Little Boost then no Boost
 

2000 F350 Superduty 7.3L 2wd manual trans

The truck runs fine on flat ground. When I walk on it I am only getting 5 - 6 pounds boost which it holds for a few seconds then drops off to zero and run very rough until I pull over, shut it off for a few seconds and then it will smooth out. Down shifting and easing off the gas does not make it run smoother. It will also start to run if I crest the hill and start down. Same thing when climbing long hills, even without a load. No codes and no fault lights. I tried disconnecting the map and I get service engine light but no change in performance. Does not blow any smoke. I did change out the HPOP O rings a few weeks ago but ran fine after that. I did not remove the HPOP fitting springs or wafers. Oil pressure, temperature are normal. Also replaced the fuel filter and filter O rings after I started having the loss of power.

Sounds like you need to check for any exhaust leaks. Manifolds to block up pipes and doughnuts are famous for leaking.



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I checked exhaust for leaks, I checked intake for boost, I checked static fuel pressure, I replaced the fuel and air filters. Nothing helped. Then I checked dynamic fuel pressure and found that under load the primer pump was not supplying enough fuel. Replaced pump and everything is back to normal.

Thanks for the help.