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Help 1989 Mack 350 dies under a load



Loses its prime when sitting then hard to start . The truck will start and idle and rev up fine but put it on the road and it dies. It also doesn't want to build rpms unless going downhill. It will restart after it dies and idle and run under no load. Changed fuel filters twice. The fuel is probably two years old but looks and smells ok. Where do I go from here? Thanks Gents.


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Hi Butchee,

I was about to say fuel blockage, but you replaced the filters. Other blockages e.g., blocked or kinked fuel lines, air filter. Is the pump delivering sufficient fuel?

You said "loses its prime". Do you mean you have to pump up the fuel or even bleed the air out? If yes, there is a leak. You may not see fuel leaking as the fuel is not under pressure, but it sucks in air - just enough to give you grief, but not enough to totally stop you.

I guess this is too obvious and you already knew it.

Hope this helps, Tony

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It sounds like maybe sucking a small amout of air on inlet side try looking at that have come across that a few times in my career.


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