P38A Alternator Problem?

tank93 · Oct 18, 2020

Driving home yesterday and suddenly started to get messages on the IPK, gearbox fault, alarm fault etc then the ABS light came on, then the speedo and tacho started going all over the place then the IPK stopped working, I thought the engine had cut out but it was still running, however around a mile later everything died and wouldnt restart, battery was flat! Rang RAC for recovery, whilst waiting (after 20mins) I managed to get her started and limped the 2 miles back home (guess the battery recovered)! Got home, came back out an hour later, started the engine, multimetre across the two battery terminals and voltage was dropping so guess that means my alternator has given up!

My car is a V8 (1997) so fitted with the GEMS engine, alternator says Denso A127-120 on it. I would like to try and refurb the alternator myself. Can anybody recommended where I can get hold of a repair kit from please? Have read a few posts on here and read about alternator set point - 13.8 or 14.2v? What is that all about and what do I need for my car and how can I ensure I get the correct set point? Thank you

kermit_rr · Oct 18, 2020

Have you charged the battery up off the car? What voltage does the battery show once fully charged and left to settle? What is the actual voltage when the engine is running?
Most, if not all modern batteries required the higher charging voltage

RangeRoller dt · Oct 18, 2020

There’s a voltage regulator in the back of the alternator, in the 90s they used 13.8v set points but batteries have changed now. Most of us swap out for a 14v one. Is about £12

kermit_rr · Oct 18, 2020

While you're at it, no harm in checking the AC side to make sure the windings, brushes etc are good

dubbleRR · Oct 18, 2020

Check the main feed from the alternator ,,,,,continuity

and battery terminals are tight and earth points .... If you can check the voltage at the back of the alternator when the engine is running if its more than at battery terminals ,,,Corroded wire terminals

.....RR.

Grrrrrr · Oct 18, 2020

dubbleRR said:
Check the main feed from the alternator ,,,,,continuity and battery terminals are tight and earth points .... If you can check the voltage at the back of the alternator when the engine is running if its more than at battery terminals ,,,Corroded wire terminals .....RR.

+1. Early GEMS had an issue with earth points, iirc.

Worth having a sniff in the fusebox too.

tank93 · Oct 18, 2020

Went outside this morning, checked the battery voltage and it was 12.4, started the engine and watched the voltage on my multimetre dropping, when it got to under 10v I switched the engine off before it cut out itself. Soon as the engine is switched off the voltage on the multimetre starts to head back up towards 12v. The two connections on the back of the alternator are tight as are the connections on the battery. I did put my multimetre on the the connection at the back of the alternator when the engine was running and the voltage was less than at the battery terminals.

Anyway ive removed the alternator as its only a 15 min job, just need a replacement now.

How can I tell if the alternator has a 13.8v or 14v set point? If its only £12 its a no brainer for when I get a new alternator. Where do you buy the 14v voltage regulator from, does anybody have a link to a site?

Thanks for all the help/advice

Tenebreaux · Oct 18, 2020

tank93 said:
Went outside this morning, checked the battery voltage and it was 12.4, started the engine and watched the voltage on my multimetre dropping, when it got to under 10v I switched the engine off before it cut out itself. Soon as the engine is switched off the voltage on the multimetre starts to head back up towards 12v. The two connections on the back of the alternator are tight as are the connections on the battery. I did put my multimetre on the the connection at the back of the alternator when the engine was running and the voltage was less than at the battery terminals.

Anyway ive removed the alternator as its only a 15 min job, just need a replacement now.

How can I tell if the alternator has a 13.8v or 14v set point? If its only £12 its a no brainer for when I get a new alternator. Where do you buy the 14v voltage regulator from, does anybody have a link to a site?

Thanks for all the help/advice

This is for the diesel, not sure if it's the same for the petrol.
https://www.ebay.co.uk/itm/Alternator-Regulator-MOBILETRON-VR-VW010/352317681762?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
Courtesy of @brianp38dse

tank93 · Oct 18, 2020

Ok thanks, never had a diesel so no idea if its the same alternator/regulator as a petrol

tank93 · Oct 20, 2020

Fitted a new alternator today, car starts and runs great now!

At idle I get 14v at the battery terminals, when I switch on the lights, heater, heated screen the voltage drops to 13.6 regardless of whether the engine is at idle or 2000rpm.

Is this voltage sufficient to charge the battery or do I need to upgrade the voltage regulator? If it helps battery I have fitted is a Yuasa 664HD.

Thank you

tomcat59alan · Oct 20, 2020

tank93 said:
Fitted a new alternator today, car starts and runs great now!

At idle I get 14v at the battery terminals, when I switch on the lights, heater, heated screen the voltage drops to 13.6 regardless of whether the engine is at idle or 2000rpm.

Is this voltage sufficient to charge the battery or do I need to upgrade the voltage regulator? If it helps battery I have fitted is a Yuasa 664HD.

Thank you

Personally I would change it, remember we're coming up to dark days

RangeRoller dt · Oct 20, 2020

was handy when Data would correct me

kermit_rr · Oct 20, 2020

Just been out in mine and obd reported 14.7v. after a bit of a drive it reports 13.8v and drops a bit more when i put lots of things on. Seems to charge the battery ok

tomcat59alan · Oct 20, 2020

RangeRoller dt said:
was handy when Data would correct me

Only when you needed to be.

kermit_rr · Oct 20, 2020

RangeRoller dt said:
was handy when Data would correct me

He's not real. Warp drive isn't real either. Sorry dude

Mark Piercy · Oct 21, 2020

kermit_rr said:
He's not real. Warp drive isn't real either. Sorry dude

Jim... She cannee handle it!!!

RangeRoller dt · Oct 21, 2020

That’s what they said about the communicators but iPhone is way better and you can make it do the chirp chirp thing

kermit_rr · Oct 21, 2020

RangeRoller dt said:
That’s what they said about the communicators but iPhone is way better and you can make it do the chirp chirp thing

iphone is way better!?
don't be a silly billy

RangeRoller dt · Oct 21, 2020

Better than the beep de beep thing Shatner had but will smash to bits if you drop it in a laser fight

Ratae · Oct 21, 2020

tank93 said:
Fitted a new alternator today, car starts and runs great now!

At idle I get 14v at the battery terminals, when I switch on the lights, heater, heated screen the voltage drops to 13.6 regardless of whether the engine is at idle or 2000rpm.

Is this voltage sufficient to charge the battery or do I need to upgrade the voltage regulator? If it helps battery I have fitted is a Yuasa 664HD.

Thank you

Hopefully you fully charged the battery with a battery charger before starting with the new alternator?
I've posted this several times in various threads:
https://www.optimabatteries.com/en-...nators-are-not-designed-charge-dead-batteries
Disregard the redtop/yellowtop/blutop advertising in the last paragraph.

P38A Alternator Problem?

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