need help from pro rotary dudes
 

So let me try and explains this extremely flippin cofusing issues im having with my mazda rx8 since it wont start.
So i got the car a couple a weeks ago, with it starting up just fine, until a week later when battery died, since it had been sitting for a long time at the previous owner. replaced it no problem. Next week i put in an A/C belt since there was none in it when i bought it.
I then proceed to try and turn on the car without success, it was really close but didnt turn over, i then waitet a little only to find out the cranking speed got slower, and slower and slower, the more i cranked. Fine i then bought a 2kw starter motor and replaced it, didnt help a bit. It still cranks really slow, and even now it smells like frikin burnt wire from the left side under the hood, im extremly confused, what the issue here is?
believe i hear the"humm" from the fuel pump in the back when putting key in run position. Checked injector fuse, fuel pump fuse, all good.
Hope someone can draw some sort of conclusion from this thank you very much on beforehand.

Is the AC compressor seized? Remove the belt again and see what happens

Be sure your terminals are clean, tight and not stretched out.
Even though the bolts bottom out they could still be loose.
Check your grounds, check to see if your plug wires aren't bunched together or arcing against something.

Have you checked the ignition coils, spark plugs at all? Number one cause of engine problems. They last about 25k miles, so consider replacement even if it's not the current problem.

It sounds like it's flooded, hold the gas pedal down while you crank, for 3 attempts, then try to start normally. Repeat. Look up "deflood procedure" for more detail. Or take out the spark plugs and clean them by hand, which also gives you a chance to evaluate if they're due, and if some are not firing at all.

Flooding is usually the result of poor ignition health. You can read up on the full story there.

it might be seized, i will try that. Can the compressor cause it to not start ?

Yes, a seized pulley can put enough drag on the starter that it won't let the engine start.

Since the starter is new, make sure that the battery is fully charged and you didn't get a bad unit (it's rare but not impossible for any part to be bad "out of the box"). If you have another car, take both to an auto parts store and they can test both.

Next, trace the wiring from the positive terminal of the battery, down across the crossmember that supports the battery and airbox, back across the left side engine mount bracket, and then to the starter. There's one thick wire (probably 2 or 4 AWG) that literally runs from the battery to one of the terminal lugs on the starter. Check for damage to the insulation or wire itself. Also, make certain that it's firmly connected at both ends and that all of your grounding straps are in good shape. The starter grounds through the transmission and engine. There's a big ground strap that connects from the LIM to the chassis near the air pump on the right side of the car as well as one or more on the crossmember supporting the battery and airbox.

Thanks for the assistance, just took off the AC belt. Cranks much better. So AC compressor is seized. Well unlucky as i am after a few cranks with good speed, the starter motor just clicks and no cranking is happening, i again just bought brand new battery yesterday aswell replaced starter motor so im fking lost sorry for my language, and yes i guess new plugs and deflood is the next step.

You've run the battery out of juice, just recharge it. That's what the clicking means.

Do this /\

Thanks man just recharged works good, now i just need to deflood, guessing it's rather simple :)

Yeah, A/C needs to be run once in a while to properly lubricate it.

If you don't need it, you can tear it out, but otherwise you might want to replace or repair it.

Just to be safe, I would check the ignition components as Loki mentioned, unless you replaced them recently already.