> Electronic tacho is generally generated from whatever signal is
> used to fire
> ignition pulses in a petrol car, do not know how it is done in a diesel,

        You are correct. In most cars I've seen, the tach signal is derived, by the
ECM, from the signal coming from the crank shaft sensor. It's not advisible
to tap off the crank shaft sensor though since it can be quite messy.

> unless there is electronic control of the injectors. If the tacho

        Common Rail diesels, which are relatively new, do have electronic control
of the injectors and therefore probably have a crank shaft position sensor
same as gas engines. As for older diesel engines perhaps they use a pressure
sensor after the fuel pump, I'm not sure.

> signal is
> used for cruise control, then there needs to be some interlink with the
> gearbox to know what gear it is in, but there is still a problem
> if there is
> a torque converter involved.

        Correct again. Most automatics (most cars here in North America are
automatic) have an encoder on one of the output shafts, in the case of a
front wheel drive car it's usually located in the transaxle. Which gear the
transaxle is in is usually derived from a few switch inside the transaxle
(in the case of non electronicly controlled tranaxles). TTYL

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu