Should be an easy alternator question..

[Rpmayne 0]

What is the voltage supposed to be be across the battery at idle? Mines a VR6 and the voltage is 13.4v with no accessories on, and can go as low as 12v with everything on (excluding the stereo). I'm having many problems and wondering whether they are all linked to an unstable supply.

 

I thought the alternator should sustain 14v regardless of load from idle (600-700) upto max revs. This isn't the case, with everything on the volts can go as low as 12v at idle and when revved above 1k go back to 13.4v at best.

 

Thanks.

[flusted 0]

id stick the multi meter on battery to check reading as normal, then leave the live wire on mutlimeter but pick the earth feed up from the engine block or inlet. It should be the same reading, if lower then your earth strap needs cleaningreplacing.

[steveo29 0]

shouldnt really go under 13.5v ish with it all on...sounds like the brush pack /regulator is tired

[Reggit 0]

Dunno about the C alternator, but many don't properly kick in and start charging until engine is running at above idle speed, say 1.5-2k RPM. As long as it holds 13.5-14V with everything on at this sort of engine speed, I can't really see much of a problem.

 

But then someone who knows this car better than I will probably be along and say I'm talking rubbish. :)

[Rpmayne 0]

The reason I'm asking is primarily because of a stalling problem but also other strange symptoms which I thought may lead to a regulator problem;

 

- When on ignition before cranking over the fuel pump sometimes does multiple prime cycles. With the meter yesterday the fuel pump primed then stopped as normal. I then turn the lights on and the volts dropped below 12v and the fuel pump primes again. I just wonder whether dips on the supply are causing the fuel pump relay to start over.

 

- ABS faults intermittently appear, the latest is 00280 - Differential lock valve 2 (N126).

 

- With the engine at idle with all accessories on the illumination brightness is dim, and picks up to normal when revved over 1k. Surely this shouldn't happen?

 

The ECU is reporting a 00537 - Lambda regulation control limit not reached. Occassionally I have seen the value sit at 0.8 when idling, although the majority of the time it fluctuates as normal between 0.98-1.02. If at 0.8 then revved priefly it goes back to 0.98-1.02, sometimes staying there, sometimes dropping back to 0.8. Could this be because of the supply to the lambda / heater causing intermittent operation?

 

I dunno... maybe the Lambda is really dead but why the intermittent fuel pump priming and ABS faults?

[dr_mat 0]

- When on ignition before cranking over the fuel pump sometimes does multiple prime cycles. With the meter yesterday the fuel pump primed then stopped as normal. I then turn the lights on and the volts dropped below 12v and the fuel pump primes again. I just wonder whether dips on the supply are causing the fuel pump relay to start over.

 

- ABS faults intermittently appear, the latest is 00280 - Differential lock valve 2 (N126).

 

- With the engine at idle with all accessories on the illumination brightness is dim, and picks up to normal when revved over 1k. Surely this shouldn't happen?

 

The ECU is reporting a 00537 - Lambda regulation control limit not reached.

 

I dunno... maybe the Lambda is really dead but why the intermittent fuel pump priming and ABS faults?

 

Hmm. I think you have a faulty ABS valve block, a faulty lambda and a perfectly normal alternator... What spec alternator do you have? If your accessories can pull the voltage down so much you might consider getting a higher rated part? When you say "accessories" do you just mean the stuff as supplied from the factory?

 

TBH I can't say I've noticed that the voltage drops much when I let the VR6 idle, but I don't typically put that much electrical load on. Just the headlights if it's dark and that's it really. I can well imagine that if you put the heated seats on, the screen heater, the engine cooling fans, main beam headlights on .. that sort of thing, you're going to be pulling *comfortably* more than the standard 60A alternator can deliver, whatever the revs.

 

AFAIK the ECU considers 8v to be it's threshold. If you're seeing dips into the 11v range, this is not going to phase the ECU.

[Rpmayne 0]

I did get the part number off the alternator last night but I haven't got it with me. It's a genuine VW I bought about 3 years ago marked up as 90A/14v. I know it was a long shot but I have spent so much on things I didn't need (such as the alternator) that I just wanted to be sure.

 

Right, ordering a lambda after this message. Don't know about the fuel pump bit (very strange) but if I get it idling I'll be alot happier.

 

Thanks again.