I am no expert.... But it is a $3 uC....I do find it curious that you are using the analog inputs for pulse counting. You might want to use the digital inputs for all but the fuel level signal. I have read some things about noise on the analog inputs, and having invalid data when changing from output mode to input mode (not your case I suppose).
Certainly the use of analogRead is unusual - digitalRead is more likely the right thing. You're still polling though. Alternatively, people often use interrupts when reading RPM or speed in this kind of situation.