. I did a lousy job of marking all the vacuum hoses and where they went when taking motor apart. she idle pretty smooth but maybe fpr needs its own vac source? I think its on with lines for heater, and egr...

 

Unless there is a leak in one of the other lines vacuum is vacuum, it isn't "used up" by sharing.

And FPR vacuum line is there to LOWER fuel pressure at idle when vacuum is highest, otherwise the spring in FPR is pushed open at about 42psi, the vacuum assists the spring pulling FPR open a bit to maintain about 30-35psi at idle

 

Ok, I got it somewhat..lol. Mine has a fpr on fuel rail on intake, pass side. the problem for mine as far as driving it for maybe a week is its not a daily use truck. so ill run it each day after work and take it for a 20 min spin each day. I want to start it on a cold wet morning as a test, I started it this morning, about 48 degrees or so, it idled about 800 rpm, for maybe 15 second, then up to 1,000 and idle smooth. ran good. it feels like it has a slight hesitation. but then takes off. I'm thinking about throttle body getting a good cleaning. then next wkend clear codes and see what happens..thanks again for your help

 

Something is wrong.

When you turn on the key on ANY fuel injected engine, its air valve(IAC Valve for Fords) will open all the way for starting the engine.
Cold, hot or medium engine temp doesn't matter, computer opens IAC valve full when key is turned on
Computer also checks ECT sensor for coolant temp, this is to set Choke mode it needed

IAC Valve being open all the way is why most fuel injected engines will surge when they start, without you touching the gas pedal, in fact you shouldn't touch gas pedal at all when starting, nothing bad will happen just not needed, and you do cause too much air to go into intake when you do.

So engine should surge, above 1,500 usually, when it starts and then RPMs will start to drop instantly as computer closes IAC valve to set "target" idle RPMs
Cold target is above 1,000 usually, the colder it is the higher
Warm engine restart can also be above 1,000 but will drop pretty fast to under 800

Cold start RPMs will start to drop fairly fast but won't hit under 800 for 5 to 8 minutes depending on outside temp and driving conditions

 

Ok, I understand, that's what my 95 saturn does. I'm kinda wondering if the 2 wires for ect go thru c115/ c124..that main engine to vehicle connector. Not all the wires are a match. I'm sure u know I had to move some around and even the manual didn't show every curcuit. I had a 88 ranger few yrs back and iac went, I put one in and she wouldn't idle for nothing, no code either. Could drive it but it wouldn't sit and idle. Turns out one wire had slid back in plug and no contact, once I pushed it forward she purred like kitten. This was like that for at least a mth and no code. I'm betting I got a cut or loose wire somewhere?

 

Ok I ordered the scanner tool, now I got to call bafx to find which apps they recommend. I had the iac valve off the truck today at work, sprayed it with fuel injection cleaner, plugged it in with it not bolted on to see if it did anything when my co worker turned key to run. it sounded like it made a little click noise but nothing moved. we wondered if we should have tried to start motor? anyway I'm thinking the reader/scanner tool is way to go.

 

IAC Valve should open all the way with key on, no reason to crank starter.
2 Wires should show 12v and ground on IAC

The computer will start to Pulse the Ground once engine is started to allow IAC Valve to close a bit so it can set cold or warm idle
12v(battery voltage) is constant.
But if you use sewing pins to pierce both wires to read voltage you won't "see" a pulsing ground, you would just see a lower voltage as computer sets idle.

IAC Valve is a spring loaded valve and motor/solenoid, when off the spring pushes valve closed all the way, when powered with 12volts the valve is pull open all the way against spring pressure.
As the computer pulses the Ground the valve closes with spring pressure, it is a very accurate way to control this type of valve.
My target warm idle is 625, manual trans, it is a consistent 623 to 628 every time I checked it


You will find most engine controls, even vehicle controls are Ground controls
Spark of course, always has been
Fuel injectors
IAC Valve
EVAP valve
EGR solenoid

Most of the lights are now relay controlled using Ground wire to activate relay

This makes for less 12volt wiring that could short out, a shorted Ground wire matters but usually won't start fires or melt wiring, lol.

 

Ok so I got a scanner from h/f...pretty nice. I noticed the maf reading is about 3.56 to 4.66 gps of air flow..is that a little low for a 5.0 even at idle?

 

Thanks, we'll the iac valve didn't do anything when I turned the key to run. I will b checking it more

 

That 4 gps MAF data is RPM specific, 5 liter engine should be closer to 5 gps if idle was around 750, i.e the 4.66 would be correct

It is also elevation sensitive, will read a bit lower every 1,000ft of elevation
And of course temperature sensitive, you will get higher readings with cooler air coming in past the MAF, heavier air, and lower reading as air temp increases, lighter air

You are reading direct MAF data, computer use IAT(air temp) sensor to compensate for that part.
The elevation is compensated for by the lower MAF gps reading

This is why there is no fixed number for MAF gps at fixed RPM, variables are there, most sensors are like this, so there are ranges that are expected.
Computer sets a code if a sensor is out of range

The MAF sensor gps number is checked with TPS(throttle position sensor) data and RPM
Computer knows it is running a 5 liter engine, so it can calculate gps acceptable range based on RPM and throttle position
There is actually a code for "MAF and TPS do not match"