Medium and Heavy Trucks
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Yes runs a little rough then clears out
Most often the regulator and the fuel pump are the cause of fuel leaking down. But if you have changed the regulator and fuel pump, and there are no codes. I must next suspect the engine speed timing sensors. I have seen them cause a hard start before.
The engine has 2. One is the primary start sensor and the other is the primary run sensor. When the lower primary start sensor is faulty, It can cause hard. To confirm, I like to check AC voltage to the injectors while cranking. You should have 20-40 AC. If you do not, I would suspect the engine speed timing sensors. IF you do have 20-40 AC, Then I would suspect a fuel supply problem. The engine needs at least 25 psi to start. I would put a psi gauge on the system to check the fuel pressure.
Please reply back if you need more help or have more quesitons. I am happy to assist.