Engine runs rough when lights turn on

[bav]

Having a problem with my 1972 240 Z. When I turn on the headlights the engine seems to idle worse, turn off the lights and it smooths right out. Anybody know what might be causing this?

Brian

[Gav240z]

Well it could be that your switching the lights on is causing more "load" on the alternator which makes the engine rpm's drop. It's quite normal in most cases you could try increasing the idle speed if it's really low but in most cases I wouldn't worry.

You haven't been really descriptive, if your battery is very low as a result then you should probably check the water levels and retop with distilled water if neccessary.

I really need a better description of what you mean by "rough" does it start to backfire or hesitate or just idle lower and cause the car to shake a little more?

:nervous:

[bav]

Gavin

Thanks for the response, The car idles around 1000 RPM and there is really no noticable drop in the idle when I turn on the lights but the engine starts to run rough like it might be missing now and again and it will really hesitate when I press the accelerator. I'll check battery voltage first but if not that then what?

[Gav240z]

Ok well first I would want to confirm that the problem is electrical. Since I had this problem with my "260z" when I had a thermo fan attached which would drain even more power from the car.

The good thing about a 260z is you can see the voltage meter in a 240z it's a bit harder with amps. Is there anyway you can hook up a volt meter while your in the car to see this? Your volts should sit between 12 & 16 ideally at around 14 anything lower than 12 and you know it's a charge problem. As I said before you should confirm this is a problem with the electrical system and nothing else.

If you are sure check the battery water levels as you may or may not know each cap in the battery has it's own reservoir(spelling?). If they are above the electrodes either your battery is stuff or it's a charge issue.

The next place to look is the alternator, if you look on the back of the alternator you can tell if it's fried by the metal connector at the back it will look burnt out 9/10 times that's what stuffs up and causes huge resistance sometimes it can be internal or the voltage regulator but check these other items first.

Since you do say it's when the headlights are on I'm inclined to believe it is electrical however with these problems I stress you don't disregard any other area.

[bav]

Thanks for the help. I put a voltmeter on yesterday and it appears the battery has had it, showing 10-11 volts with the engine off and barely 12 with the engine running with the lights on. (Shows 14V and change with no load while the engine is running) I'll swap out the battery this weekend and see if that takes care of it

Thanks again

Brian

[Gav240z]

Yeah sounds like a charge issue see how the battery goes. If not look toward the alternator.