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Engine speed drop when using electrics

Discussion in 'A4/S4 forum(B5 Chassis)' started by Rich, Feb 23, 2007.

  1. Rich
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    Rich Rollin on boost mother hubbards

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    Just wondering if this is normal or anything to worry about as I have never noticed it in any other car I've had.

    Basically the easiest way to observe it is if the enginee is idling, stays about 900 rpm, if I then pull up the windows the engine speed drops to about 750-800, hear it start to struggle the the speed goes back up to about 1200 rpm, then drops down to 900. This happens if I do windscreen wipers or anythign really just not as noticeable.

    Probably nothing to worry about but why does this happen, surely the engine could just stay at a constant speed of 900rpm (like it would in any other car I've had), the battery voltages are fine although you can also see the needle drop slightly when you do this as well before going back up.
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  2. goon
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    goon Member

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    nothing to worry about it happens to all cars to a certain extent.it is all to do with battery capacity(aH),when the car is idling the alternator output is very low and the battery is doing all the work,just squeeze the accelerator a touch and you will see the voltmeter go up.think of being in a traffic jam-engine idling,heater on full,lights on,rear demister on,stereo on,the battery is having a hiding the current draw is massive,you need a good 20 minute run to recharge the battery to its normal state(about 13.5 volts).
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  3. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    Mine doesn't do this, your battery is probably on its way out as it obviously can't even cope with the small current drawn when putting the wipers on and is relying on the alternator to provide the extra current.
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  4. Rich
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    Rich Rollin on boost mother hubbards

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    Hmmm, thought that might be the case, then again the voltage always says like 14V :S. but also voltage != current so I guess it might be fecked, hasnt been replaced in 6 years. Will any standard 12V thing I get from halfords do the job?
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  5. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator

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    Pretty much yeah,as long as it's the right fitment,as the gap where the battery goes is a bit restrictive
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  6. shineydave
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    shineydave Member

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    all cars do it, try it in someone elses and see
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  7. Rich
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    Rich Rollin on boost mother hubbards

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    Hmmm, mixed opinions ;P

    Might see if I can borrow a newer battery to test just encase Andymac is right
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  8. scrupes
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    scrupes bloody great extension bodger

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    I'm not saying andymac is wrong, but i have experienced this in all my cars! esp when swithching rear demisters, blower fans or electric windows.???
    you've done well to get 6 yrs from a battery tho!
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  9. Lowlife
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    Lowlife German Hardcore

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    :iagree: Turning anything on that draws a lot of amps usually results in a momentary drop in engine speed but it should pick up again after a couple of seconds. As long as it recovers I wouldn't worry about it, if you are worried though get it checked out, most decent auto factors can check a battery and it'll give you peace of mind...
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  10. NineNails
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    NineNails Proud sponsor of the snack food industry

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    NO. Don't get a Halfrauds battery, they are *****!. If you love your car treat it to a Bosch Silver Top. Spec is 75Ah 729 Cold Crank, Bosch part No 7HN. The one I removed from my V6 was a Halfords brand less than 4 yrs old and knackered. It was only rated at 550 cold crank, under-powered in my mind. A cheapo battery is false economy I reckon. I paid £72 all in for mine from local Bosch agent.
    HTH
    Si.
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  11. Rich
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    Rich Rollin on boost mother hubbards

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    Cheers, at least I know that one will fit niceley as well.
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  12. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    If it's 6 years old the it'll definately need replacing.
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  13. Rich
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    Rich Rollin on boost mother hubbards

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    Right picked up a battery today, how do you get the battery out?! I can take off the lil cover that just slides off but then theres the big long black one that goes the length of the bonnet, blocking access to remove ones battery!
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  14. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator

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    That cover will come straight out. Pull the rubber seal that runs along the back edge and the cover will slide forward and off
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  15. Rich
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    Rich Rollin on boost mother hubbards

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    Reet, I installed the battery, got the Bosch 6HN in the end. First thing I noticed was changing gears as I reversed and drove out my road - it feels a lot more fluid and easier to press the clutch. not that it was hard before but its definatly a noticeable change -is the clutch electrically controlled or somthing? Also the steering felt a lot lighter to turn as well. Wasnt expecting those 2 things to happen so its def worth swapping the battery out if you think its getting on a bit.

    However - back to the original problem - the engine speed still dips when using electrics. ie idling at 900rpm, wind the windows and it drops to 700 before shuddering (head lits dim at the same time) and bringing the speed back up. I'm not sure if it takes a bit of time to "run in" the new battery tho, as I only had time to take it out for 15 mins.. I also remember reading it will of reset the ECU so might take a few miles to settle in completly anyway?
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  16. Sayre
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    Sayre Member

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    Sounds like your altenator is on its way out
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  17. NineNails
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    NineNails Proud sponsor of the snack food industry

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    It may be worth just replacing the regulator (it includes brushes)on the alternator. I think it's replaceable on your model. Cost me about £12 for mine. Hope you've not got worn slip rings.
    Si.
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  18. Rich
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    Rich Rollin on boost mother hubbards

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    Damn, I have no idea what a regulator/alternator or slip rings are really or how to replace it them..

    Anyone know a site where I can buy a replacemetn regulator/alternator? If it's cheap then I might as well just swap it out anyway to rule it out as a couple of people think it could be alternator related.

    Update: DOes this look like what I might need?
    http://www.car-stuff.com/audialternator.htm

    Or does anyone know any places in the UK I could order one from?
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  19. Rich
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    Rich Rollin on boost mother hubbards

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    Bump :p

    Anyone got any advice on the Alternator? Might pop into Camberley auto parts and see if they have one for a 1.8t
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  20. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator

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    I have a spare alt you could try, its from a non aircon 1.8t 70 amp jobbie
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  21. NineNails
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    NineNails Proud sponsor of the snack food industry

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    Hi. The 'slip' rings are the circular contact around the top of the spinning coil, they transfer the DC into the regulator via the brushes. On a 2001 car I doubt if they are worn, and thinking about my previous post I don't think the regulator/brush assembly is servicable on your model.
    Alternators are expensive to replace on a guess. You should get it tested first.
    Do you have a multi-meter? Here's what you do - start the car, make sure all the accessories are off and rev up the engine to a fast idle. Set the Voltmeter to the DC scale (not AC or Ohms). Measure the voltage across the battery terminals - red lead of the voltmeter on the positive terminal, black on the negative. The voltage should read around 14 volts. If it reads less than 12 volts you may indeed have a failed alternator and you can skip the next step. Next, turn on the heater, the rear window de-fogger, the radio, the headlights and anything else that draws power. Now rev up the motor and watch the voltmeter. It should still be reading around 14 volts. If it reads lower than 13 volts the chances are that your alternator is failing.
    Do this test before you go shelling out for a new one...It may not be the problem.
    Si.
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  22. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    Alternatively, trickle charge the new battery overnight, and if it continues to cause problems then it has to be the alternator - about £180 fitted at a specialist, or £400 from Audi.
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  23. Rich
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    Rich Rollin on boost mother hubbards

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    Well the car has a volt meter on the dash - when I start the car its on around 14V and drops maybe half a volt when loading it, at the same time the engine speed dips. When the idle speed recovers the volts go back up as well to the original position. Probably only a second from the speed dipping and volts dropping to recovering.

    I spoke to another couple of people who seem to say its nothing to worry about or it could be the alternator on the way out. I'd rather fix it sooner rather than later I guess I need to find a "specialist" in the Basingstoke area then that knows how to swap one out on my model to be sure. hmm
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