i have my acwell 5000 series digi dash wired with the tacho wire joined with a solderd joint to the coil 1-4 neg trigger from my ecu (basicly conected to 1 of the 2 coils) with 1rev 1p setting,

my read out of revs on the dash are good but i get odd half second spikes of higher revs now and then from 3500 to 7200
i have the capacator fitted on the + feed to the center pin on the zetec coil for suppression and the ecu data log is showing no issues ecu side and the car is running fine.

anyone had same issue and found how to cure it?

Stick a diode in!

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tachometer diodes [/img]

a diode is not the issue as im using 1rev 1pip setteing on the acewell of one of the coils in the twin pack

my rev counter is set read 1 pip every 360 deg so i need no circuitry like you woud use to run a std tacho of a twin coil setup.

i have fixed issue now by simply adding a single 330ohm 250mA resistor in the line from the neg trigger off the 1&4 cyl coil.
my signel was either to strong for the acwell or more than likeley i was intermittently picking up back feed off the other coil or somthing else so adding some attenuation with a resistor helped my problem.