c36 missfires at 4000rpm???????

[mercmike32]

Hey, I have a 1996 c36 with 140k miles. I changed the crankshaft pulley to a lightweight one. Now my mechanic said the car will misfire then it will go away due to the lightweight pulley, which it did. I put the stock crankshaft pulley and still no luck, so now it has the lightweight pulley back on it. Then I accidentally took out the ECU without disconnecting the battery. Then the misfires started to happen. I have checked the timing over and over, I changed the spark plugs and the ignition coils no luck. Any ideas from what may cause the misfire.