crankshaft sensor on 98

the middle 2 spark banks on spark generator were out, we had the spark gen and coil pickup checked, come to find out it was the crank sensor tht was bad. we changed that and the car ran fine, but here several hours later the car is nopw back to the same 2 sparks being out. this is the 3800 electranic engine. anybody got any ideas about wht the prob is