Wiring Up A Fuel Computer - Discussion Thread.

[Robsey]

This thread is for discussing any queries or comments about the thread found here.

viewtopic.php?f=15&t=16628

I will also link it to other threads regarding the physical installation of the fuel / board computer.

[Robsey]

Some of the location and fitting information is discussed in this thread.

viewtopic.php?f=15&t=16611

[James McGrath]

Cool stuff Rob.
I want to add a fuel computer to my Diplomat one day. You would have thought a late 1993 Diplomat would have the yellow plug all ready but nope.

[Robsey]

Wow, that does surprise me.

All the luxury of leather upholstery, alloy wheels and air conditioning... and they don't allow a fuel computer to be fitted.

Vauxhall at it's most crazy.

[Robsey]

It is really obvious how to do it,

But is there enough interest for me to give details for wiring in a wiper stalk with board computer buttons from an Astra-G, Vectra-B or Omega-B.?

The hint is - You need to splice into three of the five wires from the standard Cavalier computer switch.

UPDATE - I have added the wiring details for stalk buttons.

[dorsetdave]

Just something I was pondering. Does anyone know if the harness connecting the display module to the main loom is the same on other GM models? If so it widen the scope for me finding one!

[Robsey]

I presume you mean the dual info display.
Time and Temperature.

In a strange twist, the dual info display is not mentioned in any GM literature (TIS2000 / GlobalTIS), and it is not shown in the schematic / wiring diagrams in Haynes, AutoData or any other publications.

All the above only show the analogue clock or fuel computer.

As for GM looms, I did think anything LS and above from 1994, but James' comment about his diplomat makes me think that GM fitted whatever "2nd Option" took their fancy.

My LS did not have the wiring for an analogue clock. Very strange.

[James McGrath]

As for GM looms, I did think anything LS and above from 1994, but James' comment about his diplomat makes me think that GM fitted whatever "2nd Option" took their fancy.

My Diplomat was made in Germany and not Luton, so that may be the cause of the anomaly.
It was first registered in August 1993 and it came with an analogue clock from the factory.

[Tobias_CDX]

If it came with the dual info display then wiring for bord computer would be prepared. But with just the clock? I don't know. Did you have look at the diagnosis connector for pin D?

[Robsey]

If it came with the dual info display then wiring for bord computer would be prepared. But with just the clock? I don't know. Did you have look at the diagnosis connector for pin D?

I would agree.
Check your diagnostic socket for a wire on pin D.


It makes sense for the car to have wiring for the board computer if it has dual info display.

The dual info display already has: -
Battery Live
Ignition Live
Illumination (Dimmable).
Temperature Sensor
Temperatute Sensor Return
Road Speed / Speed Pulse.
Ground.

Extra wires are: -
Fuel Tank Sensor
Injector Pulse Sensor

Diagnostic Plug D
Diagnostic Plug G

5 x Control Switch Wires.

The Analogue clock only has 3 wires.
Battery Live
Illumination (Not Dimmable)
Ground.

[Robsey]

If adding wiring from scratch, it may be easier to wire direct, rather than via X6.

To be honest, this is what I did.
A total sin, but I cut the main loom behind the glove box and soldered my switch wires directly to the loom.
Saved me looking for a CD spec loom and extricating the necessary loom wires and connectors.

If I was as OCD back then, as I am now, then I would have made a bespoke floor loom to suit.

The other addition that I did was to splice in three more wires for an Omega estate wiper stalk with variable wiper delay and the two computer buttons.

[Robsey]

If you have an analogue clock, you will have to add wiring for the temperature sensor.

There may be a fat, flat connector tied up against the bulkhead comprising what appears to be 6 cylinders, of which only two are populated with wires. The blue wire and the blue/white wire for the temperature sensor.

Overall wiring additions from Analogue to Computer would be.

2 x Temperature sensor wires to the under-side, passenger side corner of the front bumper.

Blue/red speed pulse wire from the radio pin 5, instrument pin 3 or from one of the small square sockets in the driver's footwell.

Red/white - injector pulse wire from the little square connectors in the driver's footwell.

Brown/white - diagnostic wire from diagnostic socket pin G orsimilar signal source, or from one of the small square sockets in the driver's footwell.

Brown/blue self test wire to diagnostic socket pin D.

Black ignition live wire from radio pin 2

Grey/green - Illumination wire. The computer isn't dazzlingly bright, so you could just take a non-dimming feed from a dash panel switch.

A dimming feed would need to be fed from the instrument cluster or light dimmer switch.

Blue/black - fuel tank contents wire would be available from the X6 connector or the instrument cluster.

Then 5 x switch wires.

[Robsey]

As part of my diagnostics thread updates, I came across information about the board computer.

The board computer testing and calibration is "briefly" described in the diagnostics / flash codes thread, but I think it would be best placed to add full instructions and guidance notes to the How2 thread in the link in the first post instead.

A message to James,
When you asked me at VauxFest 2018 whether I would like my fuel / board computer callibrating with Tech 1 following the programming to the correct code index..

You will be glad that I said no.
For one thing the process requires you to connect a resistor and switch unit to the fuel tank sender connector under the car, and also some jiggery pokery with the fuel gauge connector.

Not really something to be done in the middle of a field - lol.

[Cavalier342]

Not really something to be done in the middle of a field - lol.

It is if you have the right tools for it lol

[Robsey]

Not really something to be done in the middle of a field - lol.

It is if you have the right tools for it lol

It would have to be a set of ramps under the rear wheels, to access the tank sender connector pins.

Anyway - thankfully for me, I still have a fair few miles in the tank after the computer reaches zero on the range.

Saves any unexpected surprises.

[iangsi]

When I fitted the DID to my 93 Motorsport ( basically an LS ) it came with the analog clock, when I pulled the clock out I had the yellow plug for the board computer but not the plug for the DID I had to splice it into the wiring for the board computer fortunately the same colour cables do the same jobs for both devices. So I think you'll either have one or the other of the plugs not both.

[Tobias_CDX]

Depending on model year. Clock / BC or DID / BC. Or both without pre-installec BC wiring.