My lancer 1991 does not start, I changed the battery and the starter but the problem remains
Any suggestion?

With the new starter motor installed, does the engine crank? First, check all under-hood and under-dash fuses with a test light or multi-meter. Second, check for any codes being thrown. Third, check for spark. Fourth, turn the ignition switch to ON and listen for the whine of the fuel pump in the gas tank.

Thanks for the answer, but I forgot to tell that the starter krank but only a bit, and sometimes it even starts. The car starts always with a little push.

1. Clean the battery terminals and connections.
2. Ensure the battery is fully charged.
3. Clean the connections going to the starter solenoid. If this doesn't solve the problem, you need to replace the starter with new one.