So I was cranking it over the other day and as the battery power gets lower and lower the tach starts to work but only if there low voltage ....if i charge it up it doesnt work again..............WTF? But it still wont start.

I think it might be time to go back to the five minute checklist that SoCal has posted many times. Did you ever check the voltage at the fuel injectors?

Stolen from SoCal post.

Go through the five minute quick test.

Check for power at the coil and at the injectors with the key on.

No power at the coil it's the ignition switch or related wiring.

No power at the injectors it's the DME relay.

Power at the coil and injectors points to a bad reference sensor. The connector may be corroded and/or not plugged in all the way or cracked and may have broken the wires inside.

Check if the sensor is working by pulling a plug wire, inserting a spare plug, grounding the plug to the intake and cranking the engine. If there is spark then the reference sensor is working.

Could be the second set of contacts in the DME relay. These are for the fuel pump. The fuel pump should run for a half second after you stop cranking. Have someone listen for it behind the passengerside wheel well. Check the fuse for the pump too.