94-97 OBS Ford Powerstroke owners have actually the included potential complication of a fuel tank selector valve in the suction next of your fuel system. This valve switches the supply and return connections between the 2 different fuel tanks in the truck. Nevertheless of whether the van is still running the OEM mechanical fuel pump in the valley, or has actually been updated to a more contemporary electric fuel pump system, this valve can cause some drivability or power issues. The selector valve itself isn"t rebuildable or repairable, so this post is really more of a quick explanation of just how the valve works and how to identify if the valve is bring about you a problem.
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I DON"T care HOW it WORKS, simply TELL ME IF IT"S BROKENFor those merely trying to diagnose a problem, there are some things to consider. First, if the worry exists v the selector move in just one position, one of two people Front or Rear, the problem is going to it is in somewhere in between that details tank and the selector valve. Normally speaking, if you fill the affected tank and also the trouble goes away until the level drops to a particular point, the difficulty is IN the fuel tank (broken pickup screen, cracked pickup tube, etc). If it makes no distinction what the fuel level in the tank is, the problem is likely in between the height of the tank and the selector valve. If you have actually inspected the supply heat from the tank come the selector valve and it is not damaged, kinked or obstructed in any kind of way, over there is a great possibility that the valve itself is the problem. In the situation of a problem that only exists through one tank, and also where no concern can be uncovered with the tank or the fuel lines, every the above, you usually won"t go wrong by just replacing the selector valve.If you desire to be certain that you don"t have troubles from the selector valve back to the tank(s), the easiest technique is to usage a "Bucket Test". Check out this write-up for details on performing "Bucket Tests". The goal is to bypass the fuel tank(s) and also tank come selector valve it is provided lines to watch if the trouble goes away. One at a time, disconnect the larger SUPPLY line from the inlet that the selector valve (either former or rear port) and also connect a short-lived hose from the selector valve to an alternate container that fuel. If the device operates generally when running from a "Bucket", but not as soon as running from the fuel tank, the trouble is in the tank or it is provided lines.If the device still does not operate normally, girlfriend will desire to bypass the selector valve next. In this case, discover a place in the supply heat after the selector valve to disconnect and reroute come an alternating container that fuel. With the pump illustration from the alternating container, if the device operates normally, the selector valve is the problem and also needs to it is in replaced.WHY does THIS thing FAIL?The fuel tank selector valve have the right to fail in a number of ways. The system uses an electric motor v a threaded shaft to move the valve plungers from one position to the other. Once the switch is flipped to readjust tanks, the electric motor is engaged, moving both plungers (supply and return) and also a pair the internal electrical contacts (one because that the electric motor, one because that the fuel tank sending out unit signal). Once the electrical call moves much enough, it division the electrical connection, preventing the motor. Once the move is flipped to the other tank, the polarity is reversed and also the electrical motor turns the various other direction, relocating the plungers and also contact back the various other way. Again, once the electrical call reaches the end, the electrical motor stops. Due to the fact that the system moves follow me a threaded shaft, over there is no default position, the plungers deserve to be stopped anywhere in their selection of travel. Anything that stops the electric motor from transforming the threaded shaft stops the valve from an altering position (failed electric motor, electrical connection problem, etc).
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If the threaded obelisk breaks or strips, the valve doesn"t move. Because the motor is little and weak, if something stop the plungers from relocating (debris in the valve), it deserve to prevent the valve from totally switching to one or both tanks.In a nutshell, the plungers can end up grounding in any position along their selection of travel, and also that selection is long enough to allow for partial circulation from one tank through no flow from the other, or also no circulation from either tank.
Author: Dennis Schroeder - Co-Owner of strictly DieselDennis has actually been Designing, Building and Supporting Aftermarket Fuel systems for 7.3L and 6.0L Powerstrokes since 2001.