Digital Pulse Adjuster, Part 2

Last week in Part 1 we introduced the Digital Pulse Adjuster - a brand new modification kit that allows you to modify the behaviour of any pulsed flow control valve - including the factory boost control valve, auto trans line pressure, the valve that electronically controls power steering weight, and so on. This week we look at how the Digital Pulse Adjuster is connected to the car.

Connecting to the Car

As covered last week, the DPA intercepts the output signal from the ECU which normally drives the flow control solenoid. In this sense, ‘ECU’ stands for any Electronic Control Unit – it may be the engine ECU (turbo boost control), an auto trans controller (line pressure control), or a dedicated steering controller (power assistance weight).

But how do you actually wire it in?

The DPA has four connections – power, earth, signal in and signal out. The power and earth ones are easy – just any ignition-switched 12V source and a good ground – but what about the signal in and the signal out? In some cases this is pretty easy as well, but in other cars it can be a bit more involved.

• Most Common

Most cars drive their flow control solenoids as is shown in this diagram. One side of the solenoid is connected to 12V and the ECU switches on the solenoid by connecting the other wire to ground through a switching transistor. In this system, when you disconnect the solenoid and turn on the ignition, on one side of the plug you’ll find battery voltage (ie nominally 12V) and the other side, usually no voltage (this is the signal wire).

In this situation it’s very easy to connect the DPA. The signal wire is cut and the side going to the ECU connects to the ‘IN’ on the DPA, and the side going to the solenoid connects to the ‘OUT’ of the DPA.

However, some ECUs will realise that the solenoid is no longer connected to them. In these cases a dummy load needs to be placed across the ECU so it doesn’t know what it’s missing. This load usually takes the form of a resistor, wired as shown here. The resistor should be a 10 watt (ie big!) one of about the same resistance as the solenoid coil – often about 20 ohms. (Measure the solenoid coil resistance by connecting a multimeter across it with the multimeter set to ohms.)

This diagram shows exactly the same wiring as the diagram above, but it is laid out more like the wiring in an actual car, where both wires from the solenoid often go back to the ECU.

• Less Common

The other approach is where one side of the solenoid is grounded and the ECU switches 12V to it. In this system, you can’t make the measurements with the solenoid disconnected. Instead, you need to use a multimeter that can measure frequency (if you pick carefully, even cheap multimeters costing less than AUD$60 can do this). With the solenoid plugged-in and working (which may require driving the car), earth the negative lead of the multimeter and backprobe each connection of the solenoid in turn. On one side you’ll find a frequency, and on the other, nothing. The wire with the frequency on it is the signal wire.

In this case, both wires going to the solenoid need to be cut. One side of the solenoid is connected to ignition-switched 12V and the other to the ‘OUT’ connection of the DPA. The signal wire from the ECU goes to the DPA’s ‘IN’ terminal.

Again, a resistor might be needed so that the ECU thinks that the solenoid is still there but this time it connects to ground (remember, the other side of the solenoid originally connected to ground).

This diagram shows exactly the same wiring as the diagram above, but it is laid out more like the wiring in an actual car, where both wires from the solenoid often go back to the ECU.

Wiring Tips Note that in all cases when the DPA is installed, the solenoid has 12V on one side and the DPA ‘OUT’ connection on the other The resistor that simulates the presence of the solenoid connects from the ECU signal wire to whatever the other side of the solenoid originally went to – 12V or ground. The Signal output of the ECU always connects to the DPA ‘IN’ terminal The Signal output of the ECU can always be found by backprobing the solenoid terminals when the solenoid is actually working (car may need to be driven under load). Where a solenoid that was originally being switched to 12V has been converted to being switched to ground (the "Less Common" approach above), a change to Link 2 on the DPA always needs to be made. More on this below.

The Links

Before it can be used on a car, the Digital Pulse Adjuster needs to be configured for your particular application. This is done by positioning on-board links – three are moveable in service and two are soldered into place when the kit is being assembled. These are covered in detail in the kit instructions, so the following is just an overview so that you have an idea of what’s involved.

• Link 1 - Moveable

Link 1 is normally left in the negative position.

• Link 2 - Moveable

This link inverts the output, so it is swapped to positive if the solenoid has been altered from being switched to ground to being switched to 12V. Otherwise, its position stays the same as Link 1, ie negative.

• Link 3 – Moveable

When the DPA is adjusting an input duty cycle that is either 0 or 100 per cent, it doesn’t know how quickly to pulse the valve because normally the valve is being held fully open or shut. So what the DPA does is memorise the last frequency that it saw and use that as the valve pulse rate. Removing Link 3 causes this memorised frequency to be locked into memory. Leaving the link in place means it re-learns this frequency each time. Normally, Link 3 is removed when the system is working correctly.

• Links 4 and 5 - soldered

These reverse the way the hand controller works. Link 4 reverses the order of the load site numbers compared with input duty cycle (ie whether a 100 per cent duty cycle = 0 load site or 128 load site), while Link 5 reverses whether pressing the ‘Up’ key increases or reduces duty cycle.

Testing

A key test to show whether the DPA has been connected and configured correctly is that when it is wired into place, the car should continue to drive exactly as standard. (That’s assuming that no up/down changes in the program have been made!) If the solenoid that the DPA is controlling suddenly starts to show different behaviour, check all wiring connections to the car and if they’re fine, try swapping the position of Link 2.

After that you can start tuning the action of the solenoid!

Conclusion

While it can look a little tricky, wiring the DPA into a car always requires only four wiring connections – and two of them are power and earth! Then with the DPA installed, custom tuning of the operation of the valve can begin.

Next we install the DPA to control power steering weight and then custom-tune the steering feel across all road speeds from 0 – 200+ km/h...