A question about alternators

[genphreak]

Hey everyone,

Been working on the neighbour's M20 powered E30 (325i) today. We changed the timing belt, tensioner, belts and buttoned it up again. All that happened out of the normal was we managed to break the speed sensor off the No.6 wire. I soldered it back on, reinforced the connection from subsequent breakage. Once connected she runs fine- no problems... except for the battery light coming on.

It seems to be a strange problem and I can't work it out.

So I've been searching everywhere to no avail. Tthe trouble other people talk about tends to be about the exact opposite;

i.e. " I get a glowing charge light at idle, which gradually goes out as rpms go up..."

The problem that is happening to ours is that the charge light is gradually coming on whenever the revs are higher than idle.

Would anyone know why this could be happening? All he did in the meantime was charge the battery as it had not been charged for a while. There is no OBC to check voltage but my meter reads 13.12-13.14V across the battery no matter what the engine speed is. Need to check it against having the lights on (didn't get that far before he had to go do an errand).

Surely this is not a faulting regulator/alternator, choosing to go wrong at the same time as we do the timing belt!

Many TIA, Nick

[acidfire52]

Sounds a little low to me. Mine idles at about 13.7-13.9
Might the the regulator.

[Kalevera]

If the car is actually not charging....Do a voltage drop test across the alternator casing to the engine and then the engine to the chassis (or just the alternator to the chassis). In the process of changing the timing belt, the alternator position adjustment bracket was removed from the front timing cover. The alternator is isolated from the engine without that bracket in place -- it grounds the alternator to the engine. If it's not getting a good contact, the battery light would go on.

[genphreak]

Thanks for the replies fellows.

Just tested it;

At idle the battery runs at 13.3V unloaded
Lights on=12.9V
High beams=11.9V

Revving it up a bit helps- but 13.8V is not attainable. Since that proves we are getting some charge but not enough, we reckon the belt is slipping. Off we go to get a new one tomorrow.

Interestingly, the alternator bracket seems to work better (from a geometric point of view) on the Power Steering pulley and the PS bracket works better on the alternator... so long as you use a slightly longer alternator belt in this configuration- the stock one is fine but you can do with one that is 970 or 975mm. It was pretty hard going getting the old (stock) 965x95mm stretched one to go on

We tried it both ways to work it out: With the stock belt and the stock bracket we couldn't get it tight which is what led us to think we'd mixed the brackets up so we then tried it (what turned out to be) the wrong way round. As I said, it turns out to be an improvement on this car.

Obviosuly we need to replace the old'n'shitty stretched belt now. We stretched it some more, but the ECU chip we got with the MAF kit went in at the same time (and turned out to be dead) so we're yet to see if the charge light turns off. The car won't start with the Rom they sent us. (but that's another story)...
thx for the thoughts.. I'll let y'all know if it turns out OK or not nick