Mysteriously poor running engine after jump starting

So I guess it's the season for stressed batteries (been seeing a few threads here lately). I'm having a strange problem with how my car runs sometimes immediately after a jumpstart.

I'm been making some audio-related tweaks to the car, and the process sometimes drains the battery (lights on, amp on, radio on etc while car is off) while I've been working. That's pretty much just my doing. It might not be the greatest for the battery, but the battery is cheap and on the older side, so I'm planning on replacing it with a better one soon anyways.

My issue is when I jumpstart the car, I sometimes have issues. I use a 300A jump box connected to the terminals under the hood, and pretty much only use it fully charged. I've used this jumper for a while and it's never given me any issues, usually jump starting the car easily.

Here's what's been happening: when I crank the engine, it turns over somewhat reluctantly, but still definitely fast enough to start it. It might take 5 seconds or so of cranking, which is unusual. Okay. But when it does finally start, the engine runs EXTREMELY poorly, like it has multiple misfires. The traction light also comes on, and all the electronics dim horribly with the engine as it labors tremendously to turn over. Removing the jumpbox at this point makes it even worse.

I always turn it off almost immediately, recharge the jumpbox and try to start it again later. It might repeat the same behavior, or the engine will instead turn over easily, and it will start and run fine, with no warning lights.

My first inclination would be the alternator. But the alternator is an new Bosch installed only a few months back and it seems to have no problems. I've already replaced the grounding straps too. Again the battery isn't terribly new, but my mechanic maintains that it will have no bearing on how the car runs once it's started.

Any ideas? EDIT: I remember someone else mentioning something like this happening, but can't find the thread.

Did you look for codes after the issue showed ? Sadly, I don't have other ideas.

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Originally Posted by fredo

Did you look for codes after the issue showed ? Sadly, I don't have other ideas.

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Guess I could've checked when I went to the Advance earlier but forgot. I'm going to assume it was electrical related. Bought the biggest battery they had that would fit, which was a Duralast AGM H8 900 CCA. High internal resistance draining the current away from the rest of the car on a cold start? Who knows. At any rate, battery was indeed shot, and my starter has never sounded happier.

E46s do weird things on weak batteries, including poor running. I don't know of any other car that's like that. So in theory, your mechanic is right. But not with these cars.

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These are classic symptoms of low voltage. When the engine is reluctant to start there is most likely a large voltage drop from a poor jump box connection. This causes control modules to act up, sometimes a misfire occurs and the DME turns the cylinder off until there is a key cycle.

I personally would not worry about it while you are discharging the battery like you are. Finish your wiring, replace the battery and clear the entire vehicles fault memory. If it still continues to happen start diagnosing at that point.

Thanks all for the replies!

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Originally Posted by GeorgeH

These are classic symptoms of low voltage. When the engine is reluctant to start there is most likely a large voltage drop from a poor jump box connection. This causes control modules to act up, sometimes a misfire occurs and the DME turns the cylinder off until there is a key cycle.

I personally would not worry about it while you are discharging the battery like you are. Finish your wiring, replace the battery and clear the entire vehicles fault memory. If it still continues to happen start diagnosing at that point.

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Agreed, I think that must be it. It seems strange that once the car was started and the alternator is spinning, there could still be a voltage starvation. I know that the battery likely had a high internal resistance due to age, which would greatly diminish the ability to drive the electrical load of starting it, but once it was started, I'm not too sure about how that would play out.

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Originally Posted by usinjin

Thanks all for the replies!



Agreed, I think that must be it. It seems strange that once the car was started and the alternator is spinning, there could still be a voltage starvation. I know that the battery likely had a high internal resistance due to age, which would greatly diminish the ability to drive the electrical load of starting it, but once it was started, I'm not too sure about how that would play out.

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There likely isn't but that modules have already seen the low voltage and put themselves into a "failsafe" state. They wouldn't return to normal operation until a key cycle.