Hey guys, i did some searching and found a lot of dead threads that never really had a clear cut answer, and thought it would be best to start over listing out my exact setup.

I have a 91 N/A with an S5 JDM TII Swap. I have a 3" downpipe going to a stock exhaust, with a custom intake. I have a Trust FMIC and other then that everything is stock. I hooked a boost gauge up to see what kind of boost i was making, expecting somewhere in the 8-10 range, and to my suprise i found i was making just barely 5psi.... Now i did some research and got a few leads, but no exact answers.

I have a perfect idle, so i refuse to believe i have a vacuum pressure issues, my wastegate actuator appears to be hooked up just fine and im running a stock blow off valve which is hooked up just fine.. I want to write it off as my stock exhaust being too restrictive, but then again i think its stock and at stock it should make 8psi at least..

I'm worried that as i do more mods i will still never get my pull boost

Any ideas guys?

 

The stock wastegate spring(set at 5.5lbs) is the same as an s4. The s5 had some kind of controller to let the boost go to 7.5-8lbs of boost. I wonder if you JDM one has the boost controller removed and had a custom one in its prev vehicle. Look in the FSM to see where the stock boost controller is and see if you have one. Maybe someone else will chime in with a pic.


You should also port the wastegate if you haven't already.

 

its an N/A so i dont have the service manual..

 

Are you using the NA harness? Did you swap out the 6port injector connector for the BCS connector?

Also did you hook up the BCS vacuum line to the TID?

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/using-s5-n-engine-harness-tii-conversion-600241/

 

I did reuse the N/A harness, admittedly i didnt do the swap myself, can anyone give some advice as to how i can check these things?

 

You did say that the rod is connected to the flapper properly? The little C clip will deteriorate and the rod will come off, @ 5 lbs max.
The S5 has a boost solenoid on the top left rack. Check the pressure hose going to the wastegate dashpot, and there will be a hose coming from there up to the solenoid, then to the air intake. The ecu will open/close the solenoid quickly to bleed off the pressure to the dashpot so as the boost increases. Just get a MBC and run the hose to the controller then to the dashpot. do away with the solenoid, and adjust the boost accordingly. With the factory setup you can crank the boost up as high as you want, or at least as high as the electronics will accept without destroying the engine.

 

Swapping an S5 TII into an S5 NA chassis with the S5 NA engine management harness is simple. These are the wiring differences:

ECU pin out differences:
2M: NA - VDI Solenoid, Turbo - Knock Sensor

3R: NA - 6PI Solenoid, Turbo - Turbo duty Solenoid

The turbo duty solenoid is a bleed-type boost controller that is operated by the ECU. It is what allows the S5 TII to reach 7.5 psi instead of 5.5 psi.

You should have the 6PI solenoid plug (brown) plugged into the turbo duty solenoid (located on the oil filler neck). If not, you will only be reaching 5.5 psi due to the wastegate spring. See FSM page F1-7 for the S5 NA vacuum/solenoid diagram. See FSM page F2-7 for the S5 Turbo vacuum/solenoid diagram.

For future reference, you should refer to the S5 TII FSM sections for the majority of engine related issues. Wiring issues like this will require looking at both S5 FSM sections.