Hotwire ECU speedo input.

[jenand40]

I am fitting a hotwire EFI system to my Triumph Stag, replacing the Flapper type system fitted at present.

I would like to fit the speedo sensor input to pin 6 of the ECU, on reading the details in Rave I see that the voltage pulses from the sensor are filtered by a buffer within the speedometer. I obviously do not have the correct speedometer containing this buffer and am concerned about sending unfiltered voltage pulses direct to the ECU.

Can anyone tell me what this buffer consists of and can I make one up?

Any help would be appreciated.

Thanks.

jenand40

[P38RRman]

Bit confused by this - do you now actually have a Range Rover V8 engine fitted in your Stag ?

However there are several companies who build modules which will convert (various) ECU voltage levels/pulses into tach (and speedo) signals etc (albeit for a price !)

[FridgeFreezer]

For that amount of faffing I'd megasquirt it, then you don't have to play tricks or bodge it, and there's less wiring. In fact, you could just swap in the hotwire fuel injectors and keep the rest of the flapper loom, binning the AFM & resistor pack & overrun fuel shutoff relay... speak to Nigel at Megasquirt-V8 for your forum discount!

The hotwire diagram I have doesn't show any filtering, item 10 being the speed sensor:

[jenand40]

Thanks chaps for your replies.

When I restored my Stag 15 years ago I fitted an SD1 3.5 engine with the Flapper EFI system. This has given trouble free service during that time, and having recently finished work, I wanted a project to do, and seeing as I already had the Hotwire system, I thought I would fit that. The circuit diagram shown above does show the speed transducer feeding directly into the ECU, but when I read the Rave manual it states that the signal is fed to a buffer, within the speedo, before going to the ECU. Obviously I do not want to feed this signal into the ECU and cause any damage, hence the question.

[P38RRman]

It basically depends on just what they mean by 'buffering' - this may simply be a (broad) reference to a voltage change/conversion process, or it could mean the actual (digital/analogue) conversion of pulses (per mile) from the speed sensor/transducer to the speedo gauge itself.(?)

Just google 'speedo tach. converter' for details of the modules available to convert such pulses to speedo output, typically $100... Commonly used for engine swaps/kit cars and the like (but you may need to know the specific details on the sensor signal to match it up properly of course)