Why Won’t My Diesel Start?

What It Takes To Make a Diesel Run

There are only three things that are needed to make a diesel run;.

(1) Heat from compression,

(2) Fuel at the Right time and pressure.

(3) Sufficient crank shaft speed to provide the compression. The engine must also have sufficient air.

A diesel in the purist form is a very simple engine.

What makes a diesel hard to start?

  • If the fuel is not injected into the cylinder at the correct time the engine will be very difficult to start. The fuel needs to be injected before the piston reaches top dead center to create a flame front in the cylinder. The timing is critical for correct engine operation.
  • If the fuel injection pressure is not sufficient the engine will be hard to start. Injection pressure is difficult to test and usually manifest it self in hard starting, lack of power and sometimes smoke from unburned fuel.
  • The engine must crank at sufficient speed to provide the necessary compression, heat in the cylinder to ignite the fuel. Many hard starting problems with diesel engines can be attributed to a poorly functioning starter.

How can I the do it yourselfer check some of these things?

If you own a diesel and are going to work on it, it might be worth while to invest in the tools to set the fuel injection timing. There are many methods of setting the timing of a diesel. Some older diesels use a drip tube. The V.W. diesels us a dial indicator for checking pump plunger travel on the IDI engines (Indirect Injection). Some of the Cummings diesels are timed in the same manner. Some of the new diesels are timed using a scan tool to inter face with the engine management computer.

If you are going to work on your diesel, buy a book, preferably the factory manual.

You can check to see if all fuel filters are clean.

You can check to see if your glow plugs are working. The best method that I have found to check glow plugs is to use a direct current (DC) amp clamp. This is a meter that clamps over a wire and read the amount of current flowing through it. Most glow plugs pull about 9 amps after the initial surge. You can get the correct figure from the manufactures technical data. DC amp clamps are a lot cheaper now than they were in the past. I bought the small hand held unit that our shop uses for Sears for under $50.00. If you use starting fluid in a diesel with glow plugs it nearly always burns out the glow plugs even if they are new ones.

The amp clamp that you bought to check your glow plugs is a good tool to check your starter. Measure the current draw of the starter and compare it to the manufacturers specifications. Any thing beyond these simple things will require specialized tools and knowledge.

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