No fuel pressure

[A/Cmark]

I have a 1998 ranger with a 4.0 .. I was driving home and out of the blue the truck seemed like it was running out of gas with a half TANK.
the fuel relay is fine , the inertia switch is made and has voltage .
I jacked up the bed and fed 12 volts to the pump and it worked.
I used piercing leeds and found the pump runs for a couple of seconds then power is cut. every time I turn on the key it powers the same time.
I thought the fuel pump sensor ( on pump assembly ) was bad replaced and truck is the same
I have a obd2 to usb interface but I don't know what I am looking for.
I used to work at a corvette shop, and now work with computer automated controls on refrigeration systems.
I just don't know what tell the ecm there is a need for fuel , or what may be acting in safety mode

PLEASE HELP

 

[alwaysFlOoReD]

There are others that are better at diagnostics and I hope they will chime in.
The fuel system turns on the fuel pump for two seconds, and if the computer doesn't sense 500[?] rpm or more the fuel pump won't stay on. It could be that the fuel pump isn't delivering enough pressure and/or volume. You need to test that. I believe it should be at 65 psi for your year but could be wrong.

 

[RonD]

Ford computer will only activate fuel pump for 2 seconds when key is turned on, it won't get power again until engine RPMs are above 400.

This is a safety feature, if fuel line should break or accident fails to trigger inertia switch when engine stops or drops below 400rpm fuel pump power would be cut off via Fuel Pump relay.

Fuel Pump relay's coil gets 12volts with key on, but coil has no local Ground, that wire goes to the Computer, computer grounds coil for 2 seconds(sending fuel pump Fuse power to inertia switch) then waits for engine to start, or if you key off and on it will run for another 2 seconds.

Check fuel pump fuse in engine fuse box.
Swap Fuel Pump relay and WOT(wide open throttle) relay, they are the same relay part.
WOT relay cuts off AC compressor at full throttle so won't effect regular driving.

Did you check the fuel pumps ground wire at the tank?
It is often grounded in the cab near inertia switch but could be a frame ground.

Yes, like alwaysfloored said, fuel pressure in '98 should be 65psi at the rail, and it should hold that pressure for a few months, not minutes, hours, days or weeks,............months

This is a Returness system, so pressure is held by Check Valve in the fuel pump, basically just a flap that it pushed open when pump is on and closes when pump is off to hold pressure in the system.
Turning key on and off a few times should build up 45 psi of pressure, you get 10-15psi when pump runs for 2 seconds.

On some returnless systems the fuel filter will have a "return line", look at the fuel filter, if it has 2 lines from tank and 1 line out to engine it does have a return line, and I believe there is a pressure valve in there as well.

 

[A/Cmark]

I never saw the fuel pressure over 3 psig
how does the ecm detect rpm ?
and yes I changed relay checked all fuses
For the slight instant the pump runs it has good ground

 

[RonD]

Fuel injected engines with distributor use that to send RPM to computer, distributorless engines use Crank Position sensor.

But that won't matter in your case, 3 PSI means pump isn't even pumping, if system is at 0psi it should jump up to at least 15psi first time pump runs for 2 seconds, and then hold there, if you cycle the key again then it should jump to 30psi, after 30psi it would usually only jump 10psi each time because of pressure already in the system.

Reads like fuel pump is bad, could be a broken line in the tank but thats a longshot

You could use a jumper in fuel pump relay slot to turn fuel pump on full time and see what pressure it could build up

Look here at relay slots: http://www.blackmilkmedia.com/automotive-5-pin-relay-wiring-diagram/

1st or 3rd diagram

85 and 86 slots are the coil hook up, power passing thru here magnetizes core and closes relay

30 will be 12volt power from the fuel pump fuse, 87 will be the slot with the wire to inertia switch.
It can be visa versa, doesn't matter really for this bypass.

So you want to put jumper from 30 to 87

87a isn't used in this, 30 and 87a are connected when relay is OFF, 30 and 87 are connected when relay is ON

 

[kimcrwbr1]

If your saying the fuel pressure doesnt rise over 3psi when you cycle the ignition switch on, try disconnecting the fuel line at the fuel rail and put the fuel line in a jar and cycle power. If you get good fuel flow (volume) replace the regulator and see if it holds pressure after cycling power. The pump creates flow and the regulator creates pressure.

 

[alwaysFlOoReD]

Does the returnless style use a fuel pressure regulator?

Sent from my XT1032 using Tapatalk

 

[Milton]

No. Here is a good overview of return less fuel injection systems. It's not specific to Ford/Rangers.
http://www.aa1car.com/library/returnless_efi.htm

 

[Mark_88]

No. Here is a good overview of return less fuel injection systems. It's not specific to Ford/Rangers.
http://www.aa1car.com/library/returnless_efi.htm

Good article...thanks!

 

[A/Cmark]

Ladies gentlemen and all creatures fortunate enough to drive a ranger

DO NOT BE A GENUIS / IDIOT LIKE MYSELF

I am a master ref tech who deals with computer automated refrigeration system (yes the most complex ) I have been training techs in my field for over twenty years. The two main things I drill into there soft sculls is
#1 KISS rule =keep it simple stupid
#2 don't overthink problems
You know like going over every circuit and relay, while thinking if the pump makes noise it is pumping.
Another neat discovery was no fuel pressure at gauge while truck purring like a kitten.My beloved harbor freight sold me a gauge with a locked bourden tube.

Today is my birthday, my truck runs like a champ. If I could get my girlfriend to stop complaining I would think I am in heaven.

I hope I can be a help in the future on this site, for now I am Genius/idiot and am happy I am not in denial .

Drive safe .