Discussion and questions related to the course Boost Control
Hello, we are currently trying to solve a problem with a subaru impreza 2008 sti. The boost target is lower than the number on the table, also the measured boost is lower than the boost target. We looked at the compensation tables on the wastegate to control boost but no change is applied during steady state test at 4500 rpm.
Whan cn we do to diagnose the problem, where to look?
What ECU are you using?
What is your engine spec, target boosts and achieved boosts?
Internal or external wastegate?
Stock subaru ECU, target boost is 17.5 psi. High flow intake, turb back exhaust with high flow cat, 3 port solenoid valve for wastegate. I´m almost certain because the client changed the solenoid we need to retune the boost target maps, wastegate duty cycle but I don really understand how the 3 port solenoid valve works. Attached you will se some log info about the run, steady stat
Boost error is around 4 to 6 PSI.
You won't need to re-tune your boost target maps unless you want to change your targeted boost.
If you are undershooting on the stock Subaru ECU you should look at your wastegate duty cycles, you need to look at the 'max wastegate duty cycle' table and increase the values, your currently only using 37.25%, there is a huge scope for adjustment there.
On a 3 port solenoid the higher the duty cycle more boost?
That sounds correct fgallego. The solenoid is pulsed at a fixed frequency, so increasing the duty cycle of this fixed pulse width will cause the solenoid to divert the charged air away from the actuator of the wastegate thereby keeping it closed to increase the boost pressure. Vice versa, the lower the duty cycle you operate the solenoid valve at would flow more of the charge air to the actuator of the wastegate to open it thereby regulating/lowering the boost pressure.