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Diagnosing diesel no-start problems

Low oil can cause a no start? It just might.
Thursday, January 23, 2014 - 09:00
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The only code stored in memory is the P2623. The code description is open circuit for the IPR (Injection Pressure Regulator) circuit. 

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Stop and think about engine compression. In a combustion chamber, there are only four places for the compression to escape: through a leak in the combustion chamber (cracked head or leaking head gasket), through a leaking intake valve, through a leaking exhaust valve or through a leak in a piston or piston rings. I find it easier to find where the compression went and in these cases, it is easy to check for pressure pulses in the intake manifold, the exhaust pipe, the engine crank case or in the engine cooling system.

This process will require a labscope and a FirstLook sensor. but in most cases the process will be quicker and more reliable than having to remove parts and engine components in an attempt to gain access to a place to get an actual compression reading.

The Need for Proper Fuel Injection
After the proper compression has been verified, the technician needs to verify proper fuel injection. Here is where things start getting a little complicated. Back in the day of the mechanical fuel injection systems, it was easy to loosen a high pressure fuel injection line and see if fuel was being delivered to the fuel injectors. In the world of today, this is a little harder, if not downright impossible.

The 6.0 Ford engine is shown with all the accessories covering the engine.

With the advent of the electronic diesel fuel injection system, a scan tool and scan data will be your friend. If you are working on a HEUI (Hydraulically actuated, Electronically controlled, Unit Injector) system like those found on Ford, Navistar and some CAT engines, you have PIDS (parameter identification) for several different things. Because Motor Age focuses on the light duty market, we’ll focus on Ford, specifically the Injector Control Pressure (ICP), Injector Pressure Regulator (IPR) and fuel injector pulse width PIDs.

A tip on using scan data of HEUI Ford Powerstroke engines: When watching the ICP, don’t rely on the pressure ICP pressure PID, instead use the ICP volts. The reason is simple. On a long crank/no start, the Powertrain Control Module (PCM) can use a substitute number for pressure. The pressure voltage, though, is always correct. If you are working on a common rail diesel fuel system, the injector rail pressure PID is the telltale PID on fuel pressure. All common rail engines have a pressure sensor in the high pressure rail. If this sensor is showing the proper amount of pressure, you can be assured there is pressure in the rail. But you have to ask, “Is this pressure air, combustible fuel or some other liquid?” Any time you are dealing with a cranks/no start, it is very important that you verify fuel quality. There is nothing worse than working for an hour or so before finding out the fuel tank is full of gasoline or some other liquid that will not combust in the combustion chamber.

With the degas bottle, the air filter and the FICM removed, the IPR is visible but not readily accessible. 

Once the proper compression and fuel pressure have been verified with a scan tool and the engine still will not start, the next step is to determine if the fuel is being injected into the combustion chamber. Over the years, I have seen many no start problems caused by stuck fuel injectors. This year alone, I have had three vehicles that needed a set of new injectors to resolve a no start problem.

A good way to verify fuel injection is to watch the tail pipe while the engine is being cranked. If fuel is being injected into the combustion chamber, some fuel will be blown out the tail pipe. Now, on vehicles with a catalytic converter and a Diesel Particulate Filter (DPF) this might not work, because the fuel vapor can get lost in all the exhaust components. As a last resort, it might be a good thing to pull out a glow plug (if the engine has glow plugs) and give the engine a crank. If fuel is being injected into the combustion chamber, there will be a nice cloud of atomized fuel being blown out into the air.

I am a little reluctant to grab a can of starting fluid and start spraying it into the air intake. Over the years, I have seen a few engines badly damaged from this quick start method. If the engine has the proper compression, the proper cranking speed and the proper amount of fuel injected at the proper time, the engine will start.

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