6.9 Diesel Won't Start

The most basic causes for a diesel engine to not start include lack of fuel, air in the fuel, contaminants in the fuel, a defective injection pump, incorrect oil grade, low compression, low battery and faulty glow plugs. Your goal is to work out which of these is causing your starting problems.

Start with the obvious and check your tank to be sure you have fuel. Review the manual and be sure you are using the right starting procedure given the weather conditions. Are you cycling the glow plugs enough? If the temperature is colder than 20 degrees Fahrenheit you may have to bring the vehicle into a warm shop before it will start. Refineries alter their diesel mixtures to adjust for summer and winter conditions and if you are using summer diesel in cold conditions you might be getting clouding in the fuel.

Are the glow plugs working properly? You can remove them and check with an ammeter that they are getting power. Remove a glow plug and crank the engine to see if fuel vapors come out of the glow plug hole. A lack of vapors indicates the fuel is not getting through to the injector pump. If vapors are coming out of all of the glow plugs you likely have contaminated fuel and need to flush the fuel system.

If fuel is not making it to the injectors, check if the fuel return line is blocked. Check for black particles in this line in case the governor weight retainer ring has partially disintegrated. If the return line is not blocked, check that fuel is making it to the injector pump. Do this by removing the fuel line from the fuel filter on the injector side of the filter. Fuel should spray from this line. If it doesn't, the filter is blocked and needs replacing.

Check to see if fuel is getting to the fuel filter by removing the inlet hose and cranking the engine. Fuel should come out of this line. If it doesn't, the problem could be further down the line at the fuel pump. Lower the fuel tank and clean the fuel filter. Check the fuel pump to see if it is operating properly.

In some cases the fuel solenoid is either faulty or not getting power. Pull the pink wire from the top of the injection pump and turn the ignition key to the on position. Briefly make contact between the pink lead and the injection pump. The pump should make a clicking noise. If it doesn't it is likely faulty and will require replacement or maintenance.

If your 6.9 L diesel has been running rough before not starting, you should check the injector timing. You can do this by checking that the timing marks are aligned or use a timing meter.

Diesels don't use a spark plug to ignite the fuel, but they do require a good deal of electrical power to operate the glow plugs and injection pump. If your battery or alternator are beginning to fail, you might have enough power to crank the engine over but not enough for ignition, or the engine will run and quit. Have your battery and alternator tested.

Another factor that may be preventing fuel getting to the injectors is air in the fuel lines. This occurs when connections are not tight or fuel hoses have cracks or other defects. The cure for this is to locate the source of air, repair it, then bleed air from the fuel system. If your engine is getting old or hasn't been maintained well, check the compression, injection pump and injector nozzles, as these will eventually malfunction or fail.