P38A charging

2000,p 38 diesel .
my alternator light goes out but the battery runs flat and my meters say 12.5.volts so i changed the alternator out for a new one ,still the same problem
anyone have any ideas please?

Is that 12.5 when running or engine off?
Put a volt meter between the +ve post on the alternator and the alternator body with the engine running, see what you get then. There should be a smaller wire too, make sure it's connected

The diesel alternator can be up rated to charge at 14,7v with a new mobllitron regulator for about £15 that may help things and is a worth while swap
i will look up the number of it if needed

If that is 12.5 volts with the engine running, check the earth link from engine to chassis. To test, you can put a jump start lead from the battery negative to the engine block.

many thanks for the replies
its 12.5 with the engine running . I have one of these cheap lidl/aldi battery testers it says 1/2 charged but none of the charging lights come on at all . Checked on my rover 75 car and it works fine on there.
I checked the voltage ith the engine switched off 12.5 on the big alternator terminal to the battery negative and to a good earth . No reading on the small terminal.
Engine running 12.4 v on both terminals but the lidl device still says no charge .
It was supposed to be a brand new alternator still in the box bought new last year and kept in my garage .
Is there any way i can check the alternator off the motor ?
years ago you used to feed positive power to a 2.2 w bulb then through the bulb to the alternator small terminal then connect the big one to the battery positive ,earth the alternator body to the same battery ,turn the alternator with a drill ant see if the voltage rise .
Seems odd the old one wasnt charging and now the new one not charging .
BTW auto eletrician shops thin on the ground around here .
As an aside she wont idle nicely at low revs 750 indicated sounds as though shes not running on all cylinders and rattles like big ends at the front of the engine knocking . Oil changed every 15000 miles and filters . with the serpentine belt off no rattles and no misfiring . The noise seems to come from the front of the engine .
its a 1999 manual diesel 146,000 miles .
I see on here someone said it could be the dual mass flywheel giving the crank wrong signals ? cant see why that is when the rattle ,hunting dissappears with the belt off.
Any,all help GRATEFULLY received

If the charge light doesn't come on with the ignition, sort that out first.

rover75lover said:

many thanks for the replies
its 12.5 with the engine running . I have one of these cheap lidl/aldi battery testers it says 1/2 charged but none of the charging lights come on at all . Checked on my rover 75 car and it works fine on there.
I checked the voltage ith the engine switched off 12.5 on the big alternator terminal to the battery negative and to a good earth . No reading on the small terminal.
Engine running 12.4 v on both terminals but the lidl device still says no charge .
It was supposed to be a brand new alternator still in the box bought new last year and kept in my garage .
Is there any way i can check the alternator off the motor ?
years ago you used to feed positive power to a 2.2 w bulb then through the bulb to the alternator small terminal then connect the big one to the battery positive ,earth the alternator body to the same battery ,turn the alternator with a drill ant see if the voltage rise .
Seems odd the old one wasnt charging and now the new one not charging .
BTW auto eletrician shops thin on the ground around here .
As an aside she wont idle nicely at low revs 750 indicated sounds as though shes not running on all cylinders and rattles like big ends at the front of the engine knocking . Oil changed every 15000 miles and filters . with the serpentine belt off no rattles and no misfiring . The noise seems to come from the front of the engine .
its a 1999 manual diesel 146,000 miles .
I see on here someone said it could be the dual mass flywheel giving the crank wrong signals ? cant see why that is when the rattle ,hunting dissappears with the belt off.
Any,all help GRATEFULLY received

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So the alternator is definitely not charging. This could be caused in the case of the P38 by a bad connection from the D+ terminal to the BECM which provides the exciter voltage to start the alternator charging.
Take the wire off the D+ and connect a small bulb from the D+ to the battery positive, it should light, if it does, start the engine and see if the light goes out. If it does, check the voltage again at the battery and see if it rises. If the bulb does not light, check the engine to chassis earth. If it lights but does not go out when you start the engine, either the alternator is duff or again the engine to chassis earth is suspect.

I would change the oil and filter more often than every 15k, more like every 5k.

aj1954 said:

I would change the oil and filter more often than every 15k, more like every 5k.

Click to expand...

+1 do mine every 4 months and I only do 4k to 5k a year

N that rattle ,knocking from the front end might be the crank damper ,,,,the big pulley at the bottom the belts go on there rubber and break up ,,,

÷1to the crank damper that can make a terrible noise like a big engine knocking

Sorted now ,Thanks to you guys on here so thank you again .
the main problem was the crank damper ,he actual ribbed part had separated from the center piece so would rotate with the crank pulley but not at enough speed if it encountered any real resistance ,i.e. steering pump .alternator etc .
Pulled one off my old engine i had here ,refitted and now im rattleless ,YiPPEE.
The alternator is showing charge so i swapped the old one back on and it works as well . I think the belt even though you could see it turning wasnt turning fast enough to allow the alternator to work .
THANK YOU GUYS ,AWESOME AS EVER