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Where are you bleeding air from the fuel system. Is it at the schrader valve at the front of the fuel manifold?
Yes. And the filter housing maintains full pressure.
We've have been having this problem for three weeks and just can't get our hand on the problem. We're are tired of throwing parts at this truck.
The truck use to be able to go out on the route and last for 6 hours. The truck went out yesterday and only lasted 2 hours.
If you have no air in the fuel at the filter housing , but seem to be finding a lot of air in the fuel manifold , then your problem is likely going to be compression leaking by the injector bore and getting into the fuel manifold .
compression then slowly builds up in the fuel rail to the point that you start developing what seems like a miss and then gets to the point that the engine dies . Then , you are force to hand prime and bleed air out of schrader valve on front of fuel manifold.
If you are certain that there is no aerated fuel coming from the tanks and the filter housing , then the compression gasket on the ends of the injectors are leaking and compression may be coming into the fuel system. I just answered a question similar to this problem and it ended up being his injectors ( they were loose) . I would pull them all out , replace all o-rings and end gaskets , clean the injector bores and make sure there are no end gaskets stuck in the bottom of the bores. Then, if the injectors are fine and the tips are good, re-install them and torque to 30 ft/lbs. Reseal the high pressure oil rail again with new seal kit (have to replace rail seal kit every time you pull it off ) and re-install . Torque it to 23 ft/lbs starting with the center bolts and working your way out towards the end bolts.
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If in doubt , I would definitely have another look at it with a magnifying glass to be sure there are no hairline fractures anywhere on the tips of each injector and also further above towards the lower o-ring . Fractures are all too often overlooked and easily missed.
And remember, everytime you remove the high pressure oil rail to get to injectors, you MUST replace the oil rail seals again to prevent leakage . Those seals have to be able to hold up to 4000 psi of hydraulic pressure for proper actuation of injectors .