Failing alternator, bad earth or something else?

[Will Rose MS]

My Legnum has developed a fault over the past couple of days so I thought I'd post the symptoms here first to see if anyone has experienced anything similar, so here goes:

* Radio stopped working
* Central locking stopped working (the aftermarket toad alarm still works and has since started beeping when locking the car)
* The backlighting on instrument cluster is erratic and quite randomly dims and brightens, when breaking or putting into drive for example
* Not sure if related but I've occasionally been hearing kind of a relay sounding clrackling around the inlet manifold/throttle body area
* Also noticed struggling on idle and even stalled once
* The gear changes in auto mode are not what they used to be like, hesitating, sometimes rough changes

Carried out a battery/alternator test - battery fully charged and spot on under cranking. Alternator charging ok with no load but drops when I turn headlights on. So suspect the alternator but why would this interfere with central locking etc when the engine isn't even running?
Removed battery earth lead while ticking over - no change, not stalling with headlights on etc.
Or could it be a slippy belt? I've ordered one anyway as it looks like it could do with changing..


Any inputs would be appreciated..

[Davezj]

when you say the battery/alternator test was OK what did you test and what were the voltages (roughly)

engine off battery voltage?
headlights on engine off battery voltage?
engine running battery voltage?
engine running headlights on battery voltage?

it always concerns me when someone say i have tested this and it is ok. but does not give any details of the test.

i don't know how competent you are at spannering so forgive me for asking these question.
there are plenty of people that have cars and can measure a voltage and say,
1. 12V that's OK.
or
2. i need 12V but the higher the charging voltage the better.

both statements are wrong and can be a symptom of an issue. but if somebody say i have tested it and it is OK we can only take your word for it. and go down another possibly more expensive route.

we only know what you tell us. so the more info you can give the better when diagnosing an issue.

[Will Rose MS]

Sorry..I should have put some figures in before but here they are now:
Engine off, lights off 12.7V
Engine off, lights on 12.4V
Engine running, lights on/off altering between 14.05 and 14.3V

I also noticed the belt end of the engine getting a bit noisy when I turned lights on. The dash lights dim out mainly when I first turn lights on but brighten back up when I even lightly touch the throttle pedal, and then dim out when the car gets static after breaking..this is also when it idles quite low

[galantnight]

this is also when it idles quite low ?

What are you saying is low, below 600 rpm ?? is it ok when you first start up ??

[Will Rose MS]

Well I just started it up and it idles fine when cold..around 900rpm (which I assume should be normal when warming up?) The backlighting worked fine as well with no flickering..and central locking worked ok as well while the turbo timer kept engine running. However the noise at the belt end of the engine is still there when alternator gets a load (lights and heater on)..

[Davezj]

1200-1500rpm is cold idle, when it starts to warm up it should drop to about 650rpm at idle and when in drive i think idle should drop to 600rpm.
these values are set in the ecu tables.

but at normal stationary idle in Neutral with air con on the idle should increase to about 900 rpm when the air con switches on.

[galantnight]

Well I just started it up and it idles fine when cold..around 900rpm (which I assume should be normal when warming up?) The backlighting worked fine as well with no flickering..and central locking worked ok as well while the turbo timer kept engine running. However the noise at the belt end of the engine is still there when alternator gets a load (lights and heater on)..

But what was the idle when it warmed up ??

[Will Rose MS]

Started up today on a cold morning:

* Warm up starts at 1400 rpm and quickly rises to 1450 rpm
* Gradually drops while warming up
* At 1100 rpm instrument lights dim out and the noise from belt end of engine starts to appear
* At 1000 rpm noise is getting louder and worsens when I turn lights on
* At 850 rpm temperature on 1/4
* Idle at 700 rpm when warmed up, drops to 650 when in Drive

Not sure where exactly to place the noise yet but will get the front end up later today to have a good look underneath and check for any play in pulleys etc.

[Will Rose MS]

Here's a link to a video I took last night. First 6 seconds is just idling, after that I turned the lights on..
https://www.youtube.com/watch?v=eCsaoEGIWsY

[Davezj]

Sorry..I should have put some figures in before but here they are now:
Engine off, lights off 12.7V
Engine off, lights on 12.4V
Engine running, lights on/off altering between 14.05 and 14.3V


these values seem OK so the battery and charging system seem to working correctly.

i am not saying there is not another electrical issue.
maybe as you mentioned above some kind of bad earth somewhere.
i believe the alternator has a direct power feed wire to the battery. the earth for the alternator goes back through the engine block and chassis. do you have the braided wire strap from the plenum chamber to the chassis connected, worth checking.

as for the rest of the stuff not working i would check the fuses. and don't just visually check them test them with a resistance meter. i have seen fuses that looked ok with a quick pull out and glance and put back in but only to find out later it had blown right next to one of the legs and could not be seen very well.

[Will Rose MS]

Just changed alternator belt (it was ready for changing for sure) and the noise seems to have gone..at least for time being. Also checked the alternator pulley and tensioner - no play or rumble there. Rest of the issue still remains. Will order a new AC/PS belt for weekend and have another look when it comes to changing it.

Checked and cleaned earths behind battery and from plenum chamber - they seem ok. Fuses got checked first thing, no issues there.

Is there any more earths to check besides the ones mentioned above?

[Nick Mann]

That's the earth's. Strap from battery to engine via chassis and the plenum one.

Have you checked the bolts on the cable terminations in the engine bay fuse box?

[Davezj]

Will,
An easy thing to do is measure resistance from negative battery terminal and the alternator case, it should be not more that about 1-2 ohms above the resistance of the leads. so check the leads to start with.

[Will Rose MS]

Started tracing back my steps in what I've done to the car over the past month. Changed spark plugs recently so the earth strap from manifold had to come off; got it off again to check the resistance in it - all looked good but the terminals were a bit corroded - gave them a good rub and clean, refitted and it's sorted now.
Still get a slight drop on heater backlighting when I turn headlights on but everything else is working as it should.

[elnevio]

Wonderful! Thanks for letting us know. These sort of fixes are nice, but they help everyone as these cars get older and the longer term issues appear more regularly. :)

[Davezj]

Started tracing back my steps in what I've done to the car over the past month. Changed spark plugs recently so the earth strap from manifold had to come off; got it off again to check the resistance in it - all looked good but the terminals were a bit corroded - gave them a good rub and clean, refitted and it's sorted now.
Still get a slight drop on heater backlighting when I turn headlights on but everything else is working as it should.

I hope realise that the instrument illumination is designed to dim when the headlights are turned on. And there is a rotary wheel/switch next to the lower right hand side of the rev counter cluster to control the brightness of the back light.


Sent from my space-aged gizmo

[Will Rose MS]

Sent from my space-aged gizmo

I know the instrument lights are dimmable but it's actually the backlight on heater control that dims out when I turn lights on, the instrument lights remain the same..

[Davezj]

all the dash back lights dim when the lights are turned on, the heater control the cigarette lighter the centre console lights all of it. the only one that does not is the dash clocks because they have there own dimmer wheel.

it is the same on every car i have own, ford's, rover's, austin's, vauxhall's, etc.