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Thread: 01 B5 S4 Alternator/Electrical Problem

  1. #11
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    Quote Originally Posted by Bainos View Post
    With some further investigation, upon starting the car up it will idle at 12v on the voltage gauge but as soon as i rev it up to above 1500rpm just once the needle moves up to around 14v as if it was running correctly and then remains there until the car is shut off again and then repeated for each consecutive start. The red battery warning lights comes on upon startup along with the alternator warning on the colourMFA, and both stay on even once voltage has increased. It might be worth mentioning that the car starts each and every time without struggling which indicates to me that both the starter and battery are good? I did manage to start and drive the car a few times and it runs perfectly fine without any warnings and the voltage goes straight to around 14v even at idle but then after more consecutive starts back to getting the warnings.. Potentially thinking that the issue could be related to the alternator exciter wire?
    So your alternator has apart from the main charge lead a wire from the ignition and a small ground connection for the regulator? Basically should be a 3 wire alternator. Look on page 309 of the schematics I sent you.
    Current - 2007 B7 RS4 Avant, APR Stage 3, Milltek with Hi Flo Cats, GruppeM intake, Sachs Clutch, Factory Ceramics, JHM Shifter, RS6 FBSTW, AMI & Hi Res RSNE
    Current - 2012 B8 A4, 2.0T Quattro Avant SLine
    Current - 2001 B5 S4 Imola Yellow Avant
    Current - 1989 B3 90 Quattro - 7A NA Engine, (Long Term Restoration Project)
    Current - 1984 WR Ur Quattro

  2. #12

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    Quote Originally Posted by Tas_Audi View Post
    So your alternator has apart from the main charge lead a wire from the ignition and a small ground connection for the regulator? Basically should be a 3 wire alternator. Look on page 309 of the schematics I sent you.
    The alternator only has 2 wires, the main thick gauge power cable (B1+) and the single thin gauge blue exciter wire that plugs into the alternator.

    I didn't receive the schematics, must have missed me, I sometimes have trouble when new email addresses send me stuff to my Outlook, I will message you my Gmail which should work if you don't mind sending again.

    Sent from my Pixel 3 using Tapatalk
    Current: Nogaro 2001 B5 S4 Avant 6SPD - GET Stage 2+ Tune, Bosch 750cc Injectors, Walbro 450 Fuel Pump, Billy Boat 2.5" Catless Downpipes and Exhaust, APR R1 Diverter Valves, Bilstein PSS9 Coilovers, 034 Rear Sway Bar.

    Previous: Black 1999.5 A4 B5 1.8TQ 5SPD - Unknown Stage 1 tune, Turbo Back Exhaust, FK Coilovers, 710N Diverter Valve, Carbonio Intake

  3. #13

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    Some measurement taken last night with a DMM:

    - Voltage with car running at exciter wire plug (alternator end): 14.2v - This should rule out my theory of it being related to the exciter wire.
    - Voltage with accessories on at exciter wire plug (alternator end): 12.51v
    - Voltage at battery with accessories on: 12.52v
    - Voltage at battery when car has been started and idling before pressing accelerator: 11.98v
    - Voltage at battery car running: 14.18v
    - Voltage at battery after driving car for 20mins without shutting off whilst still running: 13.82v
    - Voltage at battery after driving car for 20mins after shutting off: 12.74v
    - Voltage at battery after driving car for 20mins with when accessories on: 12.54v

    The cluster voltage meter is showing approximately the same values as being read on the DMM. Something else to note is that whilst driving the car around for the 20 mins or so, the red battery light did go out at one point for 30 seconds or so but then returned again.

    The only real conclusion i can draw from the above testing is that the voltage measured at the battery when car is running dropped approx 0.4v after driving for 20 mins, is this normal and could it just be due to resistance from the entire electrical system heating up and losing some efficiency or the car itself heating up and having to run the fans to cool down and thus putting more load on the system? or is this an indicator that the battery is only accepting charge sometimes and may be the cause for this issue? I don't know if I am quite sure enough yet to fork out the money for another battery, I will have to find a suitable one locally that I can borrow for testing.
    Last edited by Bainos; February 18th, 2020 at 11:37 AM.

  4. #14

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    Disregarding all the exciter wire and accessories on issues that really cloud the basics, If your battery voltage BEFORE starting the car is 12.5v and is >14v running then the alternator is (mostly) charging the battery. The voltage on shut down contains a surface charge that will dissipate and if, when settled, it's 12.6 plus v then it's fully charged by an Alternator. The voltages that you have don't gel with the battery light being on most of the time. IF your battery voltage is 12.5 before start, then the battery is holding voltage so the battery isn't terminal at this point.

    What do you mean by - Voltage at battery after driving car for 20mins with when accessories on: 12.54v - Car running or not. If it is running then it's not great. You are complicating the issue at this point. Initially what you need to know is if the battery gets charged and is holding it's charge. If so then your basic charging system and battery are working for most of the time. It seems to be, as your battery would hardly be well charged after 20 mins driving if the charging system was performing like your battery light is suggesting. The electrical consumption in these cars is fairly significant as you alluded to early on when it seemed to have low voltage. Did you ever confirm that?

    Then to move on to the battery light and the voltage after start at idle before increasing RPM. That voltage you took, was it across the battery with a DMM or a gauge in the car? It's the sort of voltage the battery would expect to see on start.

    Clearly you have a problem, accepted. What frustrates this diagnosis from a distance stuff is not getting the info in clear form. You don't want additional load on the battery as it's variable and not a specific figure.

    Currently I see that the state of charge and the battery light on don't tally. (If the light highlights another problem other than low/no charging then it may be correct)
    The steady low voltage directly after starting is interesting but only if that is measured with a DMM at the battery, not the gauge. My cars Volt gauges drop down to maybe 10.5 - 11 V indicated as the starter is turning, then back to a hair over 12v on start and within 1-2 seconds moves up to ~14v. Only across the battery will tell the true voltage. There may be an issue with your gauge too.

    My suggestions, either get a disciplined approach to fault finding and map out a path of analysis and stick to it or find a good auto electrician. We'll all probably learn something from this as we do with most things and it would be good if we could without undue head banging.
    C5 RS6: APR, Milltek & Wagner -- B5 RS4 : tastefully modified -- Audi 1.8 quattro 132 Kw -- UNIMOG 404 TLF8

  5. #15

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    Quote Originally Posted by IchBautAuto View Post
    Disregarding all the exciter wire and accessories on issues that really cloud the basics, If your battery voltage BEFORE starting the car is 12.5v and is >14v running then the alternator is (mostly) charging the battery. The voltage on shut down contains a surface charge that will dissipate and if, when settled, it's 12.6 plus v then it's fully charged by an Alternator. The voltages that you have don't gel with the battery light being on most of the time. IF your battery voltage is 12.5 before start, then the battery is holding voltage so the battery isn't terminal at this point.
    All voltages in my previous post were measured using a DMM and at the battery terminals themselves. Battery does seem to be holding charge, never has a problem starting up i.e. hesitation or having to turn it over many times before it fires. My understanding is that the battery light can come on and be red (indicative of a fault with the alternator/starter motor etc) or yellow (indicative of a low battery charge or flat battery etc).

    Quote Originally Posted by IchBautAuto View Post
    What do you mean by - Voltage at battery after driving car for 20mins with when accessories on: 12.54v - Car running or not. If it is running then it's not great. You are complicating the issue at this point. Initially what you need to know is if the battery gets charged and is holding it's charge. If so then your basic charging system and battery are working for most of the time. It seems to be, as your battery would hardly be well charged after 20 mins driving if the charging system was performing like your battery light is suggesting. The electrical consumption in these cars is fairly significant as you alluded to early on when it seemed to have low voltage. Did you ever confirm that?
    Voltage at battery after driving car for 20mins with when accessories on: 12.54v, the car was driven for 20 minutes then the engine was switched off but the key was turned to accessories (i.e. all electronics still powered and illuminated) instead of completely off (i.e. key completely removed). When you refer to confirming about the electrical consumption, do you mean the battery getting load tested? This was done, came back good just a little low on volts (likely due to it not getting charged and me starting the car many times).


    Quote Originally Posted by IchBautAuto View Post
    Then to move on to the battery light and the voltage after start at idle before increasing RPM. That voltage you took, was it across the battery with a DMM or a gauge in the car? It's the sort of voltage the battery would expect to see on start.
    Voltage after start at idle before increasing RPM, is the voltage I measured using a DMM again at the battery with the engine running without me touching the throttle, as soon as i touch the throttle and rev the car to 1500rpm the voltage jumps from this value (11.98v) up to 14.18v (measured at the battery terminals using DMM) and stays there for the duration the car is running. This jump in voltage after blipping the throttle is what got me thnking about the exciter wire and whether there was an issue with that, which there does not seem to be.

    Quote Originally Posted by IchBautAuto View Post
    Currently I see that the state of charge and the battery light on don't tally. (If the light highlights another problem other than low/no charging then it may be correct)
    The steady low voltage directly after starting is interesting but only if that is measured with a DMM at the battery, not the gauge. My cars Volt gauges drop down to maybe 10.5 - 11 V indicated as the starter is turning, then back to a hair over 12v on start and within 1-2 seconds moves up to ~14v. Only across the battery will tell the true voltage. There may be an issue with your gauge too.
    This was measured with a DMM at the battery, so it appears the gauge and the true readings with a DMM at the battery are showing approximately the same values in all instances.

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