Tach Now Going Bananas

[Elroy Jetson]

1994 325i Convertible, 5 speed continues to baffle me. The car has a persistent stumble from 2500-3500 rpm but runs well and on all 6 above and below this range. Now, when the engine is running at 4000 rpm, the tach will jump from 4000 to 6000 rpm with no corresponding increase in engine speed and the car will buck like crazy -- like it's hitting the rev limiter. The stomp test comes back with no errors. The Peake tool gives indications of bad coils at #2 and #5 (the coils are fine - swapped them into other cylinders and the problem stayed with 2 and 5) and bad Crank sensor. Listening with a stethoscope reveals that the #2 and #5 injectors are not opening in the 25-3500 range though they are operational above and below. All the connectors are tight. All the grounds are clean and tight -- unless I'm missing one (I've checked and cleaned the ground at the front of the fuel rail, behind the right shock tower, on the forward front fender and under the dash). Thought the ECU had gone crazy - replaced it with a used one with no improvement. Before I undergo the pure joy of swapping out the crank sensor, does anyone have any better ideas? Has anyone else had a similar problem? Does anyone know the German equivalent of 'Christine?' Thanks.