Idle rpm will drop when put electrical load no meter what, low beam, cabin fan... And light is dim on that moment, intesting situation is when turn on low beam, cabin fan to 4 and climate is on no more rpm drop in any situation.
General Stilo 1.4 rpm drop on idle with electrical load
- Thread starter Nikola357
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General Stilo 1.4 rpm drop on idle with electrical load
Mike1alike
Established member
That says the culprit is as I've mentioned, the alternator. Or, I think that it is.
Although you may find that interesting, it kind of makes sense. When you turn the climate control on, the RPM is higher than when it is off, about 100 RPM more. It's like if you'd gently pinch the accelerator pedal. That compensates and makes it not to feel that voltage drop you feel when engine runs on idle RPM, climate off.
And actually, before you get to the alternator itself... how old is it's belt? And are all the pulleys and tightening roller move free? I don't think the problem is with them, but make sure it isn't. It could have been with belt if it happened when you increase the engine load, but it happens when you increase the electrical load. So it's either the alternator, either the battery. What state is the battery in, I don't know if you've mentioned something about it? How old is it, how charged/discharged? Can it be dying, like having a shortcut between two elements inside?
Although you may find that interesting, it kind of makes sense. When you turn the climate control on, the RPM is higher than when it is off, about 100 RPM more. It's like if you'd gently pinch the accelerator pedal. That compensates and makes it not to feel that voltage drop you feel when engine runs on idle RPM, climate off.
And actually, before you get to the alternator itself... how old is it's belt? And are all the pulleys and tightening roller move free? I don't think the problem is with them, but make sure it isn't. It could have been with belt if it happened when you increase the engine load, but it happens when you increase the electrical load. So it's either the alternator, either the battery. What state is the battery in, I don't know if you've mentioned something about it? How old is it, how charged/discharged? Can it be dying, like having a shortcut between two elements inside?
Belt is about 3 years old and 20000km, pulleys is ok I guess, everything rottate normally, battery is four years old but same thing is hepen when it was new, I suspect on bad diode panel on alternator, i check this days with multimeter charging battery and alternator So I'll report back with the results. Thanks for help
Mike1alike
Established member
Forgot to mention the cables and I see they've not been mentioned. So you can check them, as well. First thing, the ground cable, you know the drill or you can find about it, how to check, how to replace it if needed. That's the (-) V from battery to body and further to gearbox. And the (+) V cable, as well. Clean both cables' terminals connected to the battery. And there is one big (+) V cable going from the battery to the fuse box. Get to that end and clean that connection there, too. And there's the other big one going from battery to the alternator, having a 'pit stop' at the starter motor. Clean them contacts as well and also clean the other (+) V cable contact from the starter motor. Of course, before doing anything at it, remember to disconnect the (-) V cable from battery so that you can work free and don't cause any damage.
With the alternator, to check the diodes do a AC voltage reading (on the battery terminals is fine) while the engine is running, using a good multimeters (the simple cheap multimeter can't do proper AC reading on DC circuit and throw bad values). AC voltage that comes out of the alternator should be under 50 mili Volts. If it's more than that, one or more diodes are toasted.
Mind you, with the alternator, besides the diode panel and the voltage regulator, there's also the core of it, the stator and rotor assembly that can get worn out or suffer damage. The alternator is an auto part that cannot last forever, that's for sure. You've mentioned 13.4 V output and that tells me your alternator is on its way out. Replacing it with a new one is the best you can do, and the cheapest on the long run. I strongly recommend Denso with the specs your car needs.
With the alternator, to check the diodes do a AC voltage reading (on the battery terminals is fine) while the engine is running, using a good multimeters (the simple cheap multimeter can't do proper AC reading on DC circuit and throw bad values). AC voltage that comes out of the alternator should be under 50 mili Volts. If it's more than that, one or more diodes are toasted.
Mind you, with the alternator, besides the diode panel and the voltage regulator, there's also the core of it, the stator and rotor assembly that can get worn out or suffer damage. The alternator is an auto part that cannot last forever, that's for sure. You've mentioned 13.4 V output and that tells me your alternator is on its way out. Replacing it with a new one is the best you can do, and the cheapest on the long run. I strongly recommend Denso with the specs your car needs.
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Sparkplugs picture indicates, that engine burns some oil. Not much, but may be enough to weaken the idle, due to blow-by (stuck piston rings).
Check the exhaust emissions. The HC and CO content in healthy engine is zero (if not, there is a problem). And not much O2 left (if it's like 0,5% or more, there is an exhaust leak for example, spoiling the lambda sensors). Also, the intake vacuum tells the condition of the engine (but you must know the proper value for that engine, for example in 1,4 8V and 16V - Grande Punto - it should be 290-330 mbar, official data).
But, the alternator behavior is not OK. Too much voltage drop (even when the engine has weak idle it should be closer to 14 V).
When AC is On, the behavior is OK, because with not enough refrigerant, ECU will rise the RPMs = engine is not in idle mode anymore (it's stronger).
Check the exhaust emissions. The HC and CO content in healthy engine is zero (if not, there is a problem). And not much O2 left (if it's like 0,5% or more, there is an exhaust leak for example, spoiling the lambda sensors). Also, the intake vacuum tells the condition of the engine (but you must know the proper value for that engine, for example in 1,4 8V and 16V - Grande Punto - it should be 290-330 mbar, official data).
But, the alternator behavior is not OK. Too much voltage drop (even when the engine has weak idle it should be closer to 14 V).
When AC is On, the behavior is OK, because with not enough refrigerant, ECU will rise the RPMs = engine is not in idle mode anymore (it's stronger).
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Yes oil consumption is about 300ml per 1000km but I have mostly sity drive, my car passed MOT this year and I ask what about emissions but everything is OK, absolute intake pressure on idle is 300mbar. Something is wrong with my electrical sistem, battery, alternator, wiring, thank you for helping.
