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Hoping someone can advise on this - driving my classic today, 2 years after rebuild including complete rewire and has done 4,000 miles with no trouble. The car has a typical sixties oil-filled coil, distributor, points replaced with aftermarket module, new AGM battery, new leads everywhere etc. No ECUs or computers in sight.
Today, with no warning the engine stopped instantly, as if the key had been turned off, and the ignition warning light came on. I managed to pull over somewhere safe, turned the key off and back on and it fired up and I continued. 2-3 minutes later, it did it again. This time I had a look but couldn't see a problem. The king lead, HT from coil to centre of distributor cap, is not a great fit so I pulled it out and carefully refitted it properly. I then drove home, 120 miles, with no problem. However once going again, I noticed that the ammeter (yes, it's early sixties) was now showing +15A once the engine was above idle for the whole journey. If left to idle it dropped to -15A. Prior to the stopping incident, it pretty much stayed at zero all the time except for immediately after starting for a short while.
Can anyone suggest what I should check? The dynamo has been replaced by a Dynator, which is an alternator that looks like a dynamo. Do I now have a damaged alternator, or maybe a failed battery (Exide AGM, much less risk of corrosion to the battery mountings)? I'm pretty sure it shouldn't be showing 15A charge all the time I'm running above idle.
As you can tell, my knowledge of electrics is close to zero so any help would be very much appreciated!
Thanks,
Roger
 
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ruston

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You may of discharged an already low battery cranking to restart , it could take awhile to top up again depending on the output of the alternator and the power used due to the size of the engine. Other than that you may have a bad cell , unlikely as it seems every thing is newish. You may also have a bad earth that also may have contributed to the engine stopping in the first place.
Out of interest what kind of vehicle is it?
 

telectrix

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50181
without the flux capacitor, it's dead.
 
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You may of discharged an already low battery cranking to restart , it could take awhile to top up again depending on the output of the alternator and the power used due to the size of the engine. Other than that you may have a bad cell , unlikely as it seems every thing is newish. You may also have a bad earth that also may have contributed to the engine stopping in the first place.
Out of interest what kind of vehicle is it?
Thanks for the response - much appreciated. After the car stopped, I drove another 120 miles over 2.5 hrs to get home, so I would have thought it should have been topped up by the time I got home. No lights, wipers, stereos etc. on, just driving. It was still showing 15A discharge at idle and 15A charge at anything above about 1000rpm.
I wondered if the king lead coming out of the coil could affect either the alternator or the battery? Don't know much about AGMs.
The car is a '65 AC Cobra, original old American Ford V8, 4 barrel carb, Ford points distributor converted with a Pertronix module, and everything else as standard. Earthing is fine with everything new.
 

ruston

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Yes 120 miles would do it , I admit to missing that lol.
 
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Originally the car would have had a Lucas C40 dynamo and a Lucas RB106 bobbin regulator, but as it has the Dynator (a modern alternator hidden in a dynamo casing) it has no separate regulator. Whatever controls the charging is presumably internal in the alternator. As I mentioned, I'm no electrician but I wonder if the coil being powered by the LT side but unable to deliver HT due to the lead coming loose could have damaged the charging electronics in the alternator. Or the battery? I don't like coincidences and I think it's unlikely that the coil HT lead came adrift at the same time as either the alternator or the battery developed a fault. I've heard mixed reports of AGM batteries. Would it help if I measured the battery voltage at idle and at 2,000rpm to see if it's an alternator problem? Any point in connecting up a spare battery to see if that makes any difference?
 

telectrix

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it's a Cobra V8. as long as it growls who cares about the electrics?
 

Strima

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Check for loose connections on your charging circuit and wiring loom. Also a loose earth between chassis and engine can cause issues.
 
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Thanks, I'll have another go over it all. I'm mostly concerned that something's been damaged now and will need replacing. But where to start?
 
D

Deleted member 26818

Test the battery using a battery tester.
 

telectrix

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then check all connections, then voltmeter across battery when not running (should be 12V ish) then with engine running 2000rpm should get 14.2V
 
D

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Is there a particular type of tester for an AGM battery?
No.
All you are doing is placing a load across the battery and then checking to see if it recovers.
If the voltage doesn’t recover on a fully charged battery, then the battery will fail.
 
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OK, thanks. So, I'm assuming the ammeter should be showing zero (neither charge or discharge) most of the time, after it's had a chance to recover from starting the car. If it continues to show the system is charging for a long period of time, it's either a failed AGM battery or the alternator's internal regulator circuit has failed. Is that right? If the battery is tested and is fine, I need to look at the alternator.
Sorry, really not good with electrics!
 

ruston

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As long as you are sure you all the leads and earth's are secure and the battery is actually receiving the charge; as in @telectrix description , the ammeter would not show high amps at rest with no loads like air conditioning etc.
Do you have a battery to replace for a quick comparison .
Are the alternator drive belts tight , or is it having to work it's guts out.
To be honest it could be one of many things.
 
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  • #18
Yes, I have a decent used lead-acid battery I can connect up and see if that makes a difference. The belt system is simple - just one v-belt round crank pulley, water pump and alternator. No air con, p/s or anything else. The only item consuming power on today's drive was occasional running of an electric cooling fan, but as the drive after the engine stopped was all on motorway that didn't cut in.
 

ruston

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And the belt is running free ? No resistance from the water pump?
Try the battery , other than that it is a job for test equipment.
 
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Yes, no stiffness or resistance. I'll leave the lead-acid battery on a Ctek overnight and try tomorrow to see if the ammeter reads differently.
 

telectrix

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once had a problem with a datsun240, belt drive to alternator and power steering, bearing seized and belt slipping . battery kept going flat till i found the problem.
 
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AC Cobra? 120 miles in 2.5 hrs? You weren’t driving fast enough ;)
It was the M20, the M25 and the M11, with the crowning glory of the A14 after Cambridge just to finish off with. I'm amazed it didn't take 4hrs!
 

ruston

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I can remember when I was lad.. They used to speed test those on the new M1.
They were doing phenomenal speeds even then.
 

pirate

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I can't believe I'm the first one to ask for pictures!
We love pictures on here!
OK, I accept that in this case they won't help with diagnostics, but car-porn is always welcome!

On another point...my past experience suggests battery failure, usually caused by alternator fault. Ammeter should show charge for a few minutes after cranking, then settle near to zero...if the physical drivetrain is ok (belt/water pump/alternator) then battery or alternator is the problem.
 
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My pleasure. It's a '65 leafspring street car - no bulges or stripes here, I'm afraid - also only the 4.7, not the 7 litre.IMG_5363.jpg
 

pirate

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That is a thing of beauty...and I do not mean your immaculate paved driveway!
Thank you for sharing that ...
 
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Also - a quick pic of the offending items:
 

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