99 deville starting problems

Maybe

You do realize only testing the
vehicle, will tell you the answer

Dirty connections or corroded cables. Clean and/or replace what you can on the + and - side. + to the battery and the +starter position, and especially the - from the engine to the ground The ground is VERY important to look at here, since it is a jump start that makes it go. Let us know.

Sometimes if the battery is really dead, even jumping it wont help it start up. It just sounds like a dead battery. Just try getting a new batter first then go from there.

Hello: The battery is under the rear bottom seat cushion. Please check the cable connections for corrosion and tightness. If cable bolts are bad corroded they need to be replaced. Clean all connections with battery cleaner (Auto Zone etc) You may have to replace the battery. (while working with the battery make sure the ignition key is OFF. If above doesn't correct problem have the alternator checked, again auto zone, advance auto etc.)

Sounds like a dead battery. However, I will tell you that these vehicles are very sensitive to voltage. Try cleaning the battery cables and tightening them properly.

you need to verify the dome lights are turning off before you walk away,something is draining the battery.check you car out after driving it and make sure radio and any other things all shut off.

sounds like the plugs are wet, Always replace them if you replace the upper intake manifold,

hi, can you hear a clicking noise when you turn the key to start as the starter gets its power direct from the battery so also check these wires are connected and not came loose.
If you can hear a clicking noise when you turn the key this means the starter motor needs replacing ok.
Let me know how you get on or if you need further assistance ok

the battery is located under the rear seat, check battery connections. if connections are tight replace starter.

You will need to have the battery tested, I am sure you need a new one, Kragen Auto provides free battery testing.