After the number of years that I've owned my 7 I have added
various switches, lamps, etc. The problem is that it had
all become a bit of a mess and I wanted to simplify the
layout and un-clutter it all.
I did some research and from a value for money point of
view Aim seemed to have the best range of all in one displays.
I few years ago I saw a seven with a Motec
dash and really liked a simplicity of having everything
displayed in one place. Unfortunately I couldn't stretch
to a Motec but Aim
had a model which was very similar in the MXL. Some more
research and there are three versions which mainly differ
in the amount of onboard memory they have. I decided that
I didn't want or need any datalogging so I was able to go
for the base model which gave me all the channels that I
would need: Revs, Road Speed, Oil Pressure, Water Temperature
and Oil Temperature plus it had built in sequential shift
lights, 6 programmable alarm lights. In addition to the
normal items (above) to display I could wire in any 0-5v
inputs I wanted and create custom sensors. This latter feature
allowed me to input my wideband sensor and display the AFR
in the 9-19 range. The software allows you to pick which
input channels you want to display and a simple page system
allows you to toggle through to the others.
The only snag was the fuel sender which is simply a variable
resistor connected to a float. One problem is that the normal
dial has built in damping, so it doesn't bounce around all
the time. The other problem is that it isn't in the form
of a voltage and so need converting. To fix the latter Andrew
at Dataspares
pointed me to info
page on their website which detailed the use of a pull-up
resistor to convert it to a 0-5v signal. To fix the latter
was a bit harder and on the bench testing with a multimeter
I could see that the signal was jumping all over the place.
During a visit from my brother for my birthday I managed
to raise the problem and he kindly sketched out a circuit
that would electrically damp the signal over a period of
time. I made up the circuit the following day and after
adjusting a resistor value to increase the time lag I was
happy with it. I tidied everything up and added it to the
pile of sensors to fit to the car.
For the new dash and switches I contacted Richard from Carbon-Bits
and got a list together for the switches I wanted (Fog,
Hazard, Wiper, Washer, Cooling Fan, Wideband, Indicators,
Flash, Main Beam and Lights). Everything arrived quickly,
Richard delivering his well known high quality service.
The project took a bit of a bit of a lull while I finished
off a living room wall building DIY project and then Christmas
followed by a new year laziness got in the way. When I did
finally get going things went pretty quickly. I ripped the
old dash apart and removed the old dials and wiring in a
day or so. I left all the old switches hanging in the loom
so I could figure out the wiring for the new one easier.
The next task was to mark out and drill the new carbon dash.
First of all I had to cut out the slot for the steering
wheel bush so I could position the dash on the car and also
give myself a reference point to measure from. I placed
a lot of masking tape on the areas that I wanted to place
my new switches and lamps. I then spent an evening in front
of the TV with a square and marked out all the positions,
allowing for the chassis tubes that would be behind the
top and bottom edges. I got a tip from Mark to use a step
drill and so I managed to borrow one and in one evening
I made all the holes. I used a cutting disc in a dremel
to make a slot for the dash connector to poke through. Job
done - I had been very nervous of cracking the dash, but
it was very easy as long as you take your time.
Once all the holes had been cut I was ready to stick it
in place. I got some black silicone sealant for this job
and put a very generous bead along the top edge and loads
in the radius along the bottom. I then positioned it and
wrapped masking tape all over it to keep it in place.
While this was setting I made a start of cutting out some
of the unwanted wires. I found I could get rid of a lot
of the red/white cables that feed the bulbs for all the
gauges, plus the black grounds that go with them. Also for
the chop were a lot of green power wires that feed all the
gauges and some of the lamps. After a few hours the silicone
had almost gone off (although I left the tape on for a another
day to be sure) and I started to position the new switches
and figure out the wiring. Most of the switches were straightforward
but there were a couple of exceptions. The Hazard and Wiper
were the two which weren't - the Hazard was simple to wire
but because I was changing the lamp to an LED I had to add
a couple a couple of diodes into the wiring for the indicator
switch along with rerouting the one of the feeds from one
of the relays. The Wiper was a bit more tricky and it required
a call back to Richard to get the correct configuration
as it is effectively 3 independent switches in one to ensure
that power is maintained to allow the wipers to park.
Once all the switches were in place the next job was to
fix the MXL in place and to figure out the wiring. I made
up a spreadsheet for the connections
that I thought I needed and sent this off to Andrew at Dataspares
who kindly had a look and confirmed I had most of it right,
but suggested using a 12v from the dash to feed the oil
pressure and fuel sender. Making up the loom was simple
enough although the pins are very tiny!
After a quick test to confirm all the switches worked I
was able to refit wiper motor followed by the scuttle and
then finally the screen. The next job was to configure the
dash to suit all the sensors and this is done by assigning
the channels and then deciding where you want them displayed
and if you want any alarms to be assigned to a high or low
value (such as oil pressure, AFR, etc).Setup
Screen
The final job was to drain the fuel tank and calibrate it
using the voltage reading on the dash - (some
instructions). For this I simply unbolted the fuel line
from the pressure regulator and directed it into a Jerry
can placed on a box to get it at the right height. To get
the fuel pump running I had to ground pin 20 of the ECU
plug as the ECU had been sent away at this point (see K3
upgrade). I then created my custom sensor that would
read 0 to 5000mV exactly as it received it from the sender
unit circuit. When I was finally ready to start adding fuel
to the tank I thought I had better just check that the readout
was working correctly. So, I unbolted the sender from the
tank and tried moving the float. Oh dear - I didn't get
any change on the dash, that wasn't right, it remained hovering
at 500mV. I did some poking about under the dash to check
it was all plugged in OK and everything was as it should
be. At this point my mood descended into my 'this isn't
fair' depression and I resigned myself to having to pull
most of the dash area again to find the problem. I removed
the heater blanking plate to gain a little access to the
back of the wiring and find my nicely protected circuit.
I pulled this apart. I then started testing various voltages
to make sure the Op-Amp was getting 12V and that the ground
was OK. They were and it was. Next I tried removing the
plug from the dash and seeing if maybe was getting a rouge
signal. It stopped reading, which meant it was coming from
somewhere. I then gave up putting off the inevitable and
climbed upside down into the driver seat, knees over the
rollbar and chin wedged under the steering wheel - oh joy.
I stripped back the wired which I had neatly encased in
some heat shrink and again checked for 12V. I also stripped
back the signal wire and found a point that I could measure
this from. At this point I measured ~1500mV. This was different
to the reading on the dash so I really started to wonder
what was going on. I got out of the car and moved the fuel
sender and re-measured and sure enough it was changing (so
the timer circuit was working as well). I reread my wiring
diagram and it all made sense so I then looked at the user
manual for the dash to check I was looking at the connections
right. I spotted that the pin I was using related to channel
5 and something in my brain clicked. To make use of a 12v
output from the dash I had swapped the oil pressure and
fuel levels onto different channels from my original configuration.
I hopped over to the laptop which was plugged into the dash
and checked and sure enough, channel 4 was set for fuel
while in reality I had wired it into channel 6 - so I was
seeing the output from one of the other channels (AFR I
think). It took all of 20 seconds to re-select the channels
and put them on the right inputs and upload it to the dash.
Hey presto, everything was now working perfectly. All I
had to do now was tidy up the mess I had made of my nice
neat loom during the last 3hrs. I left this for the next
day. So, back to the calibration. This was easy enough,
if a little boring and smelly with all the fumes. I could
only get a 1/2lt jug to my filler so I ended up measuring
after every top-up so I could plot a finer graph and select
which points I wanted to use - at this point I didn't know
what the graph would look like. So, 3 hours later and after
two trips to the local BP station I had a brimmed fuel tank
and a graph of voltage verses amount entered. I put in about
5lts before it registered anything and it stopped registering
2.5lts from the top of the tank, which I presume is the
float hard up against the underside of the tank. I then
went inside and played with the results to produce a new
custom sensor
which mapped the voltages against a percentage of a full
tank. This will read 100% for the first couple of liters
and when it shows 0 I will have about 5lts before the pump
can't pull anymore out. I will add an alarm to the fuel
channel for about 10% I think and see how it goes.
That was it - easy really, but quite good fun. I am very
pleased with the result and intend to fit no more switches
directly to the dash to keep it simple in design/layout.
I have already added a new switch for the map switching
on the K3 ECU, but I have
done this out of sight using the old heater control cable
position.
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