JK Tacho On My Diesel

[jp]

I have just purchased one of them original looking tacho's from JK to fill my 3rd hole and was assuming as the instruction says you can take a supply from your w-connector on your alternator this isn't going to be any different from a diesel vehicle than that of a petrol? Its just the instructions says for petrol engines no mention of us sensible people that put derv lumps in the back Surely an alternator is an alternator regardless of what is spinning it.

Cheers

 

[Trikky2]

Electic rev counters normally got their signal from the points or ignition system. This is why the better ones had settings to cope with four, six and eight cylinder engines.

With diesels one had to have cable operated or a magnet and sensor set in the flywheel or some similar "get round".

Later the alternator based ones were developed as the electronics got cheaper and diesels became more popular in cars. Such a rev counter cannot simply be swapped to any vehicle.

It has to be calibrated, since different pulleys will spin the alternator at different speeds compared to the actual engine speed.

The JK one I can see in their online catalogue would appear to be ignition triggered and will therefor not work off an alternator.

 

[jp]

Hmmm interesting the leaflet that came with it def says to connect one of the wire to the w-terminal on the alternator. Makes sense what you say about the pulleys on the alternator meaning different results... looks like I may have to gut the internals of my new dial and replace with internals from the donor vehicle the engine came from which I have set up in my glove box atm

Though the scale will be all wrong then :?

 

[Trikky2]

The easiest way to check would be to check the rpm with something else to compare the two at the same time. For instance there are small hand held units that garages may have which require only a white blob on the engine pulley to give a reading.