We don’t think that it is possible to overstate the importance of this
project: an electronic kit that when built, allows full control over your car’s
mixtures by means of a digital hand controller. And you want to know the real
clincher? The kit costs just AUD$79.95. Don’t have the electronics skills to
build it? It is also available through the AutoSpeed shop, fully built and
tested.
If all you want to do is alter your car’s air/fuel ratio, expensive
interceptors are pretty well all immediately blown out of the water. Want to
change your high-load air/fuel ratio? This project can do it. Swapped in a new
airflow meter or upsized the injectors? Again this project can provide the
solution.
If your car uses a voltage-outputting airflow meter – hotwire or vane - this
interceptor will work with it. We’re talking something that is easy to tune,
absolutely seamlessly transparent in driveability, and easy to wire into place.
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 Fuel 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 Fuel Adjuster is available from Jaycar Electronics [www.jaycar.com.au] or through the
AutoSpeed shop for AUD$79.95, with the required Hand Controller kit
AUD$59.95. Built and tested
versions of the Digital Fuel Adjuster and Hand Controller are also available
from the AutoSpeed shop.
The electronics design and development of the Digital Fuel 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 particular
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 Fuel 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
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How It Works
The Digital Fuel Controller (DFA) is an interceptor. It takes the voltage
signal coming from the airflow meter and allows adjustment of this voltage up or
down in very small steps. It interpolates between the steps (ie smooths the
curve of the adjustments) and when no changes are made to the signal, the input
exactly equals the output.
The latter means that there are no ‘digital jumps’ that might give poor
drivability.
In fact, on the subject of driveability, it is brilliant – we spent over 24
months and thousands of kilometres trialling the DFA in different cars
(including the ultra-smooth 1998 Lexus LS400, a 2002 Impreza WRX, an STi Impreza
WRX, a Nissan S15 200SX, a 1988 Nissan Maxima V6 Turbo, a mid-Eighties BMW 735i
and a 1999 Toyota Prius) and if the modified air/fuel ratios are set correctly,
the drivability remains absolutely factory.
The DFA allows real time tuning, so that you can make changes with the
digital hand controller (either on the dyno or the road) and immediately assess
the results. Additionally, you can scroll through the map in non-real-time mode,
making changes as you go. Changes can be made at 128 load points that normally
correspond to 0-5 volts, the output range typical of airflow meters. (Note that
the DFA can also work on 0-12V and 0-1V signals, the latter especially good for
modifying oxygen sensor outputs. We’ll cover these aspects at another time.)
Each of the 128 load points can be adjusted up or down in 127 steps, which
gives a very fine range of adjustment indeed. The removable digital hand
controller shows both the load point being accessed and the up/down adjustment.
Tuning changes are made with pushbuttons on the hand controller – no laptop is
required.
It is brilliantly effective at altering mixtures, it’s available now, and it
is incredibly cheap.
So, how do you use it?
Tuning
The digital Hand Controller uses a two-line LCD display, eight ‘direction’
pushbuttons, a VIEW/RUN pushbutton and a RESET button. (Incidentally, the pics
of the Hand Controller shown here are of the prototype – the final kit version
differs a little in appearance.)
The hand controller 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
In RUN mode the display shows which load site is being accessed by the
running car, and what up/down changes have been made at that load site. But what
are these load sites all about, anyway?
Typically the DFA is set up for 0-5 volt signals. In these cases, an input
voltage from the airflow meter of 0 is indicated by a load site of 1 (shown on
the hand controller as “INPUT 1”), and an input of 5 volts is shown as a load
site of 128 (“INPUT 128”). From
this it’s not too hard to work out that all the in-between signal voltages will
show up as in-between load sites – for example, a signal input voltage of 2.5V
will show as a load site of 64.
For example, a particular airflow meter might have a minimum voltage output
of 1.5V at idle and a maximum voltage output of 4.6V at full load. This means
that when the car is being driven and the Hand Controller is in RUN Mode, INPUT
numbers ranging from 38 to 118 will appear on the LCD. In this example you then
have 80 load sites at which the airflow meter voltage can be adjusted (there’s
no point in adjusting load sites below 38 or above 118, because in this case
they’re never accessed).
So the INPUT load sites are just another way of showing airflow meter output
voltage.
In RUN mode you can real-time tune each load site as you’re on it. For
example, if you’ve got an assistant driving the car up a long hill and the Hand
Controller is showing load site 87 (“INPUT 87”), pushing the white ‘up’ key will
cause the mixtures to be immediately richened at that load site. Each time you
press the white ‘up’ key, the OUTPUT number shown on the display will change
upwards.
For example, the display might look like this:
OUTPUT +2 (dV)
INPUT
87 /RUN/
This shows that at load site 87, you’ve increased the voltage output of the
airflow meter by 2 units (which will cause the mixture to be richer). If you
want the mixtures to change even faster, press the black ‘up’ key, which will
cause the adjustment to jump up in blocks of four units. Pressing the ‘down’
buttons will reduce the airflow meter voltage at that load site, leaning the
mixture at that load. The maximum adjustment is plus/minus 127 units.
(The ‘dV’ to the right of the top line means ‘delta voltage’, ie change in
voltage.)
Tuning in real-time RUN mode can be useful but VIEW mode tuning is often
used. VIEW allows you to scroll left/right through all the load sites and then
make tuning adjustments.
So for example, a moment ago in real-time tuning RUN mode we set load site 87
to +2, and now we’d like to tune load site 86. By pressing the RUN/VIEW button
we can set the controller to VIEW mode, and then by pressing the left/right keys
we can move up and down the load sites, putting in any tuning figures we want.
If the car is running, these tuning figures will immediately take effect. So
after moving to load site 86 in VIEW mode and pressing the black ‘up’ button
twice, the display will look like this:
OUTPUT +2 (dV)
INPUT
86
<VIEW>
A complete tuning map might look something like the following:
Load Site |
Tuning Adjustment |
38 |
5 |
39 |
8 |
40 |
11 |
42 |
7 |
42 |
7 |
43 |
16 |
44 |
17 |
45 |
16 |
46 |
17 |
47 |
17 |
48 |
17 |
49 |
17 |
50 |
15 |
51 |
12 |
52 |
12 |
53 |
12 |
54 |
12 |
55 |
12 |
56 |
11 |
57 |
8 |
58 |
6 |
59 |
2 |
60 |
2 |
61 |
1 |
62 |
0 |
63 |
0 |
64 |
1 |
65 |
1 |
66 |
1 |
67 |
3 |
68 |
3 |
69 |
4 |
70 |
4 |
71 |
4 |
72 |
4 |
73 |
8 |
74 |
12 |
75 |
12 |
76 |
12 |
77 |
13 |
78 |
13 |
79 |
13 |
80 |
18 |
81 |
17 |
82 |
17 |
83 |
17 |
84 |
17 |
85 |
17 |
86 |
17 |
87 |
13 |
88 |
13 |
89 |
13 |
90 |
13 |
91 |
13 |
92 |
13 |
93 |
13 |
94 |
13 |
95 |
14 |
96 |
14 |
97 |
14 |
98 |
14 |
99 |
14 |
100 |
14 |
101 |
14 |
102 |
14 |
103 |
14 |
104 |
14 |
105 |
12 |
106 |
12 |
107 |
12 |
108 |
12 |
109 |
12 |
110 |
12 |
111 |
12 |
112 |
12 |
113 |
12 |
114 |
12 |
115 |
12 |
116 |
12 |
117 |
12 |
118 |
12 |
It’s easier to see what it looks like when it’s graphed.
In this case all the tuning adjustments are positive – that is, the air/fuel
ratio at all loads (except load point 62 and 63) needed to be richer. You can
see that less enrichment was needed at medium loads, but fuel was added at both
low and high loads. (This is the actual tuning map for a 1985 BMW 735i, which
doesn’t use closed loop. The tuning was done on the road using a MoTeC air/fuel
ratio meter.)
Note that unlike a programmable management system - where you’d expect the
map to be more regular in shape - the resulting air/fuel ratios from the DFA
interception are the outcome of both what the factory had already programmed and the changes that you want to make.
For example, if you want richer mixtures in the midrange than the factory had
set (eg in a turbo car as it comes on boost), there’s likely to be a hump in
your tuning chart at that point.
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Conclusion
Tuning is easy:
- There’s
a range of load sites accessed either real time (RUN) or non-real-time (VIEW)
- Up/down
tuning adjustments at each load site are made with the up/down keys
- In
VIEW mode only, the left/right keys takes the tuner through the different load
sites
In use it’s even simpler than this explanation indicates – it takes only a
few minutes for even novice tuners to get the hang of things and start tuning
the air/fuel ratios.
Next week – Set-up and install of the
Digital Fuel Adjuster
The Shortcomings
Let’s be realistic – all products and modification approaches have
shortcomings. So what are the DFA’s?
Firstly, it is an interceptor. All interceptors – no matter how fancy their
names, initials or advertising – have negatives. The most major is that the ECU
needs to be confused into doing what you want. For example, if you reduce the
load signal coming from the airflow meter, the mixtures will go leaner – but the
ignition timing is also likely to advance a bit. For this reason it is important that the
engine be monitored for detonation when the mixtures are being altered.
Secondly, you can’t change the mixtures away from 14.7:1 when the car is in
closed loop (that is, when the ECU is using the feedback of the oxygen sensor(s)
to determine mixtures). Again, that’s the same with any interceptor. (However, as mentioned
above, the DFA can be used to intercept the oxygen sensor signal – but that’s
another story. Also, when major engine management changes like injector or
airflow meters are made, the DFA can be used to bring the mixtures back into the
range of closed loop adjustment. The ability of the DFA to be able to change the
airflow meter signal across the full load range is therefore very important in
all cars.)
Finally, the DFA comes in kit form and so needs to be built. As with all
electronic kits, if you make a mistake in the construction process, it’s likely
that the DFA won’t work. (But in that case spend more money and buy a pre-built
kit.) These Pre built kits are available here in the Autospeed Shop
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The Specs
- Voltage
input: any voltage from 0 to 14.4V
- Voltage
Output: 0 to 1V, 0 to 5V or 0 to 12V plus offset
- Offset
Adjustment: +/-127 steps corresponding to 19.6mV for 5V range
- Maximum
Offset adjustment: +/- 0.5V with 1V range +/-2.5V with 5V range or +/-6V with
12V range (optional finer resolution reducing adjustment range by 5)
- Input
adjustment points: 1 to 128 corresponding to 39mV steps from 0 to 5V for 5V
range
- Input
to output response time for offset change: 5ms
- Display
update time: 250ms
- Step
up and down with 1 step per button press or at 4 changes per second if button
held
- Skip
offset adjustments: step up and down with 4 steps per button press or at 16
steps per second if button held
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