Battery discharging and engine misfire.

[RS2Ken]

Hi all, 

Well after over 5 years of trouble free motoring my S2 Elise Sportsracer seems to have developed a fault. Initially I have noticed that if the car is not used for greater than 3 days the battery goes flat requiring recharging. 

I trickle charged it overnight last night and used the car this morning without issue as she started first time. My commute to work is only a couple of mile, but on arrival I thought I could smell something like a hot electrical component as if it were burning.

I checked all I could but could find no issues.

At the end of my working day, I again started the car with no issues. I left the car on tickover for a few minutes while talking to one of the cars admirers at work :-)

Once ready to set off, the car stalled and took a while to restart. On trying to drive off again the car developed a small misfire but kept running but always felt like it was going to stall again. I managed to get home and again had a look in and around the engine for anything obvious but could find nothing wrong.

The only test I have carried out so far is to check that the battery is receiving a charge while the engine is running which it is.

Has anyone had a similar fault or can anyone point me in the right direction to get the car running sweet again please.

Any help or advise is gratefully received.

[timbo]

I'd start by checking the following:

1) Battery voltage disconnected

2) Battery voltage connected (ign. off) - there should be a small drop from above, but not massive

3) Leave the battery disconnected for a few days and see if there is any voltage drop

It could simply be the battery's failing and so the alternator is having to overwork to compensate.

If you have access to a good multimeter or ammeter, you could also check the current drain from the battery but only with the ignition off.

[RS2Ken]

Thanks Timbo.... could the hot electrical smell be the Alternator then..? also would it cause the car to stall and misfire afterwards..?

I'll try what you suggest. Hopefully it is just the battery on its way out... its just in its warranty too so could be a timely fault.

Thanks for your help.

[timbo]

The fact that the battery needs recharging after 3 days non-use suggests its either not holding charge or losing it somewhere. 5 years life isn't unreasonable so it could well just be the battery's on its way out.

Check the voltages as mentioned - you should be seeing 12-13v disconnected and not much lower with it connected and nothing switched on. With the battery freshly charged then left disconnected for 2-3 days, it shouldn't really drop if it's okay.

[RS2Ken]

Thanks again Timbo.

[duncx]

Certainly could be a dead cell in the battery. Modern cars are very sensitive to voltage so you can find that the starter still sounds reasonably healthy but the electronics are struggling. Checking the voltage with a multimeter might show the problem - a check on a healthy battery with everything switched off should give you around 12.6v, if you then switch on the ignition and lights (don't start the engine) it will drop a little but should still maintain above 12v. If it drops below 12v then suspect a dead/dying cell. With the engine running and a healthy alternator you should see about 13.5 volts at the battery.

If it's not the battery the rectifier on the alternator could have died - this could be the reason for the battery discharging as rectifiers can 'leak', even without the ignition switched on. 

Good luck 👍

 

[RS2Ken]

Thanks again for the help. I'll carry out the checks over the weekend. I started and drove the car to work today without issue. A friend from a nearby garage plugged into the car to read for any faults and none were registered. Quite happy about that but it also leaves a little bit of uncertainty as to wether the fault will re occur.

Took the car for a good run after work and all was ok... no issues at any revs.. pulled like a train.... I'm hoping that's it.... but I hate intermittent faults.