New alternator causing electrical buzz

[Ginothy]

Hi everyone, having just managed to get the new alternator switched over with the defunct old one I now have another problem. Whenever I rev the engine lots an electrical buzzing noise starts on the dashboard and it doesn't stop until I stop the engine. I've read somewhere that this may be something to do with the battery not dealing properly with the spikes of electrical energy coming out of the alternator? I'm not driving it for the time being until I work out what this problem is.

I was assured by the people I bought the new alternator from that it was the correct type. I'm worried they might have been wrong. Would deciphering the amperage of the alternators confirm they're a match? If so how do you work that one out (considering the old one doesn't do much)? I'm certain it's wired up properly, and the connections all appear fine. What might the problem be if it is not to do with a wrong part?

The other thing I'm wondering about is that the section of the mounting bolt hole on the new alternator is slightly different (larger protrusion) from the old one meaning the alternator is very slightly twisted in its housing, which means the belt is again very slightly misaligned. Will this develop into a serious problem or is it normal? Seems to turn fine when the engine is running.

Cheers for your help

Tim

P.S. I might need jargon explaining to me if this gets really technical.

[big red bus]

do you have a surpresor fitted?
alternator should bolt up same as old one. If running out of line, will destroy the belt and you will be stuck many millions of miles from home. Does the out side housing look identical to the one removed?

[Ginothy]

No, no suppressor. The out side housing looks almost completely identical apart from that one bolt hole, i.e:

IMAG1302.jpg

The fixing in the top right of the photo on the old alternator shown is flat on the opposite side, on the new alternator it's raised on the opposite side like in the picture. That make sense? Hence the new one is levering away from the mounting bracket slightly.

New mounting bracket? Change the alternator?

[ghost123uk]

Whenever I rev the engine lots an electrical buzzing noise starts on the dashboard and it doesn't stop until I stop the engine.

This is the thing called a "B.O.D." or "Buzzer Of Doom" it is part of the oil pressure monitoring system.
Your problem is very likely the wire that monitors the engine RPM and if the oil pressure is low at above 2,200(ish) RPM sounds a warning buzzer. When you fitted the alternator you probably disturbed this wire (From the "w" terminal on the alternator (wire is black with red stripe, I think), if I recall correctly). Should be an easy fix.

I've read somewhere that this may be something to do with the battery not dealing properly with the spikes of electrical energy coming out of the alternator?

Well don't read that book again !

I'm not driving it for the time being until I work out what this problem is.

Sensible

Would deciphering the amperage of the alternators confirm they're a match? If so how do you work that one out (considering the old one doesn't do much)?

Any alternator that fits and has the correct wires will work fine. Anything from 45 Amps to 90 Amps = Fine. The only difference a higher Amp rating makes is how fast it will charge up a flat battery (unless you have lots of big spotlights etc when you then would need a high power alternator to cope with powering them).

The other thing I'm wondering about is that the section of the mounting bolt hole on the new alternator is slightly different (larger protrusion) from the old one meaning the alternator is very slightly twisted in its housing, which means the belt is again very slightly misaligned. Will this develop into a serious problem or is it normal? Seems to turn fine when the engine is running.

This was talked about a couple of days ago on here (do a search). Not sure what or why, but it ain't correct and needs looking at or you run the risk of damaging the belt or alternator bearings. I think a bracket with a kink in it was mentioned (likely you could bend a suitable kink into your bracket given a big strong vice and the correct bending tools, ( a hammer ))

Let us know how you get on Tim

p.s. = look in our wiki knowledge base, (at the top of every page on here) esp re the buzzer wiring

[Mocki]

firstly, check you didnt disturb the two brown oil pressure sensor wires in the engine bay when changing the alternator.

if it is ok at tickover , but buzzes doom after revs reach 2000 rpm then check the brown wire and sender behind and below the waterpump pulley, my guess is you caught it when putting the belt on, and its disconnected or broken.

[Ian Hulley]

firstly, check you didnt disturb the two brown oil pressure sensor wires in the engine bay when changing the alternator.

if it is ok at tickover , but buzzes doom after revs reach 2000 rpm then check the brown wire and sender behind and below the waterpump pulley, my guess is you caught it when putting the belt on, and its disconnected or broken.

^^ Agreed, mine came on once when an alternator belt came off. There should be a thin cable tie holding the brown wire and it's right angled spade terminal to the sensor, that's why the sensor has a groove running round it.

Ian

[Ginothy]

Cheers all, first class advice! Will get on it when I get home from work...

[Ginothy]

Right well new update, new question. i.e. problem still not resolved. Finally got around to getting my alternator bracket off to the smithy to have it altered (had no cash for it until pay day) and have fitted it so now the belt is all nicely aligned. So that bit is fine.

However, I checked over the black and read wire to the W terminal on the alternator and it was plugged in ok but the spade connector seemed a little loose so assumed (hoped) this was the problem. Having made sure that connection is now all fine and dandy the BOD is still going off. There is one other blue wire coming from the same sleeve as the black and red one which is not connected (see pic), as it never was on my old alternator.

IMAG1404.jpg

So my question is, should this be bolted onto the alternator at the other available connection? I haven't tried this as I'm a little worried that doing so will short out and ruin my brand new alternator.

Or is the problem elsewhere? i.e. actually a problem with the oil pressure? (starting to understand why it's called the BOD).

There is a slight leek coming from the dip stick connection. The washer was replaced last time I had it serviced but there still seems to be a 'healthy' amount of oil around the connection with the engine block. The wiki doesn't seem to answer these questions but admittedly I haven't spent too long searching through it.

Cheers all for your help

Tim

[Mocki]

what engine is it?
i was (and shouldnt have) assuming it was a petrol WBX but now i see your reference to the "W" connection i realise it must be a derv, and so my whittering on about the two oil pressure wires is wrong, ignore me.

there should be the big thick red, possibly a slightly thinner red on the main connection, a blue on a spade or bolt and another wire, which will be for your rev sensor, or/and rev counter on "W"

[Ginothy]

Aaah I see. I bought it with a '97 Golf 1.9 Tdi in it.

Big thick red wire, check, connected. Thin blue wire with ring terminal, check, not connected. Thin red & black wire, check, connected.


P.S. Applogies for not mentioning the engine that's in there in the first place.

[Mocki]

that blue should be the charge light (battery) on the dash.

[ghost123uk]

that blue should be the charge light (battery) on the dash.

So, (just in case Tim didn't figure it) with the blue wire NOT connected, your dashboard charging light should NOT be working correctly...

Or is the problem elsewhere? i.e. actually a problem with the oil pressure? (starting to understand why it's called the BOD).

As this happened suddenly, just after you worked on the alternator, this is unlikely to be anything more serious than a simple wiring problem.

[Mocki]

ok, you may have seen this, but maybe you didnt.

from the Wiki

The low/low pressure warning operates from the low-pressure switch on the engine. On diesels this is mounted on the forward-facing end of the head; on petrols it is mounted under the LH cylinder head.
The high/low pressure warning operates from the high-pressure switch. On diesel this switch is mounted on the top of the oil filter housing; on petrols it is mounted near the water pump housing (quite a confined space for access)
The low-low pressure switch information is used up to ~ 2250 rpm. At this point the electronics in the PCB switch to the high-low pressure switch. This sensor switch is present in later vans whether there is a rev-counter fitted or not. It is also common to other VWs of this era.
The flashing oil pressure light is operated alone by the high-low pressure switch and hence at engine speeds of over 2000~2250 rpm.
The flashing oil pressure light and 'buzzer of doom' are operated by the low-low pressure switch, hence at lower engine speeds.
These two conditions have both been observed in diesel-powered T25s,

[ghost123uk]

Hi Steve, I wonder if that entry would benefit from a bit of info re how the system monitors the ~2000 RPM break point, (wire colours and locations) for the high pressure BOD.

[Mocki]

yes, im sure it would, feel free.
i cant remember the wiring colours its years since i played with one.
however as the problem is pretty surely in the engine bay of a modded van, wire colours may well be pointless on this thread.... i dont know, i have little diesel knowledge, and none of alternative derv engine transplants.