I recently had my stock 13B rebuilt in my 1990 convertible and currently have racked up about 1600 miles on it. My low end power seems to be coming in fine but once i break about 5500 rpm it seems to all go away. The only aftermarket products on the motor are a Racing beat header w/ 2.5 inch piping and flowmaster mufflers. Please help!

 

Have you tried this? It may help.
I have this hesitation whenever I accelerate right around 3500-4000 RPM
The dreaded 3800 RPM hesitation is cause 90% of the time by poor ground connections between the engine, the battery, and the car. Clean or replace all the under hood ground connections. Some people have also claimed replacing/regrounding the pressure sensor's ground wire has helped. If there is still a problem after that, look at cleaning the fuel injectors and (on a N/A) that your 5th/6th ports are operating correctly.

 

Thanks! I'll jump on that tonight and see if i can work the kinks out of it.

 

NO!!! check for vac leaks. the 3800 rpm hesitation is very distinct. I've had it before. It comes and goes BY 4,000 rpms. If the car pulls strong untill about 5,000 and then seems to slightly hick up and fall off power in the middle and come on and then fall off again, just enough to slightly jerk your head a little, make sure your intake is sealed EVERYWHERE before the mas airflow meter. Power does not "fall off" when 5th and 6th ports don't open, it simply does not exist. It runs as thought the car has much smaller ports, because it does. RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR..........I'M A DUMB ***!.......!