How does a trip computer work?

[Speedy88]

Looking at this:



Does it calculate mpg using the rate of fuel flow and somehow getting an output from the speedo? I'm a little confused as to how it works.

[macplaxton]

The main unit is a de-luxe calculator.

There's a fuel flow meter that installs in the fuel line that spins around and give a pulse signal for the rate of fuel flowing.

There's a set of magnets which are wired round a driveshaft coupling and a pick-up that is fixed near them, so it gets a pulse signal for the speed of car.

I can't remember which model it is, but it's a re-badged Zemco unit from memory. I had a similar unit - a Zemco ZT4, re-badged for Unipart - in an Austin Maxi I had. Still got it somewhere (I think).

I've not seen one for a fuel injection model, but I'd assume it would have a different fuel flow metering arrangement?

A non-Volvo one might be easier to find. There were various ones around back in the day:
Zemco did a ZT3 & ZT4 amongst others.
Mobelec did one called a Maximiser (and Maximiser II). There was also a Mobelec GasFax. Both were similar to the
Smiths one.
Sparkrite did one Voyager, with "ICE WARNING DETECTOR"

any more variations on the above were probably just clones.

[Speedy88]

Thanks, I'll keep an eye out for those. Surely to tell the speed it would have to be 300 specific though (for the exact diameter of the shaft). I'll take a look.

[macplaxton]

No it's universal, as when first fitted, you calibrate it.

[Chris_C]

Yup, FI has a different wotsit, instead of a whirry thing in the fuel line it has electrics that piggy back the duty cycle of the injectors.

I have an injecty thing here I've been meaning to make some copies of as there was some interest a while back, but standard Chris timescales apply. These as ever can be sped up by someone fixing Fake for me