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Discussion Starter #1
Hello All,

Like many of you, my S240 Exige sputters and runs like absolutely crap for the first minute or two after starting from cold when the car has been sitting for a few days. My symptoms would be a very rough running engine (super rich AFR) with a lower than normal idle at first start ... and then it smoothes it self out. This is after the car has been sitting for more than 3 days without being run. Each subsequent start afterward would be fine if you started it up to 2-3 days later. The longer the car has sat without being started, the worse the engine would run on first start.

Anyways ... I was determined to find the cause and I think I finally found it! On a hunch, I checked the voltage on my battery as I ran into similar starting issues with my jet boat of all things. It read 12.2V which I figured was ok ... but when I put the key in the ignition position (which lights up all the electrical components) the voltage dropped down to 11.4V ... Not Good! So I hooked up the trickle charger for about 4 hours and waited for it to complete a charge cycle. I double checked the voltage and it was 13.2V without the key in and 12.4V with the key in the ignition position. Then I started up the car which had been sitting for over a week without being and started and BANG ... started and ran super strong. So my conclusion is that the alarm drains the voltage down enough when you leave the car sitting that on first start ... it takes a few seconds for the alternator to kick in and supply the extra voltage to get things running properly.

Not sure if this is the solution to everyone's problem ... but at least it's a good place to start if you have rough starting issues! I guess the solution is to just drive the car more :)

Cheers,
Zoomby_U
 

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I'm not an expert, but I don't think this is the cause...
Once the engine starts, a weak battery would not cause a rough running engine. The battery's role is to start it...
just my 2 cents.
 

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Discussion Starter #3
I think it may be possible that the ignition system is not getting enough voltage and thus causing misfires or an incomplete spark. I've definitely seen spark plug issues causing the engine to run rough ... so it may not be as far fetched as you might think. All I know is with the battery under 12V it starts rough and with it above 12V it's a totally different story :) Hopefully some others can weigh in!

Cheers,
Zoomby_U
 

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Zoomby, you are dead on with your theory. I've seen it many times before, the ecu doesn't have sufficient voltage to operate all sensors properly. If the battery is low enough it will draw enough current from the alternator initially to cause a poor running condition. I would imagine if the alternator was larger there would not be as much of an issue, but that is what is happening.
 

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Discussion Starter #6
Thanks for the reply mikelr ... I started the car today after having it sit for two weeks and it started ... but a little weaker than when the battery was fully charged ... ie. it didn't rev up as it usually does to about 3-4K. I'm pretty convinced that it's a battery voltage issue ... I think I might have to spring for a Chimera to fix the problem :)

Cheers,
Zoomby_U

Zoomby, you are dead on with your theory. I've seen it many times before, the ecu doesn't have sufficient voltage to operate all sensors properly. If the battery is low enough it will draw enough current from the alternator initially to cause a poor running condition. I would imagine if the alternator was larger there would not be as much of an issue, but that is what is happening.
 
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