Any discussion about this build is going to gravitate towards
the engine management system. Its complicated and it is going to
cover a lot of this section. If you have followed the engine section
you will know that I intend to reuse the existing engine management
system. There are a few reasons for this:
1) Cost - Aftermarket systems for the M70 engine run at around £1500
2) Parts - Easier to get parts from BMW than an aftermarket company
that may not exist in five years time
3) Availability - The engine management system happily comes in
the same metal box as the engine came in!
4) Simplicity - With wiring diagrams and care, it should be trivial
to get the engine running
5) Diagnostics - By reusing most of the loom, standard BMW diagnostic
equipment will still work
A fairly active user community exists on the internet for the BMW
750 so its not that hard to find detailed information about either
the engine management system or any technical details concerning
the mechanics. I was able to get very detailed electrical schematics
and even schematic diagrams for the EML and DME.
The rest of the vehicle loom I will make myself. I think of myself
as being reasonably capable in this area, and I object to paying
almost a thousand pounds out for a loom that would require terminating
the connections anyway.
DK Motor cleaning and overhaul
|Here is one very grubby DK
Motor. The whole thing is covered in corrossion and a laquer. This
laquer yellows with age and proves difficult to remove. The throttle
housing was also full of carbon and this buildup causes the motor
to slow down and can damage the DME it is connected to if the motor
This assembly can cost as much as £1100 each brand new, yikes!
Fortunately these motors are not difficult to overhaul at home with
a basic tool kit. You need a clean working area (front room in my
case), plenty of rags, polish, 600 wet and dry paper, some degreaser,
bearing grease and plenty of patience.
When taking the unit apart, if you have a camera, take plenty of photos
to aid in reassembley. Be careful when taking it apart, make sure
you do not force anything. The only component I had trouble removing
was the spring retaining cup which was very stiff.
|Here you can see all the parts layed out
on my coffee table. The brushes are delicate so need care when handling.
The armature on the motor should have any corrosion removed carefully
with wet and dry paper. Lay the armature on the wet and dry and spin
it to remove a thin layer. Do not try to remove all the discoloration.
When done, use a scalpel or something thin and remove any debris from
between the copper contacts.
I did not remove the torx screw from the end of the wiper. By removing
the throttle butterfly plate you can dismantle this part without touching
the wiper and potentially upsetting the calibration.
When applying grease to the motor bearings, make sure to not contaminate
the brushes, you only need a small amount. You can however be quite
bold in applying grease after thoroughly cleaning the needle bearings
in the butterfly housing.
||Here is a completed motor. These have
many nooks and crannies that are difficult to clean, so its hard to
get into every place and get it really clean. Sandblasting would be
an effective way of getting the grime off, but you must be very careful
to make sure sand does not contaminate the bearings or electrical
You can test these motors by hand by twisting the sprung end of the
shaft by hand. It should spring back smartly. Do the motors one at
a time so you compare the spring tension between one you have renewed
and one you have not. The difference should be marked. It certainly
was in my case!
Alternator cleaning and overhaul
||The alternator was functioning OK, but
was again pretty dirty. Inside it was full of twigs and dried leaves,
which I thought would do little for long term reliability. So it had
to come apart.
Dismantling the alternator is quite simple, the only special tool
required being a heavy duty soldering iron to split the field windings
from the diode pack (30W or higher). The silly little soldering irons
you get free with B&Q tool kits will not cut the mustard. DO NOT
use those little blow torches you see the guys on 'American hotrod'
using. They damage insulation and cause stress fractures from rapid
extreme heating. Every time I see them using those on TV, dripping
flux and solder all over the place I am glad they havent done wiring
on my car.
The brushes were worn, but not to the point of requiring replacement.
The main bearings were free and quiet. Corrosion had taken place on
some of the electrical conductors, but this is easily fixed with fine
emery paper. The armature slip rings just required a slight clean
up but nothing major.
I managed to damage the front pulley when removing it, be careful
as its soft and easily damaged. If you do damage it, replace it. This
is because the poly belt that runs on it will wear out quickly if
running on a damaged pulley.
Fuel injectors are delicate solenoids.
They take fuel from a pressurized rail and deliver it in precise
metered amounts at specific intervals as the engine rotates.
The spray pattern of the injector should be a mist, not a dribble.
Once again cleanliness is next to godliness. And here is an image
of four injectors. The two at the top are before cleaning, the two
at the bottom obviously after.
Carburettor and injector cleaner was used to remove the crud from
the outside. The top of the injector is where clean filtered fuel
enters. It is important to make sure no crud enters this port during
your cleaning operation. I used an entire can cleaning the injectors.
New sealing rings will be applied to each injector before re-installing
them. It is fortunate that you get copious amounts of these with
the upper engine gasket set.
|This image shows the bulk of the wiring
loom. It looks fairly horrific like this, but once you start connecting
everything up again, it all starts to make a lot more sense. Parts
of the transmission control, active suspension and ABS cabling are
present in this loom and need to be removed.
The cloth backed insulation tape that is wrapped around all the cables
must be removed for you to gain access to the unused parts of the
loom. You will probably find, as was in my case, that the tape that
binds everything has deteriorated to the point where it falls off
leaving a black sticky residue over everything. I went through a fairly
large number of rubber gloves due to the fingers sticking together.
Here the fuel injectors, temperature
senders and DKM motors are wired up. By connecting everything at
this stage, you can concentrate on routing the cable where you want
it rather than where it used to go.
It is almost essential to have the donor vehicles wiring diagram.
You can buy this from BMW, but it is fairly expensive. There are
complete wiring diagrams for the 750iL on some of the peer to peer
networks, and it is one of these that I have. I printed it out and
bound it in a large ring binder. There are an awful lot of pages
so make sure you have plenty of paper and printing ink/toner!
|The temperature senders here for the inlet
manifolds have had their cables extended. You should hook these cables
up and extend them, even if you will need to extend them again when
you route the cables through to the ecu's in the passenger compartment.
This will help you from getting the cables confused at a later stage.
Anywhere a cable is exposed it must be protected, here I am using
spiral wrap. This is an SVA requirement. Not only will it make your
cables look neater, it will prevent chafing which could potentially
cause a fire. You can bind the cables together using electrical tape
if you want, but you must shroud them with spiral wrap or similair.
Where cables are joined, I have soldered them together and used heat-shrink
sleeving to cover the join. Not only will this prevent shorting out
but reinforces the joint and prevent fatique failiures. A good quality
soldering iron is essential. Try to get a low voltage professional
type such as is used in electronic assembly. Not only do they heat
up much faster than mains operated irons, the tips are of better quality
and will produce a consistently better join. Use a good quality rosin-cored
flux, and try to keep the joint steady until it hardens and cools.
Make sure you have slid a piece of heat shrink sleeving over one of
the cables before you make the join!
|This is a headlight from a Nissan 300zx.
This is the same light as used by Lamborghini in the later model Diablo's.
The small Nissan logo is obscured on the Diablo by a piece of formed
carbon fibre forming an eyebrow over the logo. This is one of a pair
of lamps I purchased off ebay 'as new'. You can see from the picture,
these lights were anything but new. For some reason, the interior
surface of lamp has been covered in a sticky backed foil. I presume
this is to increase the amount of light emitted from them. Apart from
looking awful, this lights would not appear particuarly authentic.
So they had to be stripped and cleaned of all the foil before I could
||This is the other light after cleaning.
Much more authentic looking. The lamp to be overhauled is first placed
in an oven preheated to a temperature of 150 degrees celcius for a
period of three minutes. This causes the goo which holds the glass
to the lamp body to go soft. Note that before you heat the lamp, remove
everthing you can from the unit, such as bulbs, clips and rubber parts.
Once the lamps are hot, carefully use a spatula to carefully pry the
glass from the plastic body. Once its cooled down, its pretty simple
to strip the reflectors out.
The foil left a lot of adhesive stuck to everything. I found the best
thing to remove it was Gunk engine degreaser. By careful rubbing of
the glue with a soaked cloth, you can roll the old adhesive off. Once
its removed, you can reassemble the lamp and heat it up again to reattach
the glass, or remove the sealant completely and use new sealant. I
used new sealant, a black compound usually used to seal gutters and
I will test the lamps at some point to ensure the sealant does its
job when the light gets hot.
|Fuel pumps and accelerator
|The BMW 750iL uses a drive-by-wire schema,
and so does not have conventional cable operated butterfly valves.
The throttle position is measured by a potentiometer, similair in
function to the rotary volume control on a stereo.
The original arm of the throttle potentiometer is removed and a new
longer brass bar is bolted on. This has holes along its length to
allow adjustment of the pedal throw and position. The accelerator
at rest position can be set using a stop bolt on the pedal box, the
maximum throw, by a stop fitted to the front of the bulkhead behind
Two rose joints are used to couple the throttle to the lever arm on
the potentiometer, the whole thing being secured to a small carrier
fabricated from stainless steel.
|Two fuel pumps are required for the M70
engine, one for each bank. They are mounted between the engine and
the fuel tank and are acoustically isolated from the chassis using
rubber mounting pillars. The pipes in this image are run but no wiring
to the pumps has been completed as yet. Bracketry for the pumps has
to be manufactured yourself, and this is one area that I think Parallel
could do a much better job. The supplied BMW brackets are not a good
fit inbetween the chassis rails, you can see in the image the top
and bottom brackets I have had to fabricate. This is a fiddly job
to get the pumps to suspend correctly, I was unhappy with this arrangement,
so I have split some hose pipe and applied it to the bottom of each
pump bracket to ensure that as the rubber deforms over time, nothing
metal can touch the chassis and cause vibration.
|This is the ECU's in their new home. The
original engine diagnostic socket is mounted at the back of the cabin
and will help with testing and fault diagnosis. The entire system
will be covered by the centre console. Its suprising the little space
in a car of this size there is put these sort of things. The ECU's
use the metal boxes as additional earthing points, so it essential
that the brackets they are mounted with connect to the chassis firmly.
|Here the engine is more or less complete
bar the two plastic camshaft ventilation valves and piepwork. All
of the cables are bound with electrical insulation tape, and are then
shrouded in split plastic to prevent chaffing from damaging the cables.
It also prettys everything up and make it look less untidy, which
is important given the amount of cabling this engine requires.
The middle of the engine will eventually receive a plate which will
cover over the injector cabling and the rear of the engine where the
fuel pipes and electrical connections come in.
This image shows the battery compartment.
The battery earth side is secured in three places; to the engine,
chassis and to to a remote charging/starting socket. This is a standard
connector used by such groups as the AA and RAC to connect jump
leads, the connector is placed on the rear engine bulkhead for ease
The positive lead is also run in a similair fashion and is fed to
four places; a high current feed to the starter, jump socket, permanent
feed to the engine management system and a final feed to the main
system fuse box.
At this point, the oil pressure sender and switch has not been installed,
and the cabling for the binary mode A/C switch and A/C fan have
not been run.
|This is my fusebox installation. Its a
high impact ABS box, mounted using stainless steel bar to the windscreen
bar and rear boot mid-bar.
The fusebox is an easy wire system from SVC. Its designed primarily
for Lotus Sevens, and so is missing some of the functionality required
for the Diablo replica. The extra functions are quite easy to implement,
such as the fog-lights, AC compressor and engine management functions.
I have cut the entire of the rear boot section away as I want to place
removeable panels in to make access to these places easy.
|This is my temporary dashboard. I dont
have the curved dashboard yet as it isnt finished. So I have made
this highly stylish sports style MDF dash.
This allows me to continue wiring the car and test the various sender
units until such time as the dashboard arrives.
|The dials are in the sort of correct location
here. I have spaced them further than is necessary so that I can locate
the dials in the correct place without messing about with the cabling.
All of the sender units are now connected, the only one I cannot test
yet is the speedo. I will probably jack the rear wheels off the ground
and try that just as soon as my exhaust system finally arrives.
|This is a prototype of the AC climate
control I am building. The design is split into three circuit boards.
The first holds the LED display and switches. The second contains
the microcontroller and interface chips. The third and final board
contains the power relays that emulate the switches on the Vintage
Air control panel. This design is not quite finished yet. Another
device needs to be added which emulates the slider which controls
the heater valve.
The microprocessor used is a standard PIC microcontroller running
at 4MHz. It has 4K bytes of ROM space and a handful of RAM bytes.
At the moment it is only 40% full of program code, so there is plenty
of space for added functionality.
Not all of the functions present on the original climate control panel
are available on the Vintage Air system, so I have configured the
panel to perform some different functions. What would have been the
recirculate air button, now toggles the display to the external temperature.
On the top row, another unused button is configured as a simple on/off
switch. It does not power down the microcontroller, but simply switches
off the AC, display and blower motors.
The push buttons are also illuminated and a feed from the side lights
can be used to light these up, and to also dim the LED display for
night time driving. The LED display is multiplexed, so diming is simply
achieved by leaving each individual display on for a shorter period
of time than usual.
The three small circuit boards hold chip thermistors. One is used
to check the condensor temperature, so that the condensor does not
ice up, the second is the internal temperature sensor, and the third
is for external temperature. The thermistors are not particuarly accurate,
and become less so the more extreme the temperature. Their accuracy
is approx half a degree celcius at 25 degrees celcius, getting worse
in each direction.
|These are the printed circuit boards from
the manufacturer. They are supplied on a 'biscuit' which is a cheeky
way of getting the boards cheaper as the whole set of boards only
counts as one board this way. Even so, because these are prototypes,
they are pretty expensive.
The boards are two layer and are of the same type that my company
uses to manufacture test and measurement equipment. All of the pads
are gold plated to increase resistance to corrosion, and to provide
a better quality solder joint.
The three large PCB's stack together to form a module, this is then
secured to a front panel which contains the switches and illumination.
The switches are the most expensive part and it is difficult to locate
illuminated switches which are cheaper and are of the same size and
The large board to the left is the display board, the centre one contains
the microprocessor, and the large one on the right contains all of
the power handling equipment such as the relays, voltage regulators
and heater servo control.
The three very small PCB's are for temperature sender units. One is
installed on top of the condensor inside the air conditioning unit,
another is installed inside the vehicle, and another outside. These
senders are used to determine the correct settings to apply to the
AC Systems clutch and heater servo. They will be dipped in resin to
provide enviromental protection and to allow them to get wet if they
|Here is the citroen wiper motor modified
to fit my car. I have fitted new bearings to the main shaft supplied
by Parallel for this purpose. The mechanisms wear badly here and the
wobbly shaft that results can lock up damaging the gearbox or worse
The mechanism here needs to have some material removed to make it
fit correctly from around the main spindle. The motor has also been
rotated by 180 degrees to clear the brake fluid resevoir that it sits
|This is the Fiat Coupe switch gear which
is going to be used in my car. Its not exactly the same as the Lamborghini
version and has several extra functions that will not be implemented,
such as rear wash/wipe.
The cables connected here are for the wiper mechanism above, the colour
codes listed here will work with the citroen motor and are as follows:
|| Park signal to wiper motor
|| Slow speed to wiper motor
|| Fast speed to wiper motor
|| To switched supply
|This is the AC climate control panel viewed
from the front. Here you can see how the boards stack up to make one
At the moment, the panels are not secured and the mechanical components
are missing. Primarily because these parts are not ready yet.
||This view shows the rear panel where all
the electrical connections are made.
I used spade terminals because this is what the Vintage Air system
uses. I have not fitted the connections for the heater solenoid and
the temperature senders because I have not finished the software for
this part yet.
These are some images of the intital
prototype run up on a bench power supply. The pictures are pretty
cruddy because I took them with my camera phone, but you get the
Top left image shows the unit set to display what would be the external
temperature. The dot on the top left of the LED is used to indicate
its not showing the target temperature inside the cabin.
Top right image shows the same reading after blasting the temperature
sender unit with freeze-it spray. The unit is unable to display
temperatures lower than -9 degrees celcius because there are not
enough digits available. Switching to Farenheit gives you an increased
lower end temperature display.
And to prove it is capable of displaying Farneheit, the bottom image
shows the external temperature with Farenheit mode enabled.
The software is nearing completion now. The unit can already control
the fans and air vents. All that is left is the heater servo control
and climate control algorithms to code.
|These are the headlamps after I completed
the repair process. You would never know that one of the headlamps
has been completely repainted inside. The colour required which is
a pretty good match is Peugoet metallic graphite grey from Halfords.
The reflector for the projector has also been repainted using chrome
effect paint. Its nowhere near as good as the electroless plating
used originally, but its miles better than just the unchromed plastic.
I baked the paint onto the reflector using the oven, and the light distribution is actually pretty good considering
the paint finish. Its actually closer to the finish polished aluminium
gives than actual chrome.
The left light looks a different colour because of the angle of the
lamp in the photograph, in reality you can not tell the difference in colour.
|Here on the left is the mould I have made
of the prototype front panel. Its made using RTV silicone which is
extremely good at picking up detail, can withstand very high temperatures
and is highly resistant to a wide range of resins and chemicals. A
jig will be made to hold threaded inserts in the correct position
to be embedded within casting resin.
The item on the right is the original produced from a stereolithographic
printer. It uses a two part process of resin and wax to create any
three dimensional shape. The wax is used to provide scaffolding to
hold the resin in place as it is layed down, micron by micron. When
the part has printed completely, for this part about three hours,
it is simply boiled in water to melt the wax and reveal the finished
|Here is the initial prototype with a partially
complete front panel. The buttons are mounted here and the legends
have been inserted behind the lenses. They look pretty good, although
not entirely accurate because the legends on the top and bottom left
hand side are different on the original. This is because the Vintage
Air system that the panel controls does not have as many functions
as the system in the original Diablo. In my implementation the top
left button switches the unit on and off, and the bottom left button
displays the external temperature.
||This is the first functional prototype
hot off the press so to speak. It has been bench tested and appears
to function correctly.
The flying lead protruding from the back is the compressor drive.
It does not have enough capacity to drive a clutch directly, but is
designed to drive a relay which then drives the compressor clutch
through the binary mode switch.
I will be taking this prototype to the stoneleigh show if anyone wants
to take a look, but bear in mind it is a prototype and the quality
of finish is not indicative of the finished article.
The panel will then go away for testing by Naz at Paralle Designs
to ensure the basic functionality is good before further development
work takes place, and the revision one units are constructed.
|This image shows the wiper blade in position. Its a tricky fit requiring time and patience to get right. It works on a cantilever system to completely clean the drivers side and most of the passenger side windscreen.
The hardest part with this particular part of the build was getting the front boot hinges to clear the wiper motor when the lid was either down or up. I ended up completely re-working the drivers side hinge to ensure the wiper motor would not be fouled. As it is I may need to revisit this as the front boot does not clear the wiper correctly as it is raised, so its back to the drawing board for these components.
||This is the button I have settled on for using on my centre console. It has an anodised aluminium surround so it should look reasonably like the original although the button cap is white instead of black.
As my gauge set is white this is probably a good thing. The lens cap itself is an absolute bitch to get off without the right tools. These said tools are out of stock right now so I had to use a jewellers screwdriver to prise the cap away from the surround which chews the plastic up a little.
The legend is simply carefully trimmed laser printer paper. When I actually get the whole set of switches done I will use my label printer which can trim the decals as it makes them.
Edit: It would appear that the cap is actually threaded, you dont need to prise it at all. Just twist it to unscrew it.
Here are the nine switches I will use for my console. The legends are installed in the button caps and are printed vinyl. The cigarette lighter is for scale.
The buttons in order from left to right are:
Front boot release, Dial brightness, Passenger door lock/unlock, Drivers door lock/unlock, Hazard lights, Side lights, Main beam, Interior light, Fog light.
The switches are a mix of momentary and latching variants depending on their function. The Hazard light switch is only available in momentary so I will construct a little circuit to toggle the lights on or off.
The Dial brightness switch is unused in my build, I only put it on for the sake of completeness and I will probably end up using it for some other function.
Its too wet and windy down the workshop today, one of the worst storms in a long while is sweeping across the country. So I decided to stay in the warm and figure out the wiring between the Ford Granada wing mirror motors and the Vauxhall Corsa mirror switch.
It didnt take too long, and the good news is the two systems are compatible. Here's the wiring colour codes:
Connect Brown on switch to positive supply
Connect Black on switch to ground
LH Mirror Purple to Black with Red tracer on the switch
LH Mirror Purple with Green tracer
to Yellow on switch
LH Mirror Purple with White tracer to Green on switch
RH Mirror Purple to Black with Red tracer on the switch
RH Mirror Purple with Blue tracer to Blue on the switch
RH Mirror Purple with Green tracer to Grey on the switch
The LED for wing mirror heaters can be illuminated by connecting the Black cable with a white tracer to the positive supply.
|I have almost finished all the wiring forward of the front bulkhead.
At this point all of the lights are now working, including the fog lights wired in the front bumper. I also put the side indicators on the front wings and connected them up. The only external illumination still left to deal with is the hazard lights.
You can see in this image that I have yet to finish panelling out the front boot. The headlights have no seal around them and so water can get into this area very easily. My intention is to cut holes in the bottom to let the water out, and have a watertight removable panel to stop water ingress into the luggage compartment. I will also mount the water bottle in this area as I dont fancy fiddling around with odd bits of pipe to route the water through to the bottle.
|The rear lights are pretty easy to sort out. The internal lenses have fast-on spade terminals which you simply plug your female receptacles on. The only problem is that the normal insulated terminals are a little too large to fit into the available space. You could solder direct onto the terminals, which is what I did with the steering column stalks. I didnt want to do this here as I can get the correct type of connector pretty easily.
The type required is called a flag style female fast-on connector. A separate insulation sheath is available and I installed these as well. Its essential when using crimp on connectors to use the correct tool to do the actual crimping process. Cheap crimpers can cost under a pound, whereas the set I use cost over a hundred pounds and can do a variety of different crimp types. I am fortunate where I work to have easy accessibility to high end tools like this to do the job properly.
||This is the rear of the two section dashboard assembly. The cabling is terminated into two plugs which provide power both switched and permanent live to the various instruments and illumination.
||This is the front of the dash panel. Its not finished completely yet, for instance the air vents are not snapped back into the panel as they are murder to remove again. The aluminium finishing rings are not bonded in either, they are simply prevented from falling out by the use of cable ties.
Also not fitted is the flashing alarm indicator, and the lamborghini badge which goes between the vents.
The reason I have not finished this part completely is its going to be in and out of the car over the next couple of weeks, so the opportunity for scratches and damage is high. The less I have fitted at this point the better.
The only thing I would change here is the clock. VDO who make the gauges do not have a white faced clock of the same type as the rest of the gauges. When the background illumination is on, the light shines from behind the clock rather than onto the face as with the other gauges. Its something thats not quite right, but I wont be doing anything else about.
||This is the microswitch assembly which detects when any tension is applied to the handbrake. When th handbrake is fully off, the spring is relaxed and and the electrical connection is broken. As the handbrake is applied, tension is put on the spring which activates the microswitch closing the electrical connection.
Because the lever on the microswitch is connected via a spring, the cable can be pulled further than the mechanical limit of the microswitches lever.
The spring is attached to the cable with a modified piece of choc-block electrical connector. I modified it by cutting a slot in it so that it slips over the cable. The screwdowns are tensioned lightly so that they grip the cable snuggly. They dont need to be massively tight.
||One of the final things on the dash was the installation of the air-con control panel. I had to file the aperture slightly as it was too snug a fit to get the panel in and out easily.
The three sensors are routed as follows, the condensor sensor fits through a ready made hole in the top of the air conditioning fan box. The external sensor fits anywhere in the car where it is out of the direct influence of wind. The internal sensor on a normal car would fit behind a little grille to sense the interior temperature, sometimes a little fan would drive air over it. As there is no such aperture in a Diablo, I simply fixed it to the underside of the dashboard.