My 79 300TD is starting hard, smoking excessively, and has no power at low engine RPM. I feel these symptoms point to some air in the fuel intake. I have tried three other lift pumps from other cars that start and run well. I temporarily eliminated the cars tank/line system by placing a 2 gallon can in the engine compartment. The valves are adjusted. The injuctor nozzles test good. No excessive blow-by with the oil filler cap off. A compression test shows an even 300 lbs. on all five cyls. Of all the things I've tried, the only thing that had any effect was one of the four lift pumps made more power and a little less smoke than the others. Do I need a valve job? Should I try an injuction pump? or a re-man lift pump? Any feedback would be a plus. Thankx