1991 olds 98. sometimes engine will crank but will not start. I add a bottle of dry gas to tank and car will start after a few minutes. Do I drain tank for possible water or check for a sensor problem?
There may be water in the fuel but I kind of doubt that is the trouble. I would guess it is more likely due to a lack of fuel. Try sparying some starter fluid into the intake if you still have the trouble and see if that improves the time it takes to fire up.
Check fuel filter. Your tank may have excessive particulate (frequently rust) which is clogging up the fuel filter making it difficult to start. The car probably needs it’s entire fuel system cleaned out.
Next time you can also try pumping up the fuel pressure before starting. Turn the key to on without cranking. You should hear the fuel pump run for about 2 secs. Turn the key back off. Then back on a few times. Then see if it doesn’t start right up. If that does the trick then it likely means that the check valve that helps keep your fuel system pressurized has failed. When you turn your car off the fuel system empties back to the tank, and then the pump takes a few cycles to get fuel pressure back up.