Matrix user forums

does anyone have recommendations on noise immunity for pic micros in an automotive enviroment, had a project that i designed for a friend that reads the frequency of the 4.5v hall effect distributor referance signal and converted it twice a second to engine rpms, works great on the bench and works great in driveway but going down the road it freezes or starts reading odd numbers, i provided some recommendations based on past experiences like putting a logic buffer between dref and pic, pull down resistors in key places, staged cap values, sheilding the dref wire, possibly putting a audio noise filter on the power supply from the cigarette lighter, ect.....but i think it would be wiser for me to ask you guys what you think is happening? im about 2000 miles away from the test car, i tryed it on my car with different calculations of course and it works great on mine but not on his, was wondering if there is a set of guidelines to go by for special high voltage noise application to get smooth glitch free operation from the pic micro, thanks