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Diagnosing diesel no-start problems

Low oil can cause a no start? It just might.
Thursday, January 23, 2014 - 08:00
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This IPR has been removed from and engine. Notice the heat shields fastened around the solenoid. Any time you are working on one of these engines, make sure the heat shields get replaced and securely fastened. This solenoid lives in a very hot climate, nestled down under the turbocharger and alongside an exhaust pipe

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Start With the Fuel System Basics
Before a technician can start on any diagnostic problem, he or she needs to be aware of how the system works. Back in the day, this was simple since there were only three different kinds of fuel systems. Cummins used the PT system, Detroit Diesel used their unit injector and everybody else used a version of the Pump Line Nozzle (PLN). Today we have common rail, hydraulic unit electrical injector (HEUI), some PLN systems and a few different versions of unit injection. Before you start on a diagnostic problem, I would encourage you to get familiar with the fuel system and your scan tool. The bidirectional tests and controls from the scan tool will be where you do most of your testing and problem analysis.

On to the Application
The problem vehicle in the bay is a 2005 Ford F550. Checking the VIN found it was powered by a 6.0L diesel engine with an automatic transmission. The odometer shows it has traveled 98,000 miles. The owner said the engine had died when rounding a left-hand corner, but the engine restarted and had been driven back to their business. The next time the truck was needed, the engine would not start.

Cranking the engine found the FICM sync and sync were both yes. Cranking RPM at 138 is a little slow, but the truck has been sitting outside in 15 degree weather. The IPR is commanded at 85 percent but the ICP voltage only made .67 volt. This oil pressure is too low to get the engine to start. This data is showing me there is a high pressure oil leak and combined with the P2623 I can be assured the problem is an open IPR regulator. 

Because any diagnostic problem starts out with information gathering (clues to the mystery), I want to know if there are any Diagnostic Trouble Codes (DTCs) stored in memory. In this case, there is only one DTC stored in memory; a DTC P2623 is set for a circuit problem in the Injector Pressure Regulator (IPR) circuit. Some things that come to mind that could set this code would be such a simple thing as the IPR not being plugged in, but it also could be an open circuit in the IPR coil. By retrieving this code first saves a lot of diagnostic time, since I can rule out a lot of other things that can cause a no start.

If this engine were a 7.3, it would be easy to just do a visual of the IPR and see if the plug was in its socket but in this case, the IPR is buried down under the turbocharger, covered by the coolant degas bottle and the Fuel Injector Control Module (FICM).

Everything is there for this engine to run; proper cranking speed, proper ICP, the only thing lacking is combustion. In this case, I did not warm the glow plugs, thus the lack of heat in the combustion chamber and the engine no start. 

Before you start removing parts and poking around for a problem, it is always a good idea to spend a few minutes with the scan tool and gather some data. The stored code is a circuit code, but how much time could be wasted if the problem were something else besides the circuit problem? One reason I suggest some scan tool testing is because there are a lot of parts that need to be removed to gain access to the troublesome part, and most of these parts must be installed before the engine can be started.

One clue that is sticking in my mind is the engine stall when rounding a left-hand corner. Because this engine is dependent on proper oil pressure to make the fuel injectors work, it is a must that the technician start by checking the engine oil level. In this case, the oil was at the top mark of the dipstick. The next step is to hook up a scan tool and select some important PIDs applicable to the injection system. Selecting the three FICM voltages, Engine RPM, the ICP voltage and IPR percentage will give a good indication of the hydraulic control of the fuel injectors. By using these data PIDs, the technician can also get a good indication if fuel is being injected into the combustion chamber or if the combustion chambers are hot enough to start the engine.

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