turning lights on makes idle drop and become unstable?!

[kwazza11]

well my RB20det has developed an interesting problem...

whenever i turn the lights on the idle drops and the engine shudders and shakes like its misfiring! not a real bad misfire like when you isolate a cylinder but noticable nontheless.

what the hell could cause this? anyone had this happen? i've just replaced the battery so it cant be running out of charge surely?

its been using more fuel than usual lately too if that counts.

Karlos

[Al]

The alternator may be on it's way out. It may be able to slowly charge the battery (with no lights on), but once you increase the load/drain it will not be able to cope.

[skyline33]

was just about to say the alternator, agreed with Al

[WazR32GTSt]

ditto above. you will find it probably happens with the windows and fan etc as well.

did u just have a dead battery? definately the alernator that's why the battery died too...

re: using more fuel

unrelated. drive more conservitavely...

[kwazza11]

well charge gauge says i'm charging at 14.5 volts but i'll double check with a multimeter tomorrow.

dont think it was the altenator that screwed the battery as it just died after i didnt use the car for a few days, after that the battery wouldnt hold charge (was about 3 years old too).

actually i've relaxed on the throttle lately so it shouldnt go up like it has.. mabye i should drive faster to save on fuel

[Guest RedLineGTR]

youve probably been fanging it more thats why your fuel is up.

[Al]

Charge is not properly measured by volts, its the current that's important. The charge relay that's attached to your alternator could also be faulty. If the voltage drops a fair bit when you turn your light on, it's because there isn't enough current.

[SKYLINED]

Need to test the battery under load, then u can see if your battery is holding enough voltage.

Need a tester though.......

[kwazza11]

ok just got the multimeter out and checked the voltage. at idle charge is 13.9 and when lights are turned on and idle drops etc the voltage drops to 13.8 not much of a difference yet it affects the cars running by a long shot.

also noticed the voltage doesnt raise with the revs. stays at a fairly constant 13.9

[wrxhoon]

when lights are on cause the alt is loading up the revs drop as simple as that . normaly u r computer will pick it up and increase the revs to compansate just like when u put the air cond on so u may have some prob with the idle speed .