Hi All,
Smiths Motorsport (Caerbont) 100mm electronic rev counter Reads to 14k (bike engine). On the old set up it was picking up a signal from one of the two original yamaha R1 wasted spark coil primaries and seemed to be reading okay. It would rev to the limit with no load but there was an issue with the engine management causing the engine to not make it over 9k while actually driving. Was on MS2 for fuel and the Yamaha ignition module for spark.

Long story short (see the BEC section for more) but it is now on Speeduino for fuel and spark and seems to be running well (subject to final mapping). The ecu has an output for the car tacho so this is now the input signal for the rev counter. On first start up the car rev counter was showing exactly double the rpm the engine was spinning at so went to 14k when the engine was at 7k. I can halve the output pulse rate from the ecu easy enough so did this. The revs now match but now when it gets to about 8k the rev counter needle falters then drops to zero. The ecu is seeing a good signal from the crank and will go right up to the rev limiter (currently set at 11600).

Any thoughts?

Can you set the tachometer to 8 cylinders and reset the ECU?

Often when this happens the signal wire from the ecu to tacho just needs a resistor down to gnd or up to 12v depending on the ecu drive output (eg 470r)

Agree, it's likely a poor signal strength and a pull up or pull down resistor will likely help no end.

Thanks for the responses. I tried a pull up resistor (for apparently that is the direction it should be) but made no difference at all. I'm wondering whether there is a fault in the rev counter itself.