I have a 1993 500SEL. I installed a new electrical engine harness because the old one fell apart. Now I am having a problem with no power. I can't get more than 2500 rpm out of the car. If I floor the car it goes to 2500 rpm and then stalls out. It sounds like it is starving for gas or air. Every now and then it won't start, it backfires and smells like it's flooded. There's a four prong plug at the front of the motor,it seems that it goes on any number of ways. Could you please help