Electrical minded anyone?

[45_CB]

A friends Cupra seems to have developed a strange problem since a cold day recently.

It will only start with jump leads connected from a donor car, but the battery has been charged and is holding 11-12v's and we have also tryed another spare battery too. When the car is running it is charging at around 13-14v's and drives fine.

Without the jump leads from a donor car, when the ignition is turned on everything is dim and when you go to start it there is no power like a flat battery.

Cant seem to work it out, anyone suffered the same issue?


Thanks in advance for your reply

 

[harty190486]

sound to me like you have an earthing problem check main car negitive from batt to shell is clean and clear of rust check all ground points where neg is connected to

 

[techie]

Agreed, connect the jump lead from a suitable bracket on the engine to a chassis earth and try it.

 

[45_CB]

use one jump lead from a donor car's battery earth work?

its strange as he's been using it for ages and then yesterday came out to dead battery

 

[45_CB]

just got him to try earthing off another car and any earthing points in the engine and places like the door latch and made no difference

 

[Slimy]

To me that sounds like a dead battery. You've done the right thing to test the voltage, and 11-12 volts off and 13-14 volts running may sound ok, but I bet there's no current behind those volts.

Get the car to Halfords or somewhere and get them to put their battery tester on it. It creates a load on the battery and properly tests it. I reckon your battery is holding enough voltage to run the multimeter but nowhere near enough to start the car. The alternator is working fine because of the increase in voltage. And everything else on the car is fine because it can be jump started.

If it had been a bad earth, and you were connecting the jump leads to the battery terminals, you still wouldn't have been able to start the car.

 

[45_CB]

this sounds good

Perhaps him using two potentially duff batterys could be the problem lol. Brand new battery time I guess or i'll take my battery round and try that maybe.

Ruled out the alternator I think as drives fine with everything working and voltage changes and he has no battery light on inside the car.

Thanks slimy.

 

[wild willy]

To me that sounds like a dead battery. You've done the right thing to test the voltage, and 11-12 volts off and 13-14 volts running may sound ok, but I bet there's no current behind those volts.

Get the car to Halfords or somewhere and get them to put their battery tester on it. It creates a load on the battery and properly tests it. I reckon your battery is holding enough voltage to run the multimeter but nowhere near enough to start the car. The alternator is working fine because of the increase in voltage. And everything else on the car is fine because it can be jump started.

If it had been a bad earth, and you were connecting the jump leads to the battery terminals, you still wouldn't have been able to start the car.

Correct, a flat battery will still display 11 -12v when unloaded. When a load is applied it will drop considerably or to nothing. A new battery will sort this.

 

[45_CB]

Thanks for your help, will let you know if it works!

 

[45_CB]

he just txted me and said the new battery today solved it!

sounded alot worse the way he made it out lol, forgot to say this was a MK2 Cupra

 

[Slimy]

Nice one!

 

[45_CB]

Case closed