Replacing the Alternator

[gerodan]

Hi, this is my first question because this is my first problem.

I've had my 450SE for about two months now and its first major problem is that it is killing batteries. It seems that the alternator is only charging the battery every so often.

Let me explain. It all started a week or so ago when I was sitting in the car waiting to meet someone. I was listening to the radio when it just died out altogether. I figured the battery had gone flat, but 10 minutes later when the person I was waiting for had arrived I tried starting it and it fired up fine. We drove across the city (only about 5km). We hopped out for 5 minutes but when we got back in it wouldn't start. The people we visited had jumped leads, so we started the car and drove around some more. I didn't stop the car in case it wouldn't start. The next morning it started fine. I drove to work and all that. Spent all day at work, then headed home. Again, it started fine. Halfway home it started running rough at idle. It was as though there was only spark on every second cylinder. I was stuck in traffic and found that if I put it in neutral while waiting at traffic lights then it would keep running, however this trick didn't work when I was in stop/start traffic on the ramp up to the Anzac Bridge. I couldn't get into neutral quickly enough so, with no spark, the engine stalled. I couldn't start it again.

So, hoping that the battery was just getting old, I replaced it with another one from another car which I knew to work fine as it was fairly new. It only took two days for this one to die in the Merc.

SO. What I know is that the battery is not being charged. I have experimented with the situation by starting the car with a charged battery and then disconnecting it in the hope of proving whether or not the alternator is faulty. Well. I'm not sure. See, when the battery is disconnected it runs rough but with enough throttle in neutral it will run with no battery. Obviously however the net charging output of the alternator is a negative figure because I've flattened two batteries in four days.

My question now is, where should I look at getting a new alternator from, or is there a likely problem/common fix which I may not be aware of.

All help appreciated.

Gerodan.

 

[s class]

It could be your alternator, but it sounds also like you may have an earth problem. There should be a thick copper braid connecting one of the lower bellhousing bolts to the chassis. CHeck that this hasn't frayed or corroded off.

 

[gerodan]

Should also mention, that for the time that the second battery was in the car it ran fine. The running rough only happened at idle with a dead battery, or when testing without a battery.

I will check the earth wire when I get home. From memory the negative battery cable comes straight off the chassis...though I'll have to double check. I changed batteries around in 3 cars repeatedly so my photographic engine bay memory is a little muddled at the moment.

 

[Michel]

It could be your alternator, but it sounds also like you may have an earth problem. There should be a thick copper braid connecting one of the lower bellhousing bolts to the chassis. CHeck that this hasn't frayed or corroded off.

Alternatively get an electrician to check the alternator for charging

 

[GreaseMonkey]

Yes there will be a cable from neg on the battery to the frame, but because engine mounts are rubber, there should be another from the frame to the engine block.
These can fray, but what is harder to detect. is that individual strands break down within the braided strap, but only let go when hot, so, it may start cold, but not when hot.
This is a common and hard to trace fault, try driving for a few days with a jump lead attached from battery neg to the engine block, this will have to be somewhere away from fans and belts, and also somewhere it can't get shaken off.
Or change the earth strap.
If that does not fix it, get your alternator tested.
It should show 13 or 14 volts, but in some cases where they break down, they will be actively discharging the battery.
If there is a charging fault, you should be getting the red light glowing on the dash though.
Let us know how you go,
Chris M.

 

[Styria]

Hi Gerodan, is there any chance of getting an update on the problem you had/have ? .....has it been fixed and, if so, what was the problem. Hoping to hear from you. Regards Styria

 

[Bandolero]

Sometimes the alternator light will not come on even though the alternator is not charging properly.
My auto electician told me this after my car had a flat battery because the alternator stuffed up, but the light never came on.

 

[BAR]

If you are a member, call the NRMA. hey can check out the operation of the alternator: if it's working properly and also the battery and battery condition.

Or else try the NRMA mobile service starter motor and alternator replacement service
ph: 1300 762 010

No more guess work and wasted money on fixing / replacing the wrong thing.

By the way, I once had a faulty starter motor, that when the car was cold / cool it would start. If the car was warm / hot - well dead as a dodo and one would have thought that it was the battery!