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Diesel Fuel Shut off Valve Functions-Issues

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This fuel shutoff valve is a part of the injection pump that functions as the shutoff of fuel and engine.  It is operated by a current from the battery through the ignition switch.

When the ignition switch is on and current goes to this shutter it opens and fuel will flow to the injection pump that supplies the nozzles spraying fuel to the combustion chambers. When the ignition switch is off this valve will close and no fuel will flow to the injection pump.

How Diesel Fuel Shut off Valve Functions-Issues-shut off valveHow Diesel Fuel Shut off Valve Functions-Issues-shut off valve

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I would like to share with you our experience in the Toyota L engine. We have just overhauled it, the radiator was overhauled too, and the injection pump calibrated.  Everything should have been fine as expected.  The engine was cranked and it started smoothly, the engine noise is just right, the thick white smoke is gone and is about to be on a road test.

But as the engine is warmed up it suddenly stalled, no matter how you crank it in order to start it didn’t. Because it’s newly overhauled maybe the fuel has not yet fully saturated the injection pump and air maybe inside. The remedy is to loosen the nozzles so that air may be blown out.

This process if the air had been totally out from the injection pump fuel should follow to come out of the nozzles. If there are no bubbles coming out it’s time to tighten it.  Loosening the nozzles to test if there is fuel in it should be done one after the other.

However, this time there was no air coming out and there was no fuel too.  So how would the engine start if there is no fuel supplied by the nozzles? It will not. It’s good the fuel hose is transparent and obviously, the fuel is still sufficiently available from the tank.

The next step is to check if there is a current going to the fuel shutoff valve.  So we checked it and there was no current.  Upon examination, it was the wiring connected to the shutoff valve that has been cut off inside, however, it was not obvious until we stretched it out and it was only connected temporarily through the insulation of the wiring.

When the connection was restored the engine was cranked and it started until it was tested on the road and until this time of writing the engine did not stall.

6 Comments

  1. Great explanation of this problem.  I love working on cars and often search for issues that elude me.  Wiring is a nightmare and finding an open or shorted wire can leave you pulling your hair out.  I like how you explain the function of this component so it is easier to understand the possible issues related to the problem.

    • You are right Jeffrey, wiring issues are so difficult to solve especially when the car is an old one because some of them might have been melted somewhere, others may have been consumed by rusts and other causes. Sometimes we discover them accidentally.

  2. Hello Accad, very good and informative article about (diesel) fuel shutoff valve functions. This valve has actually very important function, if it `freezes` car will stop. Your example from Toyota car can be very helpful! And by the way, Toyota cars are very good and I`m not surprised that the problem which you described was just because of wiring connection. Thanks for sharing with us!

    • Hi, Luke, thank you for leaving a comment on this post. I was surprised then that this part can freeze in cold areas and yes if it happens fuel will not flow in it.

      The wiring connection issue may be because of longtime use of the car and may have unconsciously stretched during repairs of other parts.

      It’s good tests can determine and identify where the issue is and it’s addressed properly.

  3. Thank you for this informative review of the diesel fuel shut off valve functions. So good that you shared your Toyota experience on here. I think proper check should always be done if the noozles is supplying adequate fuel to the engine.and the wiring should also be double checked because if it is tampered with there won’t be flow of current and it will lead to engine getting stalled at intervals. 

    • You are right Clement if the engine doesn’t crank while the battery is working good the first thing to be checked is the fuel and the question, is there a fuel flowing from the nozzles? So we have to check them one by one and that is what we have done. 

      It was surprising that all the four nozzles were dry so we have to check the injection pump parts that supply the nozzles. The first thing to have in mind is that what controls the fuel supply to the injection pump? And that is was the fuel check-valve.  When it is closed no fuel will go to the injection pump and the injection pump cannot bring any amount of fuel to the nozzles for ignition.

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