In truth, the information on the most common starting problem with a Duramax engine applies to nearly every diesel engine, large or small, on the market today. Most diesels work about the same in terms of both electronic controls and core function, as it applies here, so this will likely be the probable cause for a non-start on a 4-cylinder car diesel on up to a huge 8-cylinder heavy machine.
The symptoms are simple and were outlined by dlt630 in our Ask a Mechanic forum recently:
Duramax Diesel 6.6 . Will not start. Not even on starting fluid. Won't even try to fire up. Any thoughts ? Timing chain maybe ? Thanks.
Know Your Engine
Before we get started, let's clear up some things about dlt's question here. First, the Duramax (and many diesels) doesn't have a timing chain. It uses gearing on the front of the engine to create its timing.
Many diesel engines are "straight" rather than "V" shaped, so they have one camshaft and head rather than two. Therefore, a chain would be unnecessary complexity that a couple of simple gears can replace to give the engine more reliability and less maintenance problems. The probability of these gears going out of whack is less than remote.
Next, the basic operation of a diesel engine is such that starting fluid will be hit-and-miss. Because of the way diesels work, through compression rather than spark, starting fluids commonly used to get the engine to "fire" will not always work. This is one likely reason that dlt's attempts aren't working, but there is another explanation as well.
Finally, most diesels will have trouble starting up if they have any kind of fuel blockage at all - water in the fuel, clogged filters, gelling due to low temperatures, etc. So always rule out fuel delivery problems before checking anything else. The easy way to check is to see that the fuel pressure after all filters is on spec.
The Fuel Pressure Relief Valve and Sensor
The most common problem with a non-start that has plenty of fuel pressure to the injectors is the fuel pressure relief valve (FPRV) and/or its sensor.
Nearly all modern diesel engines have one. It's a valve on the high pressure fuel rail that shuts off all fuel to the system when the ignition is shut down. It's literally how most diesel engines turn themselves off, since you can't just kill the spark (as with gasoline) to shut off a diesel.
The FPRV closes off all fuel to the engine and is the reason that today's diesel's no longer "tractor" to a stop as they did not too long ago. When the ignition is shut off, it triggers the FPRV to close.
The sensor on the FPRV checks for fuel flow after the valve is closed, tells the engine whether the valve is closed (or not), and more often than not acts as a safety device to keep the glow plugs shut off should the valve be malfunctioning.
So, when you turn off the ignition on a modern diesel engine, the FPRV closes and its sensor kills power to the glow plugs. This eliminates all possibility of the engine running.
On many engines, if the FPRV sensor is "triggered" then several other things also change in the engine's computer controls, including slowing the cranking so that compression to ignite cannot be achieved.
If there is something wrong with the FPRV or its sensor, then the engine will give off a code. Most likely it will be related to the fuel flow, giving a low pressure warning or similar.
Testing the FPRV is simply a matter of attaching a fuel pressure gauge to the fuel line after the sensor and cranking the engine to see if pressure reaches optimal. Testing the sensor is not as easy without special tools or a replacement sensor to try.