hi everybody, thankyou about your advice.
I have the simple problem like the previous problem.
I already made a simple counter use AT89C51 24PC with 7segment display.
I use dry cells to supply my circuit with 7805 regulator.
first step:
I start my counter circuit, the cicuit is working properly.
second step:
I connect a cable to the spark (A to spark, B no connect).
then I start the engine.
third step:
I put the end of cable (B) and I bring near the my circuit (not touch the circuit, near only) and the result is my circuit not working.

The problem like this is first to my experiment.
so would you like to give me some information to improve my experiment.
I am sorry to try writing english as good as possible.

thankyou verymuch.

hen.