Boost (WGS) Settings


Boost (WGS)

ECMLink's boost control functions are modeled after the factory implementation provided by Mitsubishi on 1995+ DSMs and Lancer EVOs.  The idea is to start with a base duty cycle curve that fairly closely produces the desired boost and then let the ECU do some minor error correction to keep things in line.

The idea is not to just dial in a desired boost and let the ECU try to achieve it for you.  You won't be happy with the results.  Your boost pressure will either spike too high or take too long to build or oscillate too much.

Instead, you want to start with a good base duty cycle table and then let the ECU fine tune from there.

ECMLink has a helper function in the datalog tab's right click menu (called Set boost tables) that will get your base tables setup pretty well once you have manually configured the Base Duty Cycle table to be in the area you want to work in.  More details on this function will be provided on our support wiki.

Solenoid selection

It may seem simple to grab a solenoid and wire it up.  But there are a LOT of considerations you have to keep in mind.  Not only does the solenoid have to be electrically compatible with the ECU's drivers, but the solenoid has to operate properly under high pressure conditions.

The ECU expects the solenoid to provide around 28-33 Ohms resistance.  If you use a solenoid with too little resistance (or draws too much current under any condition), you run the risk of blowing the ECU's internal driver.  The "typical" GM BCS, for example, will blow the 1990-1997 ECU's BCS driver if wired straight to the ECU.  You have to wire a big series resistor and, possibly, a protection diode across the BCS pins to prevent damage to our ECUs when running the GM BCS.

The factory EGR and fuel pressure solenoids are options, but do not seem to work properly above 20psi.  These solenoids either hang open or get locked closed (depending on configuration) under high boost conditions, making them unsuitable for this application.

The factory boost control solenoid (BCS) does actually work, but it's only a 2-port solenoid.  Which means you'll need to wire it up with a restrictor (we've found that a 0.025" restrictor works well) similar to the stock configuration and you'll need to remove the internal restrictor found in the stock BCS itself.  The one advantage here is that you can plug the solenoid directly into the factory harness without need for cutting and soldering wires into place.   You'll just spend some time locating an appropriate restrictor "pill" from somewhere.  These are probably readily available, though.  Just search for "EVO" boost pills or something similar.

The one 3-port solenoid that we've tested to work well without any modification or restrictor setup is made by Ingersoll-Rand.  It's Aro model number P251SS-012-D.  You can find this solenoid on Grainger's site by searching for that part number or Grainer's part number SJJ52.  Or we'll have this solenoid available on our website bundled with appropriate 1/8" NPT nipples to go to 3/16" vacuum lines.

You typically wire the solenoid directly to factory BCS wires.  You can use the ECU Wiring Information page on our wiki for details if you need them, but you basically just locate the factory BCS wires under the hood and cut/solder/heatshrink your new solenoid into place.  Using a stock BCS does have the advantage of plugging directly into the harness.

Typical configuration

How you physically install your boost control solenoid depends on which type of wastegate actuator you have and how you want to run it (direct vs. bleeder).  Details on this will be covered on our wiki.

Logging support

There are several log values available for working with the Boost tab.  These include the following.

Technical details

The ECU's WGS output is fixed at 17hz (period of 0.06 seconds).

A "duty cycle" here refers to how much of each 0.06-second period is considered "active" versus "deactive".  A duty cycle (DC) of 100%, for example, just means the output is always active (tied to ground).  Likewise, a DC of 0% just means it's always deactive (the output is floating).

Values between these two extremes indicate how long the output is held active before being deactivated during each 0.06-second interval.  A DC of 75%, for example, means the output will be tied to ground (active) for 0.75 * 0.06 = 0.045 seconds and then switched off (deactive) for the remaining 0.015 seconds, then switched on again for 0.045 seconds and switched off again for 0.015 seconds, etc.

This provides a relatively smooth analog approximation to a variable value using an on-off solenoid and a digital output from the ECU.  Digital outputs and simple solenoid air valves are much less expensive than analog alternatives and provide reasonable approximations.