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Force a Diesel Engine to Stop

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Engine diesel Force stop

Force a Diesel Engine to Stop

Diesel Troubleshooting Article

© Copyright 2000 - 2007 Chuck Kopelson 12/12/2004
Updated September 21, 2009

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Why in the world would you need to know how to shut down a diesel? An owner recently had his ignition switch go bad. The key wouldn't turn back to the off position. He couldn't shut off the engine. A pure mechanical diesel engine unlike a gas engine does not need an electrical spark for ignition. On a gas engine all you have to do is take away the electricity and the engine can't run. A diesel uses the heat of compression to ignite the fuel so removing the electricity from a diesel may not stop it from running.

There are of course, exceptions to this. All modern diesel engines use some electrical devices to operate. Almost all diesels have an electrically operated fuel shutoff solenoid and electric fuel lift pumps. Others like the turbo diesels use an electronic injection pump. As long as these engines are getting air, fuel and electricity they will continue to run. Cutting off the electricity to these engines should stop them. One exception would be a N/A diesel with a malfunctioning fuel shutoff valve.

There are circumstances where a malfunctioning engine runs away. An internally leaking turbo occurs when you place a board over the air intake and cut off the air supply. This creates a strong vacuum in the intake system which causes engine lubricating oil to get sucked pass the seals in the turbo; the engine will then be running on the motor oil. The engine won't stop until all the oil is sucked out of the engine and the engine seizes.

In many vehicles, a crankcase breather pipe feeds into the air intake to vent the crankcase. On a highly worn engine, gases can blow past the sides of the pistons and into the crankcase, then carry oil mist from the crankcase into the air intake via the breather.The engine will run on this oil mist, since engine oil has the same energy content as diesel fuel. The engine revolutions increase as this extra "fuel" is taken in. As a result of increased revolutions more oil mist is forced out of the crankcase and into the engine, and a vicious cycle is created. The engine reaches a point where it is generating enough oil mist from its own crankcase oil that shutting off the fuel supply or cutting the ignition will not stop it and it will run faster and faster until it is destroyed.

Never disconnect the battery from a running truck. You may ruin the alternator. Disconnecting the battery won't stop the flow of power because the alternator is still spinning generating power.

All the Hummer diesels have electric lift pumps that suck the fuel out of the tank through a filter and deliver it at low pressure to the high pressure injection pump. These lift pumps have had problems where they just stop pumping. As long as the fuel line doesn't have any leaks the engine will continue to run because the high pressure injection pump has enough pulling power to suck fuel from the tank on it's own. That's why disconnecting or disabling the fuel lift pump will not shut down the engine.

You are probably asking yourself, why all the bother with cutting off the fuel pump when you lose oil pressure if that won't stop the engine? The cutoff isn't to protect the engine, it's to protect you from fire if you are in an accident. It guarantees that the fuel pump will stop pumping fuel where it could be dumped all over the engine compartment after an accident.

The hmmwv's and the Hummer N/A (naturally aspirated) diesels have mechanical injection pumps. All the turbo diesels have electronic injection pumps with computer controlled engines. Both pumps have electrical fuel cutoff solenoids. This is how the engine is shutdown when you turn the key off. If the ignition key doesn't work and the solenoids are working you should be able to shut down a diesel by closing the solenoid and shutting off the fuel supply to the engine. You have to find the electrical connector to the solenoid and either pull it off or cut the wires.

On the electronically controlled trucks (99 and newer) you can fool the computer into shutting down the engine by pulling the oil pressure sender on the top of the engine. The computer will think you lost oil pressure and activate the fuel cutoff. On a Pre-'99 TD truck pull fuse 6B - PCM / Ign Power / Brake Switch. On a '99 to '03 truck pull the equivalent fuse. This will cut the power to the electronically controlled injection pump and cause the engine to stop. You can also pull the plug going to the FSD/ PMD if you can reach it. If you have a remote mounted setup this would be very easy.

If the fuel shutoff solenoid is broken go to the fuel filter housing and open the air bleeder (black cap on the top) or unscrew the top of the filter housing. This will let air bleed into the fuel system and stop the engine. If you do stop the engine in this manner you will have to purge the air to get it started again.

The engine can be shut down by restricting the fuel return at the injection pump.

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