The Digital Pulse Adjuster kit represents a brand new way of modifying
electronic car systems. Or to put it another way, systems which before could not
easily be modified now fall into the Do-It-Yourself class. But what sort of
systems, then? Try electronically-controlled auto trans line pressures, factory
turbo boost control, electronically adjustable power steering weight, idle speed
– in fact, anything which uses an electronically pulsed control valve.
And the cost? The kit is just AUD$79.95 with the Hand Controller another
The Digital Pulse Adjuster takes over the driving of the valve and uses both
the original control instructions and the tuning changes made by the modifier to
control the way the valve works. The Digital Pulse Adjuster is an interceptor.
So how is it different from a normal interceptor – for example, a fuel
interceptor that modifies the signal coming from the airflow meter?
Here’s the way in which a normal fuel interceptor works – it slots into place
between the airflow meter and the ECU, changing the input signals to the ECU. As
a result of receiving modified information, the ECU changes its output signal to
And here’s the way in which the Digital Pulse Adjuster works. It is wired
into place between the ECU output and the solenoid, takes the ECU output signals
and then modifies them to suit. Doing it this way has a number of major
advantages (see ‘Advantages?’ breakout below) but the main one is that it’s easy
to alter the action of just the valve you’re interested in.
The Background Story
So how did this kit come about? It’s worth briefly backgrounding its genesis,
if only so that you know what has gone into it.
The Digital Pulse Adjuster was developed and designed by Silicon Chip
magazine. The kit, along with many others, is covered in the Silicon Chip
publication – Performance Electronics for Cars – which is available from Silicon
Chip Publications or the AutoSpeed shop. The book is a must-have for DIY
modifiers. The kit for the Digital Pulse Adjuster is available from Jaycar
or through the AutoSpeed shop.
The electronics design and development of the Digital Pulse Adjuster was
carried out by the brilliant and modest electronics engineer John Clarke, while
I came up with the concept and did all the on-car development. (During this
period I wore a different hat to an AutoSpeed contributor, working for Silicon
Chip Publications as a freelance contributor to Performance Electronics for
The unusual mixture of ingredients – development funding from an electronics
magazine, design and development by an electronics guru with no interest in
modifying cars, and concept development and project management by me – has
resulted in something of which I am very proud. It’s a unique product that works
superbly and undercuts by a huge amount similar commercial products... none of
which, AFAIK, can do all that this one can, anyway!
So by no means should the Digital Pulse Adjuster be seen as an
AutoSpeed-developed project, but at the same time I am happy that AutoSpeed
endorses it and promotes it.
Flow Control Valves
Flow control valves in car systems consist of a coil, a return spring and the
valve. The opening of the valve is controlled by what is called a pulse width
modulation signal. (You may know it by its more widely used name: a variable
duty cycle signal.)
Unlike an injector, which is either completely open (power on) or completely
closed (power off), these flow control valves vary in their opening. This is
achieved by quickly pulsing the current supply to the valve. If it is on for
only half of the time (ie it has a duty cycle of 50 per cent) the coil will
'see' only half battery voltage, and so will not fully open against the spring.
If the duty cycle is reduced to, say, 30 per cent, then the valve will open a
In normal operation, the ECU pulses the valve with a wide range of different
duty cycles. At 0 per cent duty cycle the valve is fully shut, while at 100 per
cent duty cycle the valve is fully open. There’s not a lot of point in the
factory installing one of these valves and having it only open or shut, so in
all cases there are lots of in-between duty cycles used to give in-between
degrees of valve opening.
The Digital Pulse Adjuster (DPA) takes these valve control duty cycle signals
from the ECU, then adds or subtracts duty cycle from them before driving the
valve with the modified signal. For example, if the maximum duty cycle that the
standard valve ever saw was 65 per cent, the DPA can be used to add another 10
per cent, making the valve open wider. All the 45 per cent duty cycles from the
ECU can be turned into 50 per cent duty cycles, and all the 25 per cent duty
cycles can be reduced to 10 per cent.
Basically, the DPA allows you to adjust up or down all the duty
cycles coming from the ECU. In fact, you can even change a 0 per cent duty cycle
into a 100 per cent duty cycle and vice versa...
To allow you to tune the duty cycles very finely, the full duty cycle range
from 0-100 per cent has been split up into 128 tuneable ‘load sites’. Load site
1 is equivalent to 0 per cent duty cycle and load point 128 equals 100 per cent
duty cycle. In use you tune the different load sites, rather than worrying about
duty cycles – but it’s important that you know what’s going on in the
100 per cent duty cycle = open or shut?
In this story we have assumed that 100 per cent duty cycle results in the
valve fully open. However, that depends on the way in which the valve is plumbed
– sometimes 100 per cent means it is fully shut. Either way, 0 and 100 per cent
are the extremes of openness and shutness!
Tuning with the Hand Controller
The Digital Pulse Adjuster uses the same operating logic as the Digital Fuel
Adjuster, covered at
The Digital Fuel Adjuster, Part 1. In fact, it uses the same digital Hand
Controller. The controller can be plugged-in during tuning and then removed, or
left connected so that you can see the action of the mapping as you drive along.
(Note these pics show a prototype version of the Hand Controller – the kit
version looks a little different.)
The Hand Controller uses a two-line LCD display, eight ‘direction’
pushbuttons, a VIEW/RUN pushbutton and a RESET button.
It can be set to three different modes. RUN and VIEW modes are selected with
a pushbutton on the hand controller, while LOCK mode is selected with a switch
on the main unit
- view the tuning map real-time as it is accessed by the car
- make real-time tuning changes
- move up or down through the map, reading what tuning adjustments have been
- make non-real-time tuning changes
- tuning changes are prevented but the map can be viewed
In RUN mode the display shows which load site (ie input duty cycle) is being
accessed by the running car, and what up/down changes have been made at that
load site. In this way you can easily see the range of tuning load sites which
are available. For example, when connected to a power steering weight control
valve, load site numbers from 36 – 110 might come up on the Hand Controller.
Those are the load sites that are available to be tuned. They are shown on the
Hand Controller as INPUT numbers.
So the INPUT load sites are just another way of showing the duty cycle signal
coming out of the ECU.
In RUN mode you can real-time tune each load site as you’re on it. For
example, you’re using the DPA to modify the action of the factory boost control
valve. Just as the engine comes onto boost, the Hand Controller shows load site
32 ("INPUT 32"). Pushing the white ‘up’ key will cause the duty cycle
controlling the valve at this load site to be changed real-time. Each time you
press the white ‘up’ key, the OUTPUT number shown on the display will also
For example, the display might look like this:
OUTPUT +2 (dD)
INPUT 32 /RUN/
This shows that at load site 32, you’ve increased the duty cycle controlling
the valve by 2 units. So, what change did that cause? Depending on the way in
which the system works in that particular car, you might find that the car comes
onto boost a bit harder at that point – or perhaps the opposite occurs. If the
effect is what you want, keep adding in change. If it isn’t what you want,
reverse the direction of change.
In this sort of situation you will normally swap back into VIEW non-real-time
tuning. For example, if you found that a +2 correction at load site 32 ("INPUT
32") gave improved boost performance, you might want to put in a tuning increase
at all the nearby load sites as well. By pressing the RUN/VIEW button you can
set the controller to VIEW mode, and then by pressing the left/right keys you
can move up and down the load sites, putting in any tuning figures you want.
(Note that if the car is running, these tuning figures will immediately take
So in this case having got a positive result at load site 32 with your +2
change, you could select load sites 29, 30, 31, 33 and 34 and adjust each of
those up by 2 units as well. By then test driving the car, you can see the
result of these tuning changes.
Pressing the recessed RESET button (use a pointy tool to do this) for more
than 4 seconds will reset all tuning changes back to zero – that is, the map of
tuning values is lost.
By making small changes and then testing until you get a ‘feel’ for which
changes in which direction give the outcomes you want, it is easy to tune the
action of the boost control valve, power steering weight control valve, auto
trans line pressure control valve – in fact, as we said at the beginning, any
pulsed control valve!
Next week: how the DPA connects to a car
There are a number of advantages of intercepting the signal after the
- The tuning changes that you make don’t cause unwanted changes to occur in
other systems. For example, if the DPA is used to modify the action of the
boost control valve, only boost with be changed. But if an interceptor is used
on an ECU input like the MAP sensor, along with boost other aspects like
air/fuel ratio and ignition timing are likely to be also altered in an
- It doesn’t matter how many inputs there are into the ECU’s decision-making
process. Even if the ECU controls the solenoid valve on the basis of five
different inputs (eg from load, intake air temp, throttle position, coolant temp
and a MAP sensor), the use of the interceptor after the ECU still allows the
signal to be altered. Furthermore, the final solenoid control signal can still
be based on all of the original inputs (plus your modifications!).
- There is a direct relationship between modification and outcome. When you
alter the way in which a flow valve is pulsed, you know that the changes
in flow that you have programmed are happening. You are directly controlling
that valve, so there’s no guessing as to whether this input or
that input will best cause a change in output.