I guess I still don't get boost control...

[Corey872]

- serial number of your K-Pro: 2227

- vehicle you have: 2002 Acura RSX Type-S

- ECU you are using: K-Pro K-Series Programmable ECU

Mods: Turbonetics turbo, waste gate solenoid, waste gate

- specific description of problem: I set up boost control with the following parameters:

Enable boost on B21 - check

Max Boost at 0% duty - When the solenoid is electrically energized, boost pressure can flow to the wastegate, otherwise it is vented to atmosphere - this solenoid is normally closed.

Min duty cycle - 0%
Max duty cycle - 100%

Solenoid Activation - 4psi

Control Method - Fixed Duty Cycle 100%


Using these parameters, I make a run and hear the wastegate open at about 5psi. Data logging confirms that the max boost is steady at about 5.6psi. This fits well because the wastegate has about a 5.5psi spring. So I know the solenoid is wired right, physically working and, Kpro is controlling it.

So to start generating the Pressure / Duty Cycle numbers, I move fixed duty cycle down to 95% - boost pressure shoots up to 15psi or higher. I try 98 and 99% with the same result. Put it back to 100% and get 5.6psi.

Data logging shows the solenoid activation, but unless the duty cycle is set at 100%, it doesn't seem to limit the boost. Should I try some other settings? Could there be a problem with saturation of the solenoid coil at 100% duty cycle?

[Spunkster]

What happens at 20% duty cycle?

[Corey872]

That actually seems to work. I can hear the waste gate open and boost is limited to around 9.5psi.

I guess I am still unclear as to why this works with the setting "Max Boost at 0% duty cycle" and setting duty cycle to 100% gives me the lowest possible boost (5.5psi directly from the waste gate spring) I guess some more testing is in order on my part, but thanks for sending me in the right direction.


Also, if this boost / duty ratio holds, it seems like the curve is going to be pretty steep. Maybe a lighter waste gate spring would help, or at least one with a lower spring rate?

[Spunkster]

Boost Control Parameters
Previous Top Next

These boost control parameters determine how the ECU controls the boost control solenoid.

Enabling Boost Control


Pin A11 (unused EGR output) is used to run the boost control solenoid, as it is a duty cycle controlled output.

Solenoid Configuration


There are two types of solenoid - normally open and normally closed. A normally open solenoid (like the GM solenoid) will give maximum boost at 0% duty. Note that in this case SManager inverts the duty cycle so that in SManager 0% duty cycle is minimum boost, and 100% duty cycle is maximum boost. It is important to set a boost limit as a solenoid or wiring failure will result in maximum boost.

Duty Cycle

To control the solenoid a square wave is sent to the solenoid. Due to the impedance of the solenoid and frequency of the output this square wave results in a progressive opening (or closing) of the solenoid The solenoid will have an effective range, outside which changing the duty cycle will not affect the solenoid opening. For the GM solenoid this is 15% to 85% duty cycle, so it not recommended to operate the solenoid outside these limits.

Control Method

There are two control methods: a fixed duty output, where the solenoid is run at a fixed duty cycle and boost will be about the same in each gear, and a gear based duty cycle where boost can be varied in each gear.


A fixed duty cycle has one parameter - the duty cycle. When the settings are configured for a normally open solenoid the actual duty cycle is inverted so that a higher duty cycle will increase boost.


A gear based duty cycle uses two additional tables to determine duty cycle. First the Boost vs Gear table is used to find the target pressure for the current gear, then the Pressure vs Duty Cycle table is used to calculate the solenoid duty cycle to reach the target boost.



Solenoid activation pressure sets the point where ECU starts to use the solenoid to control boost pressure. Normally this can be set a little below the minimum boost pressure in order to minimize wear on the solenoid.

Pressure vs Duty Cycle


The Pressure vs Duty Cycle table contains a lookup of pressure valves which correspond to a solenoid duty cycle. The values for this table must be set by using a fixed duty cycle (see Control Method) and noting the resulting manifold pressure. Note that different ambient conditions will result in slightly different boost pressures for the same duty cycle.

Low/High Boost


This allows two different boost settings (by gear) to be used, based on a switch input. Typically these two boost settings would be used for wet/dry conditions, high/low octane fuel or street/drag tires.

Boost by Gear


These tables set the target boost for each gear. The pressure units are determined by the unit used for the solenoid activation pressure.

Air Temperature Compensation


The boost pressure for a given duty cycle will vary with ambient air temperature, with increased pressure with cooler air and less pressure with hotter air. This table allows you to adjust the duty cycle based on intake air temperature. The compensation is only applied when using boost by gear - the air temperature compensation is not applied to the fixed duty cycle value.

[Corey872]

Yes, I am kind of getting the hang of it now.

I guess the bottom line is I check what ever solenoid I have and Kpro sets the minimum boost to 0% and maximum boost at 100%

Thanks again for the help