Fuel used ouput & VK Calais Electronic Dash

[VK Calais]

Hi, I have a VK Calais with an M800 running the engine, and I would like to try and get the trip computer working on the electronic dash. Originally the dash just used the injector pulse on the 6cyl to calculate its reading.

I have used a 1K ohm resistor for the 12v pullup on the tacho ouput, can I do the same with the fuel used output to attach it to the original injector input and then play with the calibration number to get it to work?

Any help would be greatly appreciated.

Cheers,
Brent

[Scott@FP]

If its similar to BMW/Audi then no, it uses both the frequency and PW to determine 'torque' and fuel usage. First step is to find out exactly what type of signal the OEM dash uses, then see if it might be possible to use an output to duplicate it.

[VK Calais]

Thanks, I didn't think about that to start with. The EFI 6cyl (bosch K-Jetronic) dash used the injector pulse from 1 half of the group fire injector bank for its calculations, and the V8 dash used a fuel flow sensor in the fuel line to the carburettor.
The signal for both engines is connected to the same pin on the instruments. I have just disassembled a factory v8 dash that I had spare and found that there are three jumpers internally on the input board, 1: FSC, 2:8Cyl, 3:MPH. Jumpers 1 and 2 have links on them.
I think the dash in my car at the moment was an original 6cyl dash which I added the link to for 8cyl, so I will dismantle it and see if there is a link on the FSC jumper, if not i'm hoping that FSC is the option for Fuel flow sensor and if that is the case the m800 should be able to drive that, I hope.

[VK Calais]

I have checked the instrument cluster in the car now and it only has the link on the 8cyl option that I have fitted myself. I have been searching online and also through the original Holden VK Service manual and other than pinouts and wiring diagrams, there's no technical info on the instrument cluster.
The schematic I have of the fuel flow sensor appears to be a photo transistor style (standard fuel flow sensor from the '80s). The sensor has a 5v supply from the cluster and the output side pulls to ground. I just powered up the cluster on the bench and the flow sensor input pin is also sitting at 5v.
I might take a chance and add the FSC link and connect the pin to the fuel used output of the m800 and play with the numbers.

[Hoolio]

If as you say the 6cyl instrument setup used the injector pulse, the most straightforward solution ought to be to setup an M800 output to mimic that. I assume that the VK works the same way as BMWs of the same era, which send an output pulse which is a little shorter than the actual injector pulse. This is probably the injector base pulse width (i.e. actual pulse take injector dead time) from which the instrument cluster can calculate fuel flow.

Why not setup an aux out table using RPM and Fuel Base Pulse Width as the axes? You need to do the maths so that at each table value the output duty is the same as the duty of the base pulse width. The instrument cluster won't care what the frequency is, since it makes its calculation from the duty of the signal.

If you are using OE injectors and fuel pressure you ought to get correct readings from the trip computer. If not, you could scale your table values.

[Scott@FP]

Any auxout is at a fixed frequency.

[VK Calais]

So can one of the m800 outputs simulate a fuel flow sensor using the fuel used setting?

[Allan]

can't use the factory fuel flow sensor?