I own a 94 Lumina APV, it has 163,000 miles, recently stalled and wouldn't start, taken to mechanic and later after being able to start van, developed severe piston slap and extermely loud lifter noise, now the van backfires through the throttle body upon acceleration, and when cruising along at any speed attempting to accelerate or climbing any grade will bring on severe clatter from the engine and no power, almost as if the timing is out, and it backfires constantly through the acceleration, took it to another mechanic he said the oil pump was faulty and replaced it, this did nothing to cure the problem, he also said that the engine threw a rod or something to that effect and the engine was shot, but I can get it going to 80MPH, it takes a while even with all the clattering, had a code pulled on it and a code 54 low fuel pump circuit voltage came up and it is running real lean. I am not going to dump a motor if it is something that can be repaired for about the same cost. Also had a problem with disappearing antifreeze, never could figure out where it would go, the temp would spike up I would add antifreeze and again it would disappear no white smoke or milky oil though, could all these things be related somehow?? any help or suggestions would be appreciated Thank You