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Digital Pulse Adjuster, Part 1

A brand new way of modifying car systems

by Julian Edgar

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At a glance...

  • Take control over any factory pulsed solenoid
  • Allows modification of factory boost control, auto trans line pressures, power steering weight
  • Can also be used to control an extra injector
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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 AUD$59.95.

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?

Click for larger image

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 the injector.

Click for larger image

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 [] electronics 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 Electronics [] 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 Cars.)

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.

Julian Edgar

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 little less.

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 background.

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

RUN mode:

  • view the tuning map real-time as it is accessed by the car
  • make real-time tuning changes

VIEW mode:

  • move up or down through the map, reading what tuning adjustments have been input
  • make non-real-time tuning changes

LOCK mode:

  • tuning changes are prevented but the map can be viewed
Click for larger image

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 change upwards.

For example, the display might look like this:

OUTPUT +2 (dD)

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 effect!)

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 ECU:

  • 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 uncontrolled way.
  • 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.

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