Sunday, January 16, 2011
In most modern vehicles the electrical pump is not exposed at any fuel level except absolutely empty. It's located in a "fuel delivery module" (FDM) which houses the pump in an enclosed plastic reservoir. The pump output not needed for fuel delivery is redirected to power a venturi jet pump which draws in gas from the tank regardless of fuel level. This jet pump keeps the reservoir completely full most of the time, and the flow used to power it maintains consistent fuel flow through the electrical pump in times of low demand to maintain cooling. The reservoir is only drawn down during the few moments before pump pressure drops below the threshold needed to keep the engine running. Even then, there is still some flow through the pump, it just sucks enough air to prevent it from pushing it all the way to the injectors.
This is also what keeps your engine running if you go around a corner quickly, or up a steep hill, when the tank is low. The bulk of the fuel sloshes to the back or side, but what is trapped in the FDM continues to provide fuel until a more normal attitude is restored.
Another common one I see on the internet is "don't run it down because it will suck in stuff from the bottom of the tank" but that FDM reservoir intake is pressed against the bottom of the tank - in fact, it is spring-loaded to insure it is ALWAYS pressed hard against the bottom of the tank. In other words, it always draws from the bottom, regardless of fuel level. There is a mesh cloth filter (usually called a "sock")on the jet pump inlet to catch any crud, and often a screen on the bottom of the electrical pump as well.
If you are really interested for some reason, googling "fuel delivery module" will bring up diagrams of how it's all put together. The general design is fairly universal across manufacturers.
That being said, there are those who feel that when you run your tank low on fuel, your fuel pump may not be covered by the fuel. That can cause the fuel pump to overheat and that can lead to early fuel pump failure. This has been advised by Click and Clack and Ford mechanics.
One indicator of impending doom, so to speak, is the lighting of the Check Engine light. If you have a ScanGauge installed or have some other method of reading the output of your OBDII socket, you'll probably see a Diagnostic Trouble Code of P0190, Fuel Rail Sensor. If you don't have a way to read the OBDII output, your mechanic will be able to. At first the Check Engine light will come on sporadically, but will increase in frequency over time. The risk is that sometime, somewhere, where you least expect it, the pump will fail for good, leaving you stranded.....hopefully not out in the boonies.
In addition to all the above, there seems to evidence that there is a defect in the new fuel pumps and that Ford is aware of it. A Ford dealer has told one owner that this is the case, but Ford apparently has not notified any users.
Replacing the fuel pump is expensive - the gas tank must be dropped to obtain access to the pump. That in itself is a major part of the roughly $1500 cost of the pump replacement.
You may be able to reduce the cost considerably by getting the fuel pump yourself and having the installation done at an independent garage. This is what Alex Rutchka did when his pump died while in Alaska. He ordered the pump, Airtex E2437S (for 2005 Ford E-450 Econoline 6.8L 415 cid V10 FI) from www.RockAuto.com. The pump plus shipping to Alaska was $270 and the installation labor charge was $400.
If you have the right tools and equipment, you can tackle the job yourself (assuming you're at home and not on the road). You can get the fuel pump (DELPHI FE0298) and fuel strainer FSO127 from NAPA or a Ford dealer. Air tools will help, as will a big floor jack with which to lower the tank. One RV'er who took on this job says he got it done in a weekend. The fuel pump itself was quite easy to replace, getting to it was not much fun. The hose clamps were rusted on the fuel filler lines and had to be replaced.
The pump used on fuel injected trucks had a design flaw. In '97, they changed the design. You need to use a '97 pump if you want a permanent cure. The electrical connections on the newer
pump won't fit your truck, so they sell an adapter kit for it.
Contributors: Steve Kocan, Ron, Alex Rutchka, Darrick, Nels, Victor Sanchez, WxToad
Revised:12 Oct 13
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