dodgy alternator

hi again guys my p38 diesel message center has flashed up gearbox fault and alternator fault a few times over the past few days and when using it at night the dash lights keep going up and down in brightness what is the chances of the alternator playing up, I took it to a place today and asked if they could check and the bloke said "that there is to much to go wrong inside one for those vehicles and if its a intermittent fault he probarly wouldnt pick it up but I can do you a new alternator for £195 thats what you get for owning a range rover" So I walked out, is there any easy test to do to find out if it is playing up thanks

didn't he check it anyway? if he didn't he's a ****!! to find out exactly whats going on you need to get it thoroughly tested but again that will cost. maybe you could try a s/hand alternator thats know to be good. i'm sure someone will be along to tell you how to test it tho!!

Just a thought....perhaps check your battery first, as these messages do have a habit of popping up when the battery is slightly below par. Any battery franchise can do a battery load check for you quickly and usually free. Even the slightest drop in charge can cause P38s to behave in a very untoward manner......if its the battery, fitting a new one will remove the messages completely. You could also swop the battery out with one that you know to be 100% and see if the messages vanish......
This cold weather this winter has killed many a battery that was functioning quite well in the autumn....

the bloke didnt even bother to check battery or alternator I think batterry is good only brought it last year and never missed a beat even when it went to -7 one morning when i went to work, have asked my old man if i could try the alternator from his p38 but the meanie said no as all he would get back is my old one(dont know what he meant lol), but can get a new 1 from fleabay for £90. so me thinks i got to find someone who will check mine and take it from there

Don't buy one from Ebay. I bought a new one 10 days ago which was faulty, still trying to get them to do something. Pay a little more and get a quality replacement.

Re-con your alternator, new diode pack, brushes and regulator. Save you a bundle.

Check the output yourself with a multimeter. You can get them for £5 or £6. When running you should get a reading of 13.5 to just over 14 Volts. Switch on lights and rear window etc and it should still be about the same and certainly over the 12.5 mark. Resting Voltage at the battery itself with no load is ideally 12.6 but experience shows 12.2V is normally still ok (in good weather). If it drops to below 12V when running then suspect the alternator. A repair kit is not too daunting a fix.

If you don't feel up to doing it yourself, your local Auto Electrical specialist will recon your alternator for you for a fraction of the price of a new one. But do some basic checks first as Hippolover suggests above. I'd say you should get more than 14V though when running, especially above idle.

hippolover said:

Check the output yourself with a multimeter. You can get them for £5 or £6. When running you should get a reading of 13.5 to just over 14 Volts. Switch on lights and rear window etc and it should still be about the same and certainly over the 12.5 mark. Resting Voltage at the battery itself with no load is ideally 12.6 but experience shows 12.2V is normally still ok (in good weather). If it drops to below 12V when running then suspect the alternator. A repair kit is not too daunting a fix.

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Dont bother - you can only test no-load conditions. Get it tested with the proper gear by a battery place or halfrauds.
If YOU want to do it proper - read the correct way to do it in the Q's and A's section.

Had a similar problem on mine a few years back..lights "Pulsing" in sync. with engine speed.
Checked voltage and it was surging up to 18.5 volts..not good for the electronics on a p38.
Fitted a new alternator, problem solved.:behindsofa:

By doing the checks above I discovered a car I once had was putting out about 18 Volts then down to about 8 then zero so it does work. I agree it is 'no-load' as such however its a fairly good indicator something is amiss (especially if you do apply a load by switching various things on).

(Maybe 14.5 Volts rather than 14 is about as high as I would like to see a reading using the above technique.)

How do yu check the rectifier aint putting out too much ripple and that the alternator puts out current?

Do a full run on a rig with all the meters and wires connected and apply loads etc etc but if all you have is an ordinary meter then like I say you'll get an indication that something is wrong and therefore worthy of further investigation. It's only advice. I took an alternator into a specialist auto electrician's once for him to attach it to his bench, run it up, look at the figures only for him to take it off, chuck it in the corner and tell me it was 'Frocked' (or something like that). Since then I've done my old d.i.y trick before taking it further. I don't delve into rectifiers too much since a friend of mine told me his motor bike's rectifier packed up reversed its polarity, fried his alternator and parts of his anatomy directly above it. :flame2:

To check for AC ripple from the alternator that would show the diode pack is shot you really need an oscilloscope, a scope can also be useful to show regulation problems. Alternators vary quite a lot but at about 2k rpm on the alternator you should expect 14.5 to 14.8 volts at the battery if the battery is fully charged and in good condition. A battery with an internal short will hold the voltage down and the battery will quite likely get hot.

hippolover said:

Check the output yourself with a multimeter. You can get them for £5 or £6. When running you should get a reading of 13.5 to just over 14 Volts. Switch on lights and rear window etc and it should still be about the same and certainly over the 12.5 mark. Resting Voltage at the battery itself with no load is ideally 12.6 but experience shows 12.2V is normally still ok (in good weather). If it drops to below 12V when running then suspect the alternator. A repair kit is not too daunting a fix.

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Had it checked at rest it was 12.5v and when running it went to 13.4v and under load it stayed the same at 13.4 is that enough to keep it ok or does it need sorting out as dash lights etc pulse bright and dim every now and again

no
get it checked on load at Halfrauds - or similar. its free.

The Mad Hat Man said:

no
get it checked on load at Halfrauds - or similar. its free.

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I wouldn't trust Halfords numpties to test load an alternator, go to an auto electrical factors that rebuilds/tests starters and alternators on site.

You could of course do a limited test yourself but you will need a multimeter plus access to an electronic amp clamp, that can read DC current.