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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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With the glow plugs warmed, the engine started. This data shows the same data PIDS as the preceding data capture, the only difference is the combustion chambers had the proper heat to get the engine to start. 

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The scan data is showing the ICP voltage will only make it to 0.67 volt. Keep in mind that this vehicle has been outside in 15 degree Fahrenheit weather all night. The oil is quite thick, so the cranking rpm is a little slow at only 138 rpm, but the key to this problem is the low ICP voltage. The HEUI injection system needs a minimum pressure of 0.8 volt of ICP before the fuel injectors will be pulsed. In this case, this ICP voltage is also a great indicator the IPR is stuck open. The IPR is a pulse width modulated pressure regulator that normally is open. Without an electrical connection, this pressure regulator will never close to build the proper oil pressure to operate the injectors. The next step in this diagnostic process is to remove some parts to verify an electrical problem.

With the degas bottle, air filter and FICM removed, the IPR can be seen and touched, but the plug and wire are buried under the solenoid and the heat shield that protects these electrical parts from the heat of the exhaust pipes and the turbocharger. A look down in the hole with a bore scope found the suspected plug not properly seated in its socket.

With the IPR control wire plug properly installed, the FICM was plugged in. The first time the starter turned the engine, the engine fired right up and ran smooth.

With the engine warmed to operating temperature, the engine at idle, the IPR command at 23 percent is a good indication there are no high pressure leaks in the injection system

After any repair, the vehicle needs to be driven until it reaches its operating temperature and the engine data checked again with the scan tool. In this case, since this no start problem was caused by lack of ICP, I am interested in the high pressure oil that operates the fuel injectors. Selecting the RPM, ICP, IPR percentage and Engine Coolant Temperature (ECT) will give the information needed to verify the high-pressure oil problem is fixed.

The best time to use the scan data to snoop out a high pressure oil leak is when the engine oil is hot and the engine is idling. In this case the IPR percentage is showing 23 percent at hot idle. When the engine was shut off and restarted, it exhibited a quick start and the IPR percentage is still at 23 percent, so I can rest assured there are no high pressure leaks in this system. This truck is ready to ship and put back to work. 

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