FD rx7 will not rev pass 4k rpm HELP!
 

I just bought a 94 FD rx7 with a blown motor. Just finish swapping the new motor in today, took it for a drive everything seem fine until i tried to rev it pass 4K rpm the car break up really bad and doesn't want to rev anymore. It idle and rev to 7k rpm fine if im standing still. The car has a PFC for an ecu. Any help?

Have you checked your rev limiter on your PFC?

What are your mods? What else did you change during the engine install?

First place I would look is the secondary injectors.

This was exactly what I was thinking.

When I bought the car it didn't come with a commander or data logit so there no way for me to check it. But it rev fine when I'm in neutral or standing still

What did you change when you swapped the motor in? You said it was a new motor?

I did not change anything else on the motor it is running a parallel(none sequential stock twin turbo) one of the gear sensor on the transmission is broken off can that cause it?

So you swapped all your components from the original motor to the new motor?

the only difference is the omp older version to the newer jdm one. Its weird how it only does it when the car is moving. Rev and idle fine standing still.

A Power fc won't throw any codes or limp mode so your best bet is to get a commander and see whats going on with the sensors.

Secondary injectors are not activated during free rev while stationary, only under load @ around 4K rpm.

Another thing to check is the map sensor hose, verify it is connected to an actual vacuum source. Secondary injectors will not be triggered if the map sensor is not seeing any load change

A commander would provide all this information in one glance.

The map sensor is definitely connected to a vacuum source. I know the secondary injector is not stuck close because I tried to power it via a 9v battery and it click. I Just don't know if it actually being fire by the ecu under load at 4k. Would you recommend the commander or data logit? I was thinking of switching the whole system out to a haltech or a link g4 since I'm more familiar with those. 350-400whp is what I'm looking to get time attack build

Check them for 12v and then check continuity to the ecu, make sure your harness didn't get damaged during the engine swap

a used commander is cheap and a good thing to have for a monitoring device regardless of having a datalogit for tuning. You do not want to have to drive around with laptop all the time just to see what is going on with the ECU.

Changing the ecu is up to you.

I'll do that and report back. And I'll look into buying a used commander anyone have one for sale please pm me

That's almost the same as the 7 I'm working on a while ago, except mine can never rev pass 4K rpm, no matter what I do/did/replace

at the end it was the wiring harness, I had to run like 20 new wires all over, omfg it was horrible :(

My harness is pretty old. I hope it is not the problem. Which wires did you have to run

Do a continuity test on all the major sensors from the connector back to the ecu.

I changed my spark plug the car ran a lot better i can rev pass 4k with much hesitation. But this only lasted 5 miles or so then the plug foul again! I think my Ignition system is weak. I just bought all brand new coils! It just a stock 13b running 7psi! Is the rotary igntion system that bad? How can i improve it without going ls1 or Ign1a coils?

Injector could be stuck open.