i am having some problems with my car. sometimes when i start it after letting it sit for a day or so it starts right up. after the car is shut off after running it does not want to start back up. sometimes when i try to start it right after shutting it off it will start right up but anything more than a few minutes it wont start..it just keeps cranking. when i give it a jump it fires right up...i cant figure out why. its getting fuel and spark.
my battery voltage with the car running is 13.0 volts (turbo b16). do u guys think its too low? i know on some vehicles around 13v is acceptable. my battery light never came on. can it be the alternator causing this or what can it be? bad ground? if so where should i start?

thanks

 

Best thing to do is this following:
1. Clean electrical grounds around in your engine bay, all of them. You might want to clean your positive connections to your fuse box as well. Scrub the connectors nice and shiny, the bolts, the washers, and especially in between washers that are attached to bolts, the holes the bolts screw into, but do NOT scrape any paint off!
2. Get a multimeter. With that multimeter, use the ohms function and measure the ground resistance from various points in the engine bay to the battery negative terminal. If the resistance is higher than 0.2ohms, somewhere along the line, the connections definitely should be cleaned/repaired since the resistance should be about 0ohms. Don't forget to clean the battery ground cable!
3. Assuming you're not in a high crime area, when you stop driving for the day, pop the hood but keep it closed (down but unlocked) then the next time you're ready to drive the car (next day or five days later, what ever) get the multimeter out and raise the hood to check the battery voltage, report back the battery voltage. The reason I tell you to pop the hood the day you're done driving the car and not the day you feel like working on it is because you don't want to drain the battery ever so slightly by opening the door/unlocking, which turns on dome light etc. just prior to you checking its 'resting' voltage.

4. If you find your battery voltage is below 12v, you could just replace the battery and see if your alternator charging voltage increases to above 13.5v. However that is the (Laziest solution) and I don't like it because I'd rather fix than replace things. If you can, either take the battery to autozone to have them charge it (lazy solution) or buy a 3 stage 'smart' battery charger and charge that sucker (best solution in my opinion). Through my limited experience (about 1 week's worth) I find the "Batteryminder" series of chargers to be the best since they have a 'desulfate function' built into them. If the battery voltage is less than 12.2 despite doing a 'full charge', then it means your battery is likely sulfated and or the electrolyte is 'stratified'. I don't like using autozone to charge batteries because they always 'cook' the batteries with their high amperage charging which sort of encourages you to buy a new battery.

 

The alternator is most likely bad.

Also, you MUST provide all pertinent information about your car and engine. Failure to do so may result in thread closure.

 

13 volts is too low, should be about 14.1 running

Test the voltage with the key on and then running.

By the way 13 volts will not turn on the battery light.