The most common mechanical problem with the 12 Valve Cummins Injectors was failure of the Bosch Vp44 injection pump and lift pump. Over the years these have been notorious for going out and costing consumers a lot of money, especially if you take your truck back to the dealer, repair cost usually average about $3000. There are three common mechanical failures of the VP44 injection pump:
The most common mechanical failure of the VP44 pump is rupturing of the diaphragm in the front of the injection pump. The diaphragm ruptures allowing the timing piston to vibrate and damage the front cover until fuel bypasses. This will cause the dreaded check engine trouble code P0216. When this occurs your Nozzle Head Rotor Spraying System must be replaced. The rupturing of the diaphragm is caused by a poorly designed lift pump. When the lift pump does not supply the Injection pump with the correct amount of Fuel Pressure (a minimum of 5 psi under load at wide open throttle) the diaphragm then doesn't have enough positive pressure and ruptures. Dodge has recognized this problem as they will no longer even sell the lift pump that goes on the side of the block. They replace it with a unit that is now mounted in the tank. The average cost of having the lift pump put in the tank is about $800.
The next most common mechanical failure of the VP44 is that the Pump Fuel Bosch Head Rotor seizes in the head of the pump. This again can be contributed to the lift pump not providing enough fuel to the injection pump. Diesel Fuel is used as a lubricant, so when there is an insufficient amount of fuel the rotor does not get lubricated properly. If the rotor seizes the truck wont start and the VP44 Injection Pump must be replaced.
While, the last reason for the failure of the VP44 pump is electrical problems with the computer on top of the pump. Heat is the main reason associated with this problem, causing the soldered components to become crystallized over time and make bad connections. Lack of fuel is again part of the problem, because the VP44 is cooled with fuel instead of oil (as the old P7100 12 valve pumps). When this problem occurs you will usually experience intermittent hard starts, white smoke and what's usually referred to as "The Dead Pedal". More details at cnboqiang
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