[Doubledip]

the 1K / 3K trick works on the later model ECU's (LS1,E38,E40)

make sure you have one end of the resistor onto ignition the other onto the tacho wire...

the 4CYL bit is only if the tacho output has not been adjusted in the ECU, but will make no difference if the tacho is not registering at all..

you can get the tacho modified to work but is rather costly compared to buying a 10cent resistor and fitting yourself.