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1998 ch612 fuel problem


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I have a 1998 ch612 with a v-mac II E7 350 in it. It has a Bosch injection pump on it. After sitting as little as five minutes, it is as though the injection pump has lost it's fuel. It will start and run but only for about 8 seconds then it stumbles and shuts down from fuel starvation. I've read lots of posts here concerning fuel prime loss and have checked/repaired/replaced as much as I can with no positive results. Fuel crossover in head checked... no leak. Hose from head to return tee on pump replaced... btw, neither fitting for hose is check valve... suction and return lines from pump to tanks checked... vacuum tested... no leaks... fuel filter replaced... orifice type fitting on pump for return line replaced (Mack dealer's suggestion)... transfer pump/hand primer pump replaced (Mack dealer's suggestion)... lines from transfer pump to pump checked... no leaks.

If you pump the hand primer after the engine dies, it does build some slight resistance at first then loses its resistance for about 12 to 20 pumps, then develops slight resistance again but unlike cat engines with hand primers, it never gets solid... it keeps flowing fuel back to tank and engine is still difficult to start. If I pinch off main return hose and pump hand primer it gets solid and engine fires immediately. I've seen references to check valves, overflow valves, etc. but according to the Mack dealer and the local big truck fuel injection shop, this model was not equipped with either. Unfortunately, now my thoughts turn to some internal problem in the injection pump.

Any other hints, tips or suggestions for things to check before sending the pump out for repair would be greatly appreciated.

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