Kouki S14a SR with S15 Injectors & ECU

[LoSt180]

Question: How does the boost curve behave on a standard S15 sr20det?

Details: I currently have a 98 S14a SR20DET running with S15 Injectors and ECU. After lots of wiring diagram comparisons, I only had to swap 2 pins at the ECU connector for the wastegate solenoid and VTC solenoid. Setup is using S14 ignition system. The wiring is correct because the component inspection procedure in the FSM checks out as good. There are also no codes in the ECU via Consult connection.

The last piece of the puzzle is wastegate valve control solenoid behavior. With the S14 ECU, boost would quickly build when I floor it and hold around 11-12 lbs (~600 mmHg per my Kouki gauge pod). With the S15 ECU, boost is only around 7 lbs (400 mmHG) until around 5800 RPM, then it builds up to 11-12 lbs until redline. So I'm only getting high boost at the top end. Is this the default behavior of an S15, or is there a difference in S14a/S15 wastegate solenoids that I've missed?

[LoSt180]

Just an update: I thought I found the issue. A document on the Nistune site (http://nistune.com/docs/Nistune%20Boost%20Control.pdf) seemed to indicate that the S14 solenoid is 39 ohms, while the S15 solenoid is 32 ohms. My hunch was that the S14 solenoid isn't responding fast enough for the S15 ECU duty cycle.

I picked up a MAC solenoid that the document recommended as a suitable factory replacement. I should've checked my solenoid before ordering, but my S14 solenoid is actually 32ohms, MAC is 27. Installed the MAC solenoid anyway temporarily, test drive had exact same behavior (low boost until 5800 RPM, then BLAM hi-boost). So I'm guessing this is just how the S15 operates. Who knew the S14 actually feels more responsive.

[Kingtal0n]

My question is why are you fooling with the OEM solenoid and not an alternative controller?

If you enjoy playing with electronics design and implement your own EBC.
Its on my list as well.

[LoSt180]

Well, I seem to have solved this issue for now by installing an HKS wastegate actuator. First I measured the stock actuator and set the HKS to the same length, this provided a stock 7psi base pressure (solenoid unplugged). It also has the same behavior of boost creep at the higher RPMs. After cooling down, I tightened to rod 2 turns to set the base pressure to about 8psi. Now with solenoid connected it jumps and holds about 12.5psi through the rev range. So much more responsive now.

I'm using the OEM Kouki DIN boost gauge, so my psi conversion might be a little off. Basically the stock base pressure is right on the line (350 mm hg), so I set the HKS around 450. Full boost now is just below the max of 700 mm hg, so about 600-650.

The main difference with the HKS is that boost is now constant, instead of building higher closer to redline.

[Hoffman5982]

I know you've solved this, but I wanted to share that my s14 SR does the boost creep thing as well. Tried two different actuators and had the same response. 6-7 psi and then 11. Even with a MBC it will do the same. Before I fine tuned it I would get 10psi, and then at 5800 it would spike as high as 15-17. Really annoying