There were some known issues with the MS2 Extra neon decoder. Get the latest beta (18 right now), and it will work fine. Also, i'm still unclear why so many want to use the VR input instead of the normal opto isolator tach input circuits. The crank sensor is a Hall effect sensor, which is NOT a VR sensor. The Hall sensor outputs a digital 0-5V waveform, that works fine with the basic digital logic circuits like the MS chip. The opto circuits have a capacitor on the input side, and also one on the output side to the chip..shouldnt be any issues with noise. If anything, make sure you have good ground signal at the crank sensor's ground wire, and also good voltage at the sensor's power supply wire. The sensor just switches ground, so this is very important. You can try this updated circuit if you wish:



Instead of the 150 ohm resistor, use a 470 ohm. Remove R12. Put the one leg of the 470 ohm resistor on the RIGHT side of R12(you can also put the 470 ohm resistor IN PLACE of R12, just make sure to get the 5 volts to the top side(left side in the diagram) of the resistor. Increase the .001uf cap(C12) with a .1uf cap. You dont need those diodes on the input side, you are basically going right around them(leave them out). If you STILL have noise, it may be worth feeding the crank sensor's power with a separate 12 volt switched line(again, from the battery), using a 10k ohm resistor in line to it. It's possible there is some noise on the 8 volt supply from the stock ECU. Also make sure you have the MS grounds coming straight from the battery, and also switched 12 volts through a relay, right from the battery(battery acts as a noise filter). Make sure you have good chassis to battery grounds, and also a good battery to block ground. You should also run a ground from the battery to the crank sensor's ground wire( you are basically running new power and ground to the crank sensor, so be sure to cut and insulate the car side of the sensor wires, and connect your power and grounds to the sensor side of the cut wires).

13.5 @108 MPH-2.2 60ft(stupid FWD!)
S16G @ 18 PSI/FMIC/Running on MegaSquirt II (Now with sequential
fuel injection)
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