I have a '91 jetta gl 1.8L that i have used for a demo derby car(sorry guys). It ran fine for the first demo derby. then when i got it home, i go to start it and nothing. So i pulled off one plug wire to see if it has spark. It doesn't except when you first start to crank it over, it will spark once then nothing. My dad jumped some wire(not sure which one) and it will spark everytime he jumps it. I was told it could be a hall sensor. Does this sound right? or could it be the computer? checked the coil and thats fine, plugs and plug wires are good. I just can't figure it out. I'm not really a car guy, more into old chevy trucks

. Any help?