91 vert starter wierdness and performance question
 

new deep cycle high amp battery, new alternator putting out 13.25 volts and my car still wont start if i let it sit for more than a couple of days.
i put the new battery in drove it for 3 days let it sit for 3 more then wha wha wha wha... nothing! took the battery in to be tested and they said it was at full strenght so i popped the clutch drove for 20 min. started it again then went home, next morning same thing.
so i have 4 theories, tell me what you think.
1) the starter motor is weak or failing or the solenoid is pooping out.
2)i have a battery drain that i dont know about and it is sapping my battery (but that doesnt make sense because it does this with a full charged battery too).
3)vapor locked?
4)bad connection between battery and starter?

also i got under my car today and found a big round hole (size of a quarter) on the bottom of the bell housing of the tranny and i could see right up to the fly wheel or whatever it is called that the starter shoots out and grips on to.
it didnt have threads like a bolt was missing so i am wondering if this is supposed to be open like that or should it be plugged and could this have anything to do with my starter issues?

ok also i have a question about backfiring and popping when i decellerate and change gears fast at high rpm.
is this a sensor issue or vacuum or what?
it is not super bad but it is obviously not supposed to be popping and back firing.
also i am getting bad gas mileage, is there something i can check or maintain to get better gas mileage? (like 14 miles to the gallon)
thanx
corey

First of all, is the starter motor turning at all? If so then its probably the starter about to die. If the solenoid was bad, nothing would happen. If you have a weak connection, probably nothing would happen. Its definitely not the battery. I recommend that you pull the starter off and take it to an auto parts plate to have it checked. They can tell you if its running slow or anything.

I think the hole is supposed to be there, though there might be something that pops in there to cover it. Its been there since I got my car, and I haven't had any problems.

As for the backfiring, does your car have a cat and emissions systems? I would think so since you are in Cali. If so, then something in the emissions system is bad, maybe the ACV. There is a diagnosis section for this in the Haynes manual. It is very normal for an emissions free rotary to backfire in those situations, but normally the cats and such prevent this. For the mileage, do a full tune-up: air filter, spark plugs, etc. You might as well replace the 02 sensor too, but to doesn't really make that much difference, maybe a couple mpg. Also, if you romp on it a lot thats really not that bad mileage. I get 17-18 in spirited driving.

cool, thanks sideways!

Keep a multimeter in your car and measure voltage at the battery when you get these symptoms of not starting. I would just change the starter. It will shit on you soon anyways.