Diagnose this!
Discussion
Here's a strange one- couple of weeks ago I started my Cerb after it lying up for a few days and drove 100 miles.
Parked for an hour, when I came back it wouldn't start, it was behaving as if the battery was flat. Called the AA, they jump started it no prob.
I then drove to a hotel, left it overnight, and in the morning, yep - battery nearly flat. I got a start from the hotel who had one of those jump start gadgets - the engine spun perfectly with it.
Then I drove 100 miles home. Left the car 2 days, started it fine. Wha?
I suspected the alternator, so I gave the car to my local indie mechanic, a very good guy, who took the alternator out and had it tested - results nothing wrong!*
The battery is quite new, about 2 months.
Can anyone help me diagnose this?
* by the way, it was the first time my mechanic had taken the alternator out of a Cerbera. He told me today that whatever stupid idiot designed it so the alternator was THERE deserves to be shot with pellets of his own sh*t !!
Thanks
A.
Parked for an hour, when I came back it wouldn't start, it was behaving as if the battery was flat. Called the AA, they jump started it no prob.
I then drove to a hotel, left it overnight, and in the morning, yep - battery nearly flat. I got a start from the hotel who had one of those jump start gadgets - the engine spun perfectly with it.
Then I drove 100 miles home. Left the car 2 days, started it fine. Wha?
I suspected the alternator, so I gave the car to my local indie mechanic, a very good guy, who took the alternator out and had it tested - results nothing wrong!*
The battery is quite new, about 2 months.
Can anyone help me diagnose this?
* by the way, it was the first time my mechanic had taken the alternator out of a Cerbera. He told me today that whatever stupid idiot designed it so the alternator was THERE deserves to be shot with pellets of his own sh*t !!
Thanks
A.
Maybe a dead battery, maybe the pesky 100A fuse has blown, maybe something else. I'd expect the AA man to check the voltage at the battery (as well as at the alternator) to confirm it was charging OK. Anyone with a voltmeter should be able to do this in 30 seconds. If it was, and if it really was going flat that quickly, either you have a hefty electrical leak or a dead battery.
Sounds like it's not charging properly, or is doing so intermittently. I had a vaguely similar problem whereby the battery would go flat seemingly at random, sometimes after a couple of days of inactivity. I also went through three 100amp alt fuses over 12 months. The problem was bad contact at the fuse which gave poor charging and generated a lot of heat which would occasionally melt the fuse (it always blew at the driver's side end of the fuse, dunno if this is significant). Test the voltage at each end of the fuse with the engine idling, should be the same at each end (13.8v or so).
Another symptom I had was that the Optimate would take several hours to go green after a run. When the fuse blew again I sanded down the 'O' ring connectors that the fuse sits on to remove the rust/corrosion, sprayed some wd40 on it and tightened up the 8mm nuts nice and tight. Now the optimate goes green after a couple of minutes even after I've been driving with lights/wipers/stereo etc, and no more starting problems. Highly recommend cleaning those contacts.
Poor charging can also ruin the battery so you might need a new one once the charging problem is sorted. Or you might just need a new one anyway.
Another symptom I had was that the Optimate would take several hours to go green after a run. When the fuse blew again I sanded down the 'O' ring connectors that the fuse sits on to remove the rust/corrosion, sprayed some wd40 on it and tightened up the 8mm nuts nice and tight. Now the optimate goes green after a couple of minutes even after I've been driving with lights/wipers/stereo etc, and no more starting problems. Highly recommend cleaning those contacts.
Poor charging can also ruin the battery so you might need a new one once the charging problem is sorted. Or you might just need a new one anyway.
Julian64 said:
I don't have much to offer you in diagnosis, but can I ask why a motor mechanic would possible want to take the alternator out to test it when you can do that in the car without touching it?
Because you can't test the alternator for supply current capability, without putting it on a test jig, you can't check the diode pack is OK and you can't inspect the brushes and commutator when its in the car.
A.
i know it sounds unlikey but i have had duff batteries in the past you think to yourself i,ll check other components because it cannot be the battery and low and behold after hours of checking various bits back to the battery and thats the culprit.your local spares shop should be able to put there tester on it to confirm / eliminate it, alsop like the other guys have said could be the 100 amp fuse anyway good hunting
You're right, it's easy to assume a battery is OK because its new - whereas it could be duff.
I'll check it - thanks.
Andy.
I'll check it - thanks.
Andy.
ancol said:
i know it sounds unlikey but i have had duff batteries in the past you think to yourself i,ll check other components because it cannot be the battery and low and behold after hours of checking various bits back to the battery and thats the culprit.your local spares shop should be able to put there tester on it to confirm / eliminate it, alsop like the other guys have said could be the 100 amp fuse anyway good hunting
I've heard about a very similar problem to this, and it turned out that the alternator itself had a faulty diode. It's very difficult to diagnose because everything appears to check out. When the engine is cold, check if the alternator feels warm, if it is then it has a faulty diode.
jensena said:
I've heard about a very similar problem to this, and it turned out that the alternator itself had a faulty diode. It's very difficult to diagnose because everything appears to check out. When the engine is cold, check if the alternator feels warm, if it is then it has a faulty diode.
Well you're right, if a diode in the rectifier goes short circuit, it will allow current to flow the wrong way and drain the battery.
I wondered about that, but the thing is that if I charge the battery with a charger then don't drive the car, the battery holds its charge, so I discounted that.
Also I assume - assume - that the guy who checked the alternator checked the diode pack. I'll ask though!
Cheers
Andy.
Immobiliser?
It bugged the shite out of me while I was trying to figure out what was actually wrong with mine.
It behaves in all sort of wierd ways that point to something else.
Might be worth giving a shake to the loom going into the immobiliser the next time it happens just to see if it starts when you shake it.
Worth a try.
It bugged the shite out of me while I was trying to figure out what was actually wrong with mine.
It behaves in all sort of wierd ways that point to something else.
Might be worth giving a shake to the loom going into the immobiliser the next time it happens just to see if it starts when you shake it.
Worth a try.
Cos its pointless. The holder broke once, so I bypassed it. Then someone explained to me what it did (its between the alternator and the starter/battery) so its largely pointless.
copilot said:
Why no big fuse? If you had one at least you'd be able to check it! Why has it been bypassed?
Edited by alinton on Monday 30th April 22:31
Hi !
It could be something much easier than the alternator or the battery.
Check if the light in the boot works properly, if it stays on for a night or two you will drain a battery that isn´t fully charged, the switch that turns the light on and off could be working intermittent.
It takes about one to two hours to fully recharge a drained battery with the alternator in the car.
Peppe
It could be something much easier than the alternator or the battery.
Check if the light in the boot works properly, if it stays on for a night or two you will drain a battery that isn´t fully charged, the switch that turns the light on and off could be working intermittent.
It takes about one to two hours to fully recharge a drained battery with the alternator in the car.
Peppe
alinton said:
Julian64 said:
I don't have much to offer you in diagnosis, but can I ask why a motor mechanic would possible want to take the alternator out to test it when you can do that in the car without touching it?
Because you can't test the alternator for supply current capability, without putting it on a test jig, you can't check the diode pack is OK and you can't inspect the brushes and commutator when its in the car.
A.
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