If an engine is cranking slowly the first thing I would suspect is a weak battery. Remove both battery cables and clean both the cable connectors and the battery posts. Put a battery charger on the battery and charge it until if is fully charged. If the problem still persists, then suspect a starter going bad or the engine is slow in time. Remove the starter and have it tested at an auto parts store. If the starter checks OK, then you need to have the engine timing checked. If your Check Engine light is on, have the ECU scanned for a trouble code and go from there.
No of cranks used in 6 cylinder engine
You need a battery. There's a very small chance it could be something else, but from the symptoms you describe it is more than likely a bad battery.
If the engine cranks & cranks & cranks before it starts even though it's warmed up already.
Check engine compression Check engine timing
No, The compression test is done as the starter cranks the engine
Engine cranks but doesn't start.
An engine which cranks but will not start is not receiving enough fuel or has no spark. A clogged fuel filter or bad spark plugs often cause this problem.
"Check Engine" light comes on when you turn ignition switch on and should go off when engine cranks.
The engine needs fuel, compression and spark to run, it is missing one of those.
fuel filter... or throttle body
Sounds like you might have a bad starter relay.
engine cranks over but will not start.