Hi guys need some help.
i have a 97 xk8, but it wont start. i just painted it and an in the process of sanding and buffing. mass air flow sensor was bad so i replaced it with one from ebay. started the car and had it running for a good time, the next day because of rain i put it in the garage, 2 days later, backed it out and was working on it, started it to put it back and it stalled, now wont start, the brother found a wire loose in the mass sensor connector, i just repaired that, tried starting the car and the air box blew off, loud bang. put it all back on and tried again, same thing. any ideas. tensioners have been changed 20.000 miles ago.

 

With a backfire of that power, I'm surprised the intake manifold did not blow off. The manifold or seals may be damaged.

You have been starting and moving the car numerous times, but probably not warming the engine up. It is probable that you have suffered bore wash by now, in which the rich mixture used in starting leaves raw gas in the cylinders if the engine is shut off cold. With the original nikasil lined engine this raw fuel removes the oil from the cylinders, resulting in low compression. It can even happen with steel liners.

One way of curing the the problem is to remove the plugs on the right bank and put about 1/4 tsp. oil in each cylinder, then replace plugs and try to start with gas pedal floored initially to shut off fuel, then easing up on pedal. Some have reported being able to start without adding oil, just shutting off fuel.