Ok, I just finished putting in a new engine into my RX, it runs great up to 4000RPM then its cuts out and sputters and almost dies, it refuses to go over this RPM. Anyone have any Ideas on the problem and a fix? thanks for any help

 

It's pretty apparant that your secondary injectors aren't coming online.
OR- you have very bad compression- OR your cat is clogged (if you have one)

I'm guessing it's probably your secondary injectors.
Check the plugs, and check the ground from under the intake manifold, to the firewall. Actually, run a new one anyways- a heavier gauge. That ground is crap, and usually lead to the 3800 rpm problem.

I would check the voltage on those injectors by the ECU harness.
It's under the passenger floor mat- it's easy to get to, and easy to check the voltages.

Do two things. Check the voltage with a multimeter from the o2 sensor while driving. (I can't remeber which pin- the #'s are at www.fc3s.org)If it drops below .70 V when power cuts out- it's leaning out. meaning no fuel.

Second, check the seondary injector voltages at the harness, they should drop from about 13V to 11, at 3800 RPMS... and should drop farther the highre RPMS you get (more duty cycle on injector)

If you determine it's the injectors, then see where the wiring problem is (plugs, at ECU, in wires, grounding... etc)
Good luck!
Dan