Y

yeoman

New Member
Hi People
Had my 1998 p38 4.0 SE since christmas very happy bunny everything works, I know I'am tempting fate. But being a completely ignorant of all things electrical I do have one question for all the experts on here.
When I first start the car the battery symbol is illuminated and the warning message alternater fault is displayed, blip the throttle slightly and both symbols go out and will not reappear untill I start it again. It has a new battery and that holds its charge. So I suppose my question is, is this a sign that the alternator is about to give up the ghost?
 
It would appear that the alternator is failing to charge until the revs rise, could be a bad connection, tick over too slow, or the alternator itself. Put a meter on the battery and measure the charge voltage, with the revs at 2000 you should see 14.2 to 14.8 volts.
 
yeoman said:
Hi People
Had my 1998 p38 4.0 SE since christmas very happy bunny everything works, I know I'am tempting fate. But being a completely ignorant of all things electrical I do have one question for all the experts on here.
When I first start the car the battery symbol is illuminated and the warning message alternater fault is displayed, blip the throttle slightly and both symbols go out and will not reappear untill I start it again. It has a new battery and that holds its charge. So I suppose my question is, is this a sign that the alternator is about to give up the ghost?
Click to expand...

May need new brushes and control unit soon.
 
I went through a similar phase before Christmas with my DHSE and Valeo alternator. A good diagnostic tool for £3 is a voltmeter plugging in to the ciggy lighter, like 130605564165 on Ebay. I had a new super sized battery but the alternator was only putting out 13.5 to 13.6 volts. Battery technology has changed since P38's were built and as Datatek says you need more than 14 volts to keep the battery charged and prevent sulphating. Have a read of this link CAR BATTERIES ARE NOT 12 VOLTS

I changed the alternator regulator to a 14.7v one, everything else with it was OK, and it now runs consistantly at 14.4+

It seemed a better move at £15 than a £80 to £300 replacement alternator that may still have a low set regulator.
 
When these vehicles show " Alternator Fault" is it taking that information from the alternator or is it picking it up from a low charge going to the battery?
 
Davlyn said:
When these vehicles show " Alternator Fault" is it taking that information from the alternator or is it picking it up from a low charge going to the battery?
Click to expand...

It takes it from the D+ line from the alternator that usually goes to the charge light on the dash. On the P38 this line goes to the BECM and the BECM lights the light on the dash. A bad connection on this line will cause the message as will the failure of the alternator to cause a voltage reversal on the line. Look at RAVE for more info.
 
Davlyn said:
Can the brushes and regulator be replaced will the alternators in situ?

thanks,

Dave
Click to expand...

Depends on where the alternator is located, but much easier on the bench where the inside of the alternator can be cleaned out and the bearings checked:)
 
cant wait to get my disc from Datatek so I can work out how to slacken the tensioner off to get the belt off the alternator.
 
Davlyn said:
cant wait to get my disc from Datatek so I can work out how to slacken the tensioner off to get the belt off the alternator.
Click to expand...

If yours is a P38 petrol all you need is a 15mm socket and ratchet. Put it on the centre nut on the tentioner and the whole unit moves away from the belt thus releasing it.
 
If it's a diesel you don't even need a socket or spanner ..just a lever bar over the top and through the hole in the top mount of the tensioner and lever downwards and hey presto the belt is off:)
 
jt_armstrong said:
Given that they rarely start when warm I suppose they will be quiet and economical...:D
Click to expand...
No plug leads or coil packs to fail and they don't go out of sync nearly as often as the V8:p:p:p Oh and mine starts instantly hot or cold with 107K on the clock:p:p:p
 
Datatek said:
No plug leads or coil packs to fail and they don't go out of sync nearly as often as the V8:p:p:p Oh and mine starts instantly hot or cold with 107K on the clock:p:p:p
Click to expand...

Other than a failed starter motor and a duff CPS the wife's P38 has never had an issue. Mine has worked like a dream for 2 years and only suffered from faults I caused:p
To be honest though I have never driven a diesel one so hard to comment other than in jest....:)
 
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