Ranger 3.0 fuel pressure problem. Need help please.
 

I have a 2003 Ranger edge 3.0 flex fuel 183,000 miles. I have been having a misfire problem, only at idle, always cylinder 3. Replaced the fuel filter. Just replaced fuel pump assembly. With the old pump my fuel pressure was 49psi key on engine off, and running at idle it was 59psi with a shaky needle. With the new pump, when I turn the key on it jumps to 60psi then imedietly drops to 49psi, when the pump shuts off. Running it is at 60psi with steady needle. Koeo the pressure holds good at 49psi but does slowy decrease, about 5psi in 15 minutes. What would be causing the pressure to drop to 49psi? I am checking pressure at the fuel rail. Pressure according to the haynes manual should be 60-65psi koeo and the same while running at idle.

Welcome to FTE.

It's just a thought, but I would check the fuel pressure regulator.

The regulator is part of the assembly I replaced.

Now for the bad news. If you used an Airtex fuel pump module that could be your problem. The hose that goes from the return to the pressure regulator needs a clamp on it if it didn't come with one. I have had a lot of problems with that brand of pumps on the rangers here at work. I hope this helps you out some.

I used a Delphi. Could that hose still be an issue?

With the mileage on this ride, your having replaced the fuel pump & still a cyl 3 misfire code, then the rough idle, fuel pressure leaking down/falling off after shutting the engine down, maybe put a leaky #3 cyl fuel injector on your suspect list.

Use your stethoscope, or rig one from a broom handle, long screwdriver, length of tubing, or rubber hose, one end to the suspect, the other to your ear to try & determine if #3 injector sounds different than the others.

If you come to suspect the #3 fuel injector has a runny nose, before replacing it, or removing for cleaning, maybe consider trying a 20 oz dose of Chevron Techron Concentrate Plus in the tank at the pump before filling up (so you get good mixing) & fill up with Chevron, Texaco, Caltex, or now Shell, as those fuels already have some PEA in their ad pack, so the additional 20oz dose of Techron will raise the treat rate 10X over pump gas alone & will usually get the tidy up job done in one tank. Run most of the treated tank out before refilling, or treating the second tank if you think it needs another dose.
More thoughts for consideration, let us know what you find.

Thanks for the suggestions. I was thinking it may be a leaking injector, since its always the same cylinder misfire that I get on the cel. I just wasn't sure how to check if it was leaking. I did listen to it with a screwdriver and could hear it working. I will let you know when I figure it out. Thanks again and I'm open to any more ideas until I get it fixed.

Did the #3 injector sound different that the others????

It did sound different. Sounded like it was clicking slower than the other ones. Also I disconnected the electrical connector while it was running at idle and didn't notice any change in the idle. Im just going to replace that injector. I'll let you know if that fixes it.

Several things could cause a problem with #3 injector. Before replacing the injector, check its resistance. It should be between 12 & 16 ohms. All of the injectors resistance values should be very closely matched within that range. So measure all injectors resistance with your multimeter & if you do replace #3, make sure the replacements resistance value is closely matched with those in the vehicle.

If the injector checks out ok, at KOEO measure B+ voltage at its electrical connector to make sure its getting full B+ to operate. Then back probe the B+ connection with the engine running, to make sure you have full B+ under the load that the injectors coil puts on its circuit.

If that's ok make sure the computer #3 ground switching driver is doing its thing, as excessive electrical resistance causing a voltage drop to the injector, or excessive inline resistance between the injector & the ground switching driver will corrupt things.

Ok. I'll check that as soon as I get a chance. Probably tomorrow morning.

With the idle not changing when you disconnected the #3 fuel injector electrical connector, it kinda sounds like it has a runny noise & is leaking enough to keep #3 cyl running well enough not to affect idle rpm much.

It's your money, but if the injectors electrical resistance checks out, I'd maybe first try the Techron treatment & see if it'll make a difference. It's a lot less expensive than a new fuel injector. If the injectors have never been cleaned, the Techron could make a noticeable difference in driveability & could improve mpg by tweaking all the injectors spray pattern. It'll also tidy up the intake valves, piston crowns & combustion chambers of deposits. The autoparts stores have been running it on a bogo deal lately, so it would be $6 & change for one bottle & if that didn't do it, the other one would likely finish the job.

OR, just remove the injector & try cleaning it. Let us know how it goes.

I checked the resistance on the injectors. They were 12.3-12.6 ohms. The voltage at the connectors was 12.06-12.11 volts with koeo. I also replaced the #3 injector and it made no difference. The fuel pressure still drops off. I still need to check the other things you mentioned. Just thought I'd give you an update.

OK, good feedback on the injectors resistance value range.

What's the new injectors resistance value in ohms & did it sound the same as the old one???? Was the old fuel injectors tip wet with fuel & or dirty/varnish/carbon, around its tip????

Edit: After replacing the #3 fuel injector & erasing the misfire code, do you still have the rough idle & misfire code returning for #3 cyl??? With the mileage on these injectors, you could have more than one injector with a runny nose!!!! Keep us posted on your KOER voltage drop reading for #3 injector.

The voltage at the connector while running was 13.7 volts. The resistance on the old injector was 11.99 ohms. The tip looked good. Still get the same rough idle and cylinder 3 misfire code. If another injector is leaking could it cause cylinder 3 to misfire? I have never had any other code come up, always cylinder 3 misfire. My code reader can show live data, if that would help. I dont know what to look for on there. Fuel pressure is still low with koeo. I'm really lost on this one. I may have to just take it to the dealer for diagnostics. I can usually fix things myself, but this ones got me stumped.