Backfiring, no power in 740 Turbo

My first thought is to check the timing belt. If it has jumped the symptoms you describe make a lot of sense.

To check it, remove the upper part of the timing belt cover. Use a socket on the crankshaft bolt to turn the crank until the timing marks line up on TDC. The cam sprocket at the top of the belt should line up with its timing marks, or be 180 degrees out. If 180 out, you will want to rotate the crank another 360 degrees clockwise to verify the timing.

The good news is that the engine you have is non-interference; timing belt failure does not damage the engine. It also is not terribly hard to replace, which translates to more modest labor costs to replace. If the belt has jumped, it is not going to work at all very much longer.

Mike