Hi guys,

I have an 03 Explorer that had a starting issue. Long story short, it had no fuel pressure. So after testing the relay, I switched out the pump with an Airtex unit . All seemed fine...for a while.

Became hard to start again, checked schrader valve with key on, and not running, no pressure. Strange though, it would run.

So got the fuel pressure gauge on it. Turn the key and pressure will go to about 5-10psi and then drop to zero. Turn key off and on again, up to 5-10psi, then drop to zero. Turn key to start and pressure goes up to 10psi, then starts, then goes to 30 while running and you can drive it around. Shut off motor and pressure goes down to zero.

Can you guys help me understand how the sending unit is suposed to hold fuel pressure and not release it? Is there some kind of check valve in the sending unit assembly that can be cleaned or does it need a whole sending unit with another pump? I already spent the $100 for the pump, and it is working if you can drive it!

 

Airtex is junk, they act like old worn out OEM units right from day 1. Been through enough of them on my own vehicles to know that. For the record, did you replace the fuel filter yet?

Buy a Motorcraft fuel pump. They are only a few brands that work correctly, Motorcraft, Carter, and Walbro are good ones, AC Delco is another good one. Pretty much everything else is garbage.

 

Yes, a new fuel filter is installed. How does the pump hold the line pressure? Or is there a check valve in the return line? I know there is a fuel loop to the fuel filter, than a single line up to the injectors. I am thinking there must be some form of a check valve in the end of the return line to keep the pressure up while the pump is not running? I can hear the pump shut off after about two seconds when you first turn the key and pressurize the fuel rail.

I do have the same Airtex pump in my F-150, and been performing flawlessly for quite a few years.

 

The check valve is inside the pump.

 

Gotcha. Shouldn't there be another check valve on the other end of the fuel loop?

There is a black thingamajig on the end of the return line that slides up and down on one the shafts of the sending unit, then the fuel return comes out of that. If this is also a check valve, then I think this is the problem since I replaced the fuel pump and it went from not running to running, but dropping pressure on the line.

See here at Rockauto.

 

Check for a fuel pressure regulator.

 

03 does not have a pressure regulator. It is a return type fuel system.

 

Do you mean it's a returnLESS type system? From my experience with Hondas and Fords that have regulators (91 to 97 model years), the regulator dumps fuel back to return to maintain the fuel pressure. I thought these were referred to as "return type" fuel systems. If there is a return line, then there needs to be some device (restriction) to maintain pressure at the right level. Otherwise, the pump won't develop any pressure, unless the return line itself is so small to be the restriction.

If the fuel pressure line is dead-ended (no return), I would think some way to regulate pressure would still be required. Maybe there's a relief valve or pressure regulator built into the fuel pump assembly? I would take apart the old fuel pump and see what's inside. That's just me though. I do that with most failed parts.

I thought at one point, Ford abandoned the returnless type fuel system because it was problematic. Have you checked for TSBs related to the fuel system?

If you're serious about fixing this yourself, I would get the Ford service manual. There's no substitute for having the correct documentation. Otherwise, you're likely to get people like me who are just throwing out wild (fill in the blank) guesses.

Can you post pictures of your old fuel pump showing the black thingamajig or describe its location on the Delphi image?

 

I found this diagram here: http://www.justanswer.com/ford/2lyer...fuel-pump.html

There's no return line mentioned in the item descriptions below the image. But, I think you're really after a good schematic to find out what components are in the system that could be causing your issue.

If pressure isn't maintained when the pump is off, I would think it's a bad check valve or a leaky injector(s).

 

Mikeman, you're correct. If there is no return line, the system is a returnless system. In that case, either the PCM or a Fuel Pump Driver Module provides a Pulse Width Modulation (PWM) signal to the fuel pump to increase or decrease the pump duty cycle. This is conceptually similar to how the PCM controls the fuel injectors, using a pulse width and duty cycle to control how much fuel enters the air/fuel ratio.

According to the factory service manual for the 2003 Explorer:

The fuel pump assembly consists of:

• the electric fuel pump which provides pressurized fuel to the engine.
• the fuel level sensor.
• the fuel pump inlet filter (filter sock).
• a check valve which maintains system pressure after the pump is shut off.
• a parallel pressure relief valve (with bleed port) which maintains fuel in the system after the fuel pump is shut off.
• a fuel pump driver module (FPDM) that controls the fuel pump based on input received from the powertrain control module (PCM).

-Rod

 

I will be replacing the sending unit next week. Based on the above, I am sure it is the parallel pressure relief valve in the sending unit. Sounds like the check valve is in the fuel pump body, and I would think that the parallel pressure relief valve is the black thingamajig with a return line in the top and a dump line into the bottom of the tank. Will keep you all updated on the result.

 

On the 03 it uses the fuel filter as the end of the loop. So two fuel lines come into one side of the filter, and on the other side of the filter, a single line goes to the injectors. I imagine they use a return system only to the filter?

 

It has a damper on the right fuel rail. I took mine out and it was full of dirt

 

Just wanted to update this thread. It was the PPRV not holding pressure. You could almost blow into the line and get it to release. Using my airhose, I could just begin to put some pressure on it and it would release air down through its exit tube.

Moral of the story. Replace the whole sending unit, not just the pump, unless you have a way to test it first. I used a Delphi sending unit and it seems to be working fine. The gas gauge may be a little off compared to the original.