Bad Alternator?

A

alfie15

I have a strange issue with my little car, in the last few days when I put the headlights on at night the car feels like it's going to stall and looking at the rev counter the revs dip significantly and then begin to rise. Along with this the alternator sounds like it's whining, so this morning I thought I'd check the stereo to see if everything was connected correctly and while I was at that I changed one of the blown bulbs in the instrument cluster.

To cut a long story short I figured I'd start the car with the instrument cluster disconnected and the car was idling superbly and even putting the headlights on the alternator didn't whine, so I tried connecting a spare instrument cluster and I was back to a whining alternator. In my mind I thought I'd leave that connected and unplug the alternator while the car was running and lo and behold the idling returned to normal.

My question therefore is do I have a knackered alternator or am I barking up the wrong tree? Any and all input is welcome. Thanks
 
That's good to know thanks frank. I'm seriously baffled with the car though cos when I disconnected the alternator itself the idle improved and likewise if the alternator is plugged in and the dash removed the idle improves. With the alternator and the dash plugged in my diagnostic computer says the revs are at 680rpm, disconnect the dash and it's at 760 rpm. Putting the headlights on with everything connected up and the revs drop to 560rpm and stay there a few seconds until they increase to 640rpm. The whine from the alternator under load has only happened in the last week.

Could the alternator be failing or am I looking at a bad earth, shorted wire?
 
I've had the throttle body off and cleaned and the idle control replaced from a donor car that was working 100%. Any ideas why disconnecting the alternator improves the idle? It's leading me to suspect a failing alternator but it's always good to get a 2nd opinion.
 
its just that the alternator draws power from the engine alfie, so if the idle control valve is,nt increasing the throttle to suit, then the idle rpm will drop
 
With the engine idling and nothing else turned on, try pressing the rear demist button. If the revs rise, then the ICV should be ok, if not, then suspect the ICV.

I've got one of these permanently plugged into the dashboard DC socket:

Dashboard Voltmeter 12v

It's really useful for giving me real-time information on what voltage my alternator is putting out whilst running and under different loads.
 
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I understand your reasoning frank, I must add that I changed the idle control today but it didn't make a blind bit of difference to the idle. It does seem that it's doing its job by increasing the revs when the sidelights and headlights are on, it seem to take a few seconds for the idle to increase and the idle settles back down when they are turned off.

What has me confused is the idle is perfect when the alternator is unplugged.
 
I tried your suggestion alfantasti and with nothing else turned on I switched on the rear demist and the idle does indeed increase.
 
your idle control valve is a stepper motor eh alfie, i assume it works like the earlier i/c/v ? (a controlled air leak into the inlet mani ) it may need re-syncing/reprogramming ?
 
alfie15 said:
I didnt realise they could be reprogrammed/resynched. Do you happen to know how that's achieved frank?
Click to expand...
fraid not mate, the prefacelift ecu has various inputs from the power steering valve/heated rear screen/heater motor etc too, so that the i/c/v could compensate for the extra loads
 
IACV rarely need reconfiguring. in most case they just need an annual flush clean.

if you have a pre-face TB like this pic,

k550i-466-jpg.29307


the IACV motor could be synced with the valve head using a diagnostic software like this:
https://www.micra.org.uk/threads/pollymobiles-rebuild.35251/page-19#post-446256

if you have a later face-lift bosch TB with the IACV at the back, they're sealed and can't be configured.

the fact that the IACV automatically idles up when you turn on electrical loads that the ECU is monitoring (ie headlights, demister, heater fan) means the IACV is working ok.

when you unplug the alternator from the loom and it runs fine purely from the 12v battery, means the alternator was applying some extra electromechanical load to the engine but the ECU hasn't idled up the IACV to compensate cos it's unaware of any additional load.

also it ran better with the dash disconnected sounds like an issue related to the dash/lighting circuit.

sounds like there's an extra excessively heavy electrical load or a short induced into the circuit.
 
Thanks polly, the alternator whines terribly at idle and when any load is put on it from the lights, heater or rear demist. The idle drops then slowly goes up when any load is put on the car, disconnecting the alternator fixes that problem. I'm suspecting that the alternator is failing anyway but your thought about a short makes sense.

I thought I'd check the fuses inside the car this morning and removed the fuse marked meter and the car runs fine, removing that fuse leaves power to the dash milage display but removes power from the rev counter, fuel and temperature needles.
 
grinding noise could be bad alternator bearing. if it stops whining/grinding when u run engine without the alternator belt, could be that bearing.

while the belts off, spin the alternator by hand and spot any bearing play or hear obvious rough damaged bearing noise.

the alternators rotor bushes at the rear also have a finite lifespan. when they get worn down, it stops working which sometimes trigger the battery light and stops charging the battery, eventually the battery runs flat and whole car stops.
 
The whining noise is only happening when the alternator is under load. As I say when I take the fuse out for the instrument cluster the rev counter, fuel and temperature gauges stop working but the idle goes back to how it should. Fuse in and the idle is lumpy. I'm really baffled with this now.
 
I've also also noted that if I put the headlights on remove the instrument cluster fuse and open the door the beeper goes off. Fuse in door open, lights on and the beeper only works if the engine is off
 
check there's no shorting in the instruments ie when you changed bulbs, are any contacts cross-shorting.
try removing all the bulbs off the cluster, check if its fixed. yes = shorting bulb, no = related to instrument wiring but not the bulbs.
if it runs fine with no bulbs, begin reinstalling each bulb by bulb till the fault returns and it maybe that bulb.
 
alfie15 said:
I've also also noted that if I put the headlights on remove the instrument cluster fuse and open the door the beeper goes off. Fuse in door open, lights on and the beeper only works if the engine is off
Click to expand...

beeping when lights on, IGN off & door open is normal, to remind driver they left lights on while stepping out.
 
If I take the instrument panel fuse out. Fuse 8 I believe and have the engine on, lights on and open the door the beeper works. But if I replace the fuse and open the door with lights and engine on it doesn't beep, only when I switch the engine off. Is that normal?
 
alfie15 said:
The whining noise is only happening when the alternator is under load. As I say when I take the fuse out for the instrument cluster the rev counter, fuel and temperature gauges stop working but the idle goes back to how it should. Fuse in and the idle is lumpy. I'm really baffled with this now.
Click to expand...
the alternator uses the 5w telltale dash light as a current draw for the field coils in the alternator to kick in alfie, so removing the dash plug or fuse will cause the alternator to spin freely (not charge)
 
Thanks for all of your input guys it's much appreciated. Is the fact that the idle improves when the alternator is just free spinning or even when it's disconnected altogether a sign the alternator has had it or is it more likely a wiring problem? I've checked all of the bulbs as polly suggested but things were just the same.
 
the fact that the idle is ok when its spinning but not charging does,nt point to bearing friction, so sounds like an idle control valve issue to me
have you measured the voltage when running/charging alfie ?
 
The idle control seems to work, the idle goes up when headlights etc are turned on. Disconnecting the idle control results in the car revving up and down until it's plugged back in. The idle control has been off and cleaned and also replaced with a known working one and the car still idles badly, both idle control valves behave the same way or rather the car behaves the same regardless of which valve i use.

I don't have a multimeter to hand to check the voltages of the alternator.
 
yes but the i/c/v is relying on the sensor inputs and ecu, so if the 2 i/c/v,s were,nt getting the signal to open the rpm will fall
i only asked about the voltage to rule out a possible alternator voltage control problem
 
That makes sense to me, but using the rear demister the idle increases so I'm assuming that is the idle control that's doing that or am I missing your point ?
 
you said that the car nearly stalls when you put the lights mate ?
an obd2 diagnostic setup will give you i/c/v position % open/closed, they,re very cheap nowadays eh
 
I did say that frank but I think I may have failed to mention that the revs increase slowly a few seconds later. The stalling issue is not all of the time however. The idle of the car is lumpy and sometimes things like the fan kicking in at idle the car does feel like it wants to stall but then the revs increase albeit slowly. I have a delphi diagnostic laptop but I can't see anywhere on the screen the idle control position.
 
you would probably need nissan specific software eh alfie, ecutalk has freeware for the pre-coilpack engines (pollyp probably covered it in his blog)
the stepper motor type should give precise control really eh
 
pollyp said:
the alternators rotor bushes at the rear also have a finite lifespan. when they get worn down, it stops working which sometimes trigger the battery light and stops charging the battery, eventually the battery runs flat and whole car stops.
Click to expand...





That's what happened to my missus's car.....just stopped dead.
Alternator from the scrappy - fixed.
 

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