What is the normal voltage on startup?

[tomsh96]

Hi,

I would like to ask what is the normal voltage on startup? According to the OBC hidden menu my E46 330i only gets 9v on startup. Isn't that too low? I started noticing misfires in the last autumn when the temperature started to get colder. Can a bad battery cause misfires on startup? After ~30 sec it disappears. I changed all my plugs, CCV and hoses, found no cracks on the intake boots.

[MarcoZandrini]

Are you saying the voltage as shown by the OBC is 9VDC when you're starting he engine? That's way low. You're battery is likely bad.

[TonyAngel]

The battery should hold around 10.8v under load and around 13.7 or so while running. 12.7v or so just sitting.

[tomsh96]

Yes the OBC shows 9.x on startup. I tested my friends 20i and it was the same, but it started with no problems (btw his battery is bigger aH). My OBC showed 12.5 while sitting and it decreased to 9.x when I started cranking

[MIKYZZ4]

Engine off 12.4~12.7v
Engine running 13.5~14.5v

[90turbo1]

so you are asking what the battery voltage while cranking the engine should be on dash?

the starter will and can draw upwards of 100 amps when first turning the motor. dont believe me throw an amp clamp on the battery positive while cranking. that takes alot of power. what the cluster showes while cranking is not a good indication of anything cause most of the power available is being used by the battery. but like said if you verified its the same on another car. what is the problem. does your car not start?

[90turbo1]

and yes to answer your question a low battery that does not come back after a serious load can... cause missfiring and all other sorts of things to malfunction.

[Honolulu]

Know that it's amps that start the car, so really, it's not a low voltage reading you're concerned with, but it is an indicator of low amps and that's a concern. I won't get into the relationship, but E=IR known as Ohm's Law is behind it all. Not knowing the resistance, we can't complete the equation.

The real answer is to get your battery load tested, it's usually free. But in your situation I'd probably just suck it up and replace the battery.

[MIKYZZ4]

Have a diagnostic scan done.
Let the computers reveal the error codes,
then we can narrow down the possible causes of the misfiring.

[tomsh96]

First of all thank you guys for your time and answers I'm not into this whole electronic stuff, so please forgive me. The reason why I asked this because I try to find the source of the startup misfire that disappears after ~30 sec and I keep thinking about this. I'm taking the car to a specialist tomorrow, hopefully he will resolve this, and I can write the solution here.

[Eaglesail]

Upon key turn...momentary is a drop of dc voltage count, the power behind is its deliverance measure is in amps. Amps are a collection of electrons stored within a lead cored battery (usually) there are other mediums. Due to the natural degradation of galvanic entities, all batteries begin to die the day they were born. Better battery construction ( Rolls-Surrette) battery supplier to locomotive and ships can live 12 to 15 years..depending usage. Battery life is generally measured in cycles...ie discharge-recharge and the depth of their discharge. Car batteries typically live 5 years on average. The older the battery, the higher is the resistance to charge. This means that your alternator will work harder...thus requiring more maintenance...and replacing an alternator in an e46 is quite costly!