I have a 93 GMC 3500HD with the mechanical 6.5. If the truck sits for any time at all, you have to crank and crank on it to get it to fire off. If you shut it off and immediatly restart, it fires right off. Its acting like the fuel is draining back to tank, There are no external leaks present. The electric transfer pump on the frame is being powered up and is pumping, Can anyone help me? Thanks DJ

 

It might be a glow plug problem.

 

glow plugs are good, it was in the 80's today, and it isn't dependant on engine temp.

 

One thing that you might check is the return line fitting on the IP. It has a glass check ball in it and if it plugs up it will cause problems. Also putting a piece of clear hose on the return would let you see if air is getting into the system. The seals in the IP could be going bad but usually that would let fuel leak into the intake valley.

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Have you tested the fuel pressure from the lift pump?

 

i'd say the check valve too i used to have a 6.5 in my truck and had a similar problem i cleaned the check valve it was plugged up with sludge and that seemed to correct the problem

 

updates??

 

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