On my 2003 2.3L I have had this issue for a while where I am driving the truck for a while and then park it, go in to a store for a few minutes, then come out and it won't start. I have verified that it is a fuel delivery issue and not a spark issue because I can pull off the air intake hose, spray some carb cleaner in the throttle body, then it will start and run fine for about 3-4 seconds. After a 10-30 minutes it will start again and run fine for days or weeks. I have never had it happen cold. At first I thought it was a fuel pump issue and it always seemed to happen when the tank was low on gas (Thought maybe a crack in a hose on the fuel pump assembly). But then I randomly replaced the fuel pump relay just to see if it would help and suddenly I didn't have the problem again for months. Then last week it happened again and I had a nearly full tank.

From looking at the service manual, it appears that when the key is on, all that has to happen is the ECU grounds pin 2 on the fuel pump relay and the fuel pump relay contacts will close. This will pass power on to the inertial fuel shutoff switch, which then sends the power on to the fuel pump (assuming inertial fuel shutoff switch has not been tripped). All of this is relatively simple and I have a multi-meter and some test leads that will allow me to test all of these the next time it happens. But it all starts with the ECU grounding pin 2 on the fuel pump relay (pin 80 on the ECU). Does anyone know what goes in to the decision to the ECU grounding that pin? In other words, what conditions cause the ECU to ground that pin. I can't seem to find this information in the service manual. I would assume not much has to happens (as far as sensor data to the ECU) because the fuel pump will turn on as soon as you turn on the key, even before the engine is running.

Thanks for any insight.

 

The Computer(PCM) grounds the Fuel Pump relay for 2 seconds each time it boots up, but only for 2 seconds
So you can turn key on and then off and then on again and fuel pump will run 2 seconds each time key is turned on

Cranking speed of engine with starter motor is 200rpm

PCM will ground fuel pump relay full time when RPMs are above 350-400rpm, engine started

This is a safety feature, in an accident if fuel line should break you don't want an electric fuel pump to keep running, so if fuel line breaks engine would stall(run out of gas), and drop under 350rpm, so PCM ungrounds the relay to shut off the pump
Yes the inertia switch is there for that as well, so there are two shut offs

The 2 second run time is to Prime the system for startup, but it only adds about 10psi fuel pressure, 1998 and up ranger run at 55psi pressure, so you can try to cycle the key on and off a few times before trying to start, maybe build up lost pressure in the system.

You can hook up a test light to the inertia switch, so you can see if it lights up or not when you have this issue, and just a heads up, when key is on engine off, after the 2 second closing of relay you will see 5-8volts on the fuel pump power wire, it has no amps just volts, this is the Monitor circuit in the PCM to see if fuel pump is getting 12v when relay closes
If it doesn't then PCM should set a code, "secondary circuit" problem


TPS(throttle position sensor) can cause what you describe
All fuel injection computers have a "clear flooded engine" routine
It allows you to crank the engine with spark on and fuel injectors OFF

TPS sends computer under 1volt with throttle closed and 4.5-4.9volts with throttle wide open

With key on
Engine at 0 RPMs
Throttle at 4.5volts
Computer will shut off injectors

So key on
Press gas pedal to the floor and hold it down
Crank engine over
It should not start, it should not fire at all, no fuel

I use this every morning to pump oil thru the engine before starting

As soon as you release gas pedal computer starts injectors again

So..........if TPS was sending computer 4.5v............then no start, and it would start by manually adding fuel
This could be TPS issue OR wiring for TPS
TPS has a 5volt wire from computer, if that wire could contact the Signal wire(1v-4.5v) then that wire would have 5v and computer would shut off injectors at start up

Although I would expect running issues and a code or two if this was happening while engine was running because TPS is use for throttle position, lol

 

Thanks RonD! There is a lot of information in your post and I'm still trying to digest it all. But one thing you said:

>PCM will ground fuel pump relay full time when RPMs are above 350-400rpm, engine started

Makes me wonder if it is the CKP sensor. If the PCM doesn't know the RPMs are above 350-400rpm, then it won't turn on the relay for the fuel pump. But I assume that no CKP sensor signal would also cause no spark. I've assumed that I have spark since the carb cleaner spray will make it run for a few seconds. Is that a valid assumption?

 

The CKP(crank sensor) also times Spark for startup, so engine wouldn't have started adding fuel manually to the intake, so not CKP issue

 

That is a good point. I have been carrying around my OBD2 reader and other tools in the car now so that when/if it happens again I will be able to determine what the problem is. I checked the TPS and like you said it goes from about 0.8V to 4.5V when I checked it. Also I did the WOT start, and like you said it doesn't start. Thanks for that information as well, I wasn't aware of that function.

When it happens again and I figure out what it is, I will post back here.

 

Mine did that several times but eventually start.Then it totally failed and I had it towed in.They reset the inertia switch located on the inside of the fire wall. It ran fine for awhile then it would trip randomly again.The last time I had to hold the red button down and turn key at the same time to get it to start.I researched cost online then called the local Ford Dealership and the part was the same price as online.Replaced the switch and haven't had the oroblem for about 4 month now.You might check it next time it fails to start.There is YouTubes on it. Ron is the Ranger Wizard though.Mine didn't have any dash problem light, when it failed.

 

Yeah, I knew these could trip easily, but since I had mine start again even though I didn't press the button made me believe it wasn't the problem. I have all of the tools with me to check out:

1. Is the fuel pump relay getting the signal from the PCM
2. Is the relay functioning when it does get the PCM signal (i.e. is it passing voltage on to the intertia switch)
3. Is the intertia switch tripped/failing
4. TPS output
5. Fuel pressure

Thanks.

 

If the engine starts by adding fuel manually then you know the fuel injectors are either not opening to let fuel in or there is no fuel to let in, those are about the only two options


You can simply push in the pin on the fuel pressure test port to see if there is pressure/fuel at the engine, be CAREFUL, gasoline and hot exhaust systems don't react well to each other, you should have at least 25psi pressure, 55psi running, and that can spray a long ways

If there is no pressure/fuel then you found the problem
If there is pressure/fuel then you know injectors are off-line