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Matt, Engineer
Category: Car
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Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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Isuzu truck NPR hd diesel: I have a 2007 Isuzu diesel NPR hd

Resolved Question:

I have a 2007 Isuzu diesel NPR hd truck, 70,000 miles. Very hard to start, must manually push priming button on top of fuel filter assembly to start. Once started will idle and run moderate power acts like air or bad fuel. No air in system, fuel inj cleaner added and replaced filter twice. Is there a possibility if bad wiring of bottom of fuel separator in filter?
Submitted: 1 year ago.
Category: Car
Expert:  Matt replied 1 year ago.
Hello

sounds like it may have developed an air leak on the fuel supply pipe from the tank to the engine. The engine has no separate lift pump and relies on the built in one in the injection pump. If a leak has developed on the fuel suction pipe then air entering the system will air lock the pump.

Try pumping up the fuel using the hand pump in the engine bay on the filter housing, then crack off / loosen each injector pipe in turn while cranking the engine and getting an assistant to operate the primer. This will expel air from the injection side and the engine should fire up. The problem will be cured by checking the supply pipe along its length for signs of leakage and repairing any you find.

If you daub each pipe joint with heavy grease and the issue goes away then wipe the grease away one at a time to highlight the problem joint

Matt, Engineer
Category: Car
Satisfied Customers: 16722
Experience: Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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