What determines how long car cranks before starting?

[supernova87a]

I've got a medium old bmw, and when I turn the key, sometimes it starts right away, sometimes it takes 2 seconds of cranking before turning over. This will happen whether the engine is hot or cold, just stopped or sitting for days.

Anyone know why this is?

 

[Brutuskend]

Fuel delivery is one factor, spark is another. (plug spark / how hot it is...and how well tuned you engine is)

 

[Viperoni]

Basically the general condition of the engine.
My 86 Parisienne takes at about 2 seconds of cranking when its cold, but when its hot it always instantly starts up.

 

[CraigRT]

I know on my old 86 Celebrity it was fuel delivery.. there was a slight leak in the fuel rail (MPFI 2.8 V6) and the gas would leak out causing it to crank for a while on startup because the pump had to re-pressurize the line.. when the rail was replaced and new injectors put in, it started within 1 second or so every time.
hot or cold.

in your case since it's sporatic i am not 100% sure. as the car gets older, more quirks come about.. don't worry about it unless there are signs of some sort of failure or break down...

 

[Brutuskend]

my VW before I put in electronic ignition.....20 sec or so....now BANG starts right off the bat, so ignition is a major factor. But like I said earlier so is fuel, and how well it is getting vaporized.

 

[MajesticMoose]

my 90 civic always takes about 2 full seconds of cranking no matter how hot or cold it is.

m00se

 

[PsychoAndy]

battery power contributes to the problem. if your battery is slightly weakened, it takes a bit longer for the all the juice to flow

 

[Migroo]

For my car heat determines how long it takes to start.

Cold = about 2 seconds
Hot = about 0.421067 seconds

Its a 3 year old Civic with 16000 miles on it. (Low mileage because I live in the UK )

 

[Pikachu]

If it's fuel injected, it may need more spark. Our van had low voltage to the ignition due to corroded terminals on some relays, which caused it to crank a while before starting.

If it's a normally aspirated carburetor, the choke may not be closed fully due to sticking.

Could be fuel pump takes a while to get the fuel to the cylinders.

 

[BigLance]

Fuel !

Carburated engines generally have a harder time starting quickly because FI will auto adjust to match the condition of the motor... When the motor is cold (I dont mean cold outsite, just hasnt been running cold) things have to be pretty right on to get it to fire, to lean or to rich can cause it to crank longer..

Basically these guys have already covered the reasons why ...

 

[Zenmervolt]

<<medium old bmw>>

If it's among the older BMW's that had mechanical injection (aka BOSCH K-Jetronic) then this may just be a quirk. My sister's 1982 320i has K-Jet and it seems to pick and choose how long it takes before it starts. It always starts and it runs very well, though it does not like to idle when it's cold (in the winter you have to start it just like a carbbed car). My Accord used to pick and choose when it wanted to start, sometimes taking up to 10 minutes of on-off cranking. After changing the plugs, wires and the distributor cap/rotor (which did turn out to be cracked), I finally changed the fuel pump relay and this cured things. Probably just a quirk in your case though, since it's not taking excessive time to start. Good luck with it though.

Zenmervolt