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Old 3rd July 2009, 23:12   #1
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Default Idling fluctuations!! only when headlights on

i had upgraded the headlights on my alto to philips rally vision 100/90 bulbs.
since then i am facing a idle surge when i put my headlights on. i have installed a PMP relay too.

now its quite sure that the engine is getting starved of electrical power somewhere. i have already changed the IAC valve suspecting it was the culprit. now its very much clear that the idling surge is there only with headlights on. it disappears as soon as i switch off the headlights.

whats exactly happening here? isnt the alternator giving enough current or is it the coil/distributor not able to cope up with the additional power being withdrawn.

can someone throw a light on this. i suspect its the alternator.
can anyone please suggest any way to calibrate alternator or anything related to electrical supplies here.
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Old 3rd July 2009, 23:22   #2
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The same way the rpm increases when you turn on the AC.

The alternator charges the battery and powers up the full electrical system when engine is running.

If a particular part of the car is drawing more current the alternator has to turn that much faster to power that part. Since the alternator is connected to the engine using the alternator belt the ECU senses this and increases the rpm.

It's pretty normal. I can hear the rpm go up in my car as well when i turn on the lights. I'm not even running high wattage lamps, just stock 55/60W.
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Old 3rd July 2009, 23:37   #3
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ya but in my case the RPM is dropping not increasing.
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Old 3rd July 2009, 23:50   #4
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Originally Posted by amit_mechengg View Post
ya but in my case the RPM is dropping not increasing.
Then why is your thread title idle surge??
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Old 4th July 2009, 00:03   #5
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We are facing a similar issue with Baleno. Whenever we switch on AC at idle, initially for a couple of seconds, the rpm will go up and then its a bit below normal.
Similar activity takes place when we switch on AC when the car is idling. Infact I think that blower unit will need power, so the altnernator has to turn faster and add to that the load of compressor, so the rpm must increase.
Our headlights are 55/60W but still the rpm will go up for a couple of seconds and then come below normal.

As far as AC goes, I think there is something called " AC idle control ", though I am not sure whether its there in MPFi cars or not, but in case of carb models something like that was available such that if the ac is turned on, the rpm will go up.
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Old 4th July 2009, 00:40   #6
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I have kind of same problem in my car. But not with headlights.

I have front power windows in my car. If i roll up 1 power window at a time everything is fine but if i roll both up at the same time engine looses power.

Though i am thinking of BIG 3 upgrade since that might help.
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Old 4th July 2009, 09:27   #7
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There is nothing wrong, really, except that the idle speed control is not compensating for the load increase. When load increases, engine RPM dips, ECU is supposed to adjust injection control ever so slightly (if there is load compensation) to maintain idle speed. The effect is more noticeable in smaller capacity engines.
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Old 4th July 2009, 09:36   #8
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hey there is no ac ideling control,or ecu sensing that more current is being drawn by headlights,its just that,both AC generator as well as ac comperssor are in direct couple with engine,when they are switched on,engine is loaded,sensing engine load more fuel is injected to copeup,hence rpm rise,however ecu constantly updates itself and keeps trying to reduce rmp upto the idle threshhold because of no throttle input,in some cases(cars) the engine produces enough torque at idle with just a slightly richer mixture,in this senerio the rpm falls back with slightly richer mixture,others the rpm rises slightly to produce just enough torque to keep revving.

even in crab modles below certain rpm,the solonoid valve in the crab operates to uncover another jet to add fuel,so when ac is switched on,rpm tends to fall,taking it below the set limit and hence additional fuel goes in,so rpm rise again! however in crab models ,it usually means that crab butterfly is not in good state and is leaking air into engine even with no throttle,because solonoid is suppose to be open at idle anyway!.but when buterfly is already leaking air,or crab is in bad state of tune,enough charge is already fed to engine not requiring the solonoid valve to operate(consumes more fuel in this condition)
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Old 4th July 2009, 10:28   #9
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Quote:
Originally Posted by vid6639 View Post
Then why is your thread title idle surge??
what i meant was fluctuations. sorry to call it surge

Quote:
Originally Posted by abhibh View Post
I have kind of same problem in my car. But not with headlights.

I have front power windows in my car. If i roll up 1 power window at a time everything is fine but if i roll both up at the same time engine looses power.

Though i am thinking of BIG 3 upgrade since that might help.
same problem i found on one more alto. when the power window in operated the idling RPM suddenly drops and there are vibrations in the engine.

i am just trying to figure it out whats exactly causing this. is it the alternator that cannot cope-up with the extra electrical load or is it the ignition coil dropping the extra voltage to the spark plugs?
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Old 4th July 2009, 11:17   #10
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are mere bhai bataya to,it isnt that alternator is not producing enough current,just that at ideling there is not good enough torque left to meet the sudden increase in electrical load .isnt that simple enough...now either the revs will rise,or ecu commands for richer mixture.

and what has this to do with ignition coil(i mean what da heck is going on here),ignition coil has a very simple job to do,it draws very minimal current(in milli amps) increase its voltage to a high lever(of the order of 32-44k volts),spark plugs require high voltage not high current,now why would the coil drop extra voltage(i dont understand wht on earth the term "dropping the voltage to spark plug" act means) spark plug gap is design spec of plug,and the coil is calibrated to provide enough volts to the plug ,so that it can jump the gap between terminals of plug and cause a spark,is gap is constant,there is absolutely no requirement of extra voltage,because whole idea is just to produce the spark good enough for ignition,anything more than that will be waste(as noone will be standing inside the combustion chamber to enjoy the flashing brillance) and anything less will simply wont work as it wont be jumping the gap. so i dont know where did u get this idea of dropping extra (holy heck)volts to spark plug.

vibration in the engine is always observed when it is operated under heavy or over load condition(less then required torque available),either be it driving in top gear at low speeds,climbing hill in higher gear at low rpm,or be it electrical load at ideling...Same Answer just not enough torque!!!
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Old 4th July 2009, 12:14   #11
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Quote:
Originally Posted by amit_mechengg View Post
i am just trying to figure it out whats exactly causing this. is it the alternator that cannot cope-up with the extra electrical load or is it the ignition coil dropping the extra voltage to the spark plugs?
Its quite possible that the alternator cannot cope. Why don't you get it connected to a scanner and then check the voltage delivered by the alternator when the lights are switched on?

Also, it would help if you changed your stock plugs to something better as that would help deliver a better spark and hence stop the fluctuations.
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Old 4th July 2009, 12:41   #12
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Its quite possible that the alternator cannot cope. Why don't you get it connected to a scanner and then check the voltage delivered by the alternator when the lights are switched on?

Also, it would help if you changed your stock plugs to something better as that would help deliver a better spark and hence stop the fluctuations.

and something better in spark plugs whould be..???

also in the event when alternator isnt able to deliver enough current,there is a thing in the circuit called a battery,current is drawn from it incase demand is more than supply.
that is why people end up with drained and dead battery when they put on too many lights and horns on smaller engines with smaller alternators.

however i am not dening that tere is a problem in your case,
there may be two of them.
1.your vehicle has been driven very softly,mildly with bare minimal acceleration,as ecu is adaptive to habbits of driving,it has recorded too lean values for ideling rpm,hence whnever there is slight load(electrical or otherwise),it becomes an overload.

easy way to find out if this is the problem. After you have driven for about 15-20 mins or more(just to make sure the engine has warmed up,ecu settings are no longer at cold start),(drive very mildly for this experiment)
shut down the engine!
start again,slot it in 1st,and see if the car picks up and keeps moving without any throttle.be sure to switch off all electricals during this.
look out for jerks,shrudders,or fluctuating revs during this.

ideally car should move and settle on a constant pace.
if it does then good,else get the idle adjusted(yes in mpfi too u can get it adjusted).also you can reset the ECU to factory settings

2,check spark plug gap,it might be possible that one of the cylinder has a plug with too much or too little gap,with on cylinder not firing atall,torque would obviously be too low.no reason to switch to so called better plugs,unless you have performance tuned your car and are running higher comp ratio,or a turbo or something which has increased your horsepower above normal spec.
spark plugs recomended by the manufacturer are good enough,thats why they have been recomended in the first place.

Last edited by dustom_99 : 4th July 2009 at 12:44. Reason: addintion of comment
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Old 4th July 2009, 13:18   #13
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There is a mechanical device in some cars like indica, which increases engine rpm slightly when the electrical load increases.
The indica has these.
I suspect your alto's that device is faulty.
Your cars rpm should slightly increase and then settle at slightly higher level.
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Old 4th July 2009, 15:45   #14
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Originally Posted by tsk1979 View Post
There is a mechanical device in some cars like indica, which increases engine rpm slightly when the electrical load increases.
The indica has these.
I suspect your alto's that device is faulty.
Your cars rpm should slightly increase and then settle at slightly higher level.
That device is the idle air control valve. It adjusts idle depending on load on engine.

I think he already got that replaced. It's a small valve below the throttle body.
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Old 4th July 2009, 16:05   #15
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Quote:
Originally Posted by dustom_99 View Post
are mere bhai bataya to,it isnt that alternator is not producing enough current,just that at ideling there is not good enough torque left to meet the sudden increase in electrical load .isnt that simple enough...now either the revs will rise,or ecu commands for richer mixture.

and what has this to do with ignition coil(i mean what da heck is going on here),ignition coil has a very simple job to do,it draws very minimal current(in milli amps) increase its voltage to a high lever(of the order of 32-44k volts),spark plugs require high voltage not high current,now why would the coil drop extra voltage(i dont understand wht on earth the term "dropping the voltage to spark plug" act means) spark plug gap is design spec of plug,and the coil is calibrated to provide enough volts to the plug ,so that it can jump the gap between terminals of plug and cause a spark,is gap is constant,there is absolutely no requirement of extra voltage,because whole idea is just to produce the spark good enough for ignition,anything more than that will be waste(as noone will be standing inside the combustion chamber to enjoy the flashing brillance) and anything less will simply wont work as it wont be jumping the gap. so i dont know where did u get this idea of dropping extra (holy heck)volts to spark plug.

vibration in the engine is always observed when it is operated under heavy or over load condition(less then required torque available),either be it driving in top gear at low speeds,climbing hill in higher gear at low rpm,or be it electrical load at ideling...Same Answer just not enough torque!!!
my bad. what i wanted to say by drop in that extra voltage is that the extra electrical load due to headlights is causing the drop in voltage across the spark plugs. earlier this was more pronounced. but this has reduced a bit when i switched over to NGK G power platinum tip plugs.

to back up to this i am hearing mild explosions through the exhaust. this happens when unburnt fuel goes from the cylinders to the exhaust. this happens only when the headlights are on. during the day time i never hear these explosions.

due to this i am suspecting that there is not enough spark in the combustion chamber or the spark duration is getting altered when the extra electrical loads pop in.

well i will hook in the Tech 2 and check it in my next servicing.
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