CA18DET Overboosting and leans out

[forpanos]

Hello everyone.!
I have a 200SX S13 from Greece with a stock CA18DET. I have an aftermarket turbo back, free flow exhaust without a cat (70mm diameter).
I recently installed a boost gauge and a wideband and i see my car boost to 0.75 bar (with 15.5 AFR) and then go down to 0.5 (with 12.8 AFR) on second gear. In third gear it boosts up to 0.9 and then as the revs go up it goes down to 0.5.
I have changed the wastegate actuator with an HKS one but it didnt solve the problem. My mechanic changed some lines but he didnt find a solution.
Here is a log from the gauge (Black: RPM, Red: Boost, Purple: AFR)
[IMG][/IMG]

Do you have any idea on what could i try?
Thank you

[R3K1355]

What fuel pump do you run?

Is the HKS actuator off eBay or is it genuine?
Do the actuator have different springs to use with it?

Is the ECU stock?

Have you read ECU fault codes?

What spark plugs?
When was the fuel filter last changed?
Have you checked the cam timing?
Have you checked for boost leaks?
Have you checked for vacuum leaks?
Do you still have the carbon canister and hot-start solenoid installed?

[forpanos]

thanks for your reply.
Stock fuel pump. Stock ECU.
Actuator is second hand but tested by my mechanic, works better than my stock. It doesnt have different springs with it.
Fuel filter changed recently. No boost leaks or vacuum leaks, checked.

Cam timing and fault codes, no we havent checked.
Spark plugs are NGK PFR6A11

Do you still have the carbon canister and hot-start solenoid installed? ' Yes i still have everything '

[forpanos]

One another thing to note. I dont want my car to overboost, it is not something i did. i want it to run like stock at 0.5-0.6 bar

[R3K1355]

Fitting the large exhaust will make the car overboost slightly as you've removed alot of restriction making the exhaust much more free flowing, you can use an adjustable actuator to lower the boost pressure back to where you want it.

Do the HKS actuator have adjustment? They usually do.

You should probably look at changing the fuel pump for a Walbro 255, the original fuel pumps are often worn out and not supplying enough fuel.

[forpanos]

it is adjustable but i want to maintain a certain boost for the whole range. if i adjust it wouldnt it spike to 0.6 lets say and then fall down to 0.4.??
If i up the boost and supply more fuel, will it stay steady? lets say something like stage 1

[R3K1355]

If you set it to 0.6 it should stay there throughout the range, if it spikes and falls to 0.4 you have a problem with one of the components.

Stage 1 is set to 1.0 Bar, the T25 can't hold that to redline though, usually slowly drops down to 0.8 Bar by 7000rpm.
Obviously you'll need a ECU chip, fuel pump and grade 7 spark plugs for stage 1 tune. A FMIC is also advisable.