starting problem

Hi, I was recently doing some welding on my dads Range Rover classic, around the back tail and now it won't start, when the problem began it would turn over and over suggesting fuel or spark but now when I turn the key to start all I here is the starter motor kicking in and something instantly drains the battery from 15 volts to 7 volts and I'm left with the starter motor just clicking.
The battery on it is a deep cycle and seems to be good, as it keeps a charge and it also starts other cars, the only way to get it crank is to get a jump start from another car and then it just turns over and over, no hint of starting.

Its a 3.9 V8 efi, k reg (92), I have checked that it's getting fuel, spark, checked all fuses I can find and it also has had a new distributor cap.

My dad has owned it for nearly 3 years and since ownership it would always start up slowly, like winding it up really, but would always start so thought nothing of it.

Anyway, does anyone know what the problem is? and how do I check to see if a relays are working?.

Were you using an arc welder? If so did you disconnect the battery before you started?? If not, you may have fried anything electronic.
No battery should show 15 volts so summat is wrong, maybe your meter. What you need to know is the voltage when you turn the key, if it drops immediately to 7 volts it looks like the battery is shot.

No I was using a mig and it was grounded to the car, it might be the battery but I'll have to check this tomorrow or maybe later on, raining!.

Check the earths engine to chassis. Check starter and connections to it. If you did not have the battery disconnected when you did the welding you may have blown the alternator diodes. 15 volts is a bit much, what are you charging the battery with? If it's a good battery and it drops that quickly it is getting a serious load or it's knackered. Have you had it shunt tested it maybe duff.

Thought any kind of welding, Arc, Mig/Tig/Mag, stick, gas etc is best done without the battery connected regardless....

Saint.V8 said:

Thought any kind of welding, Arc, Mig/Tig/Mag, stick, gas etc is best done without the battery connected regardless....

Click to expand...

Arc covers MIG, TIG and plain old ARC in my book, I should have made it clearer. Farmer friend used a TIG welder on an implement on the back of his all electronic tractor without disconnecting the battery. The next time it moved was on the back of a low loader

I will try another battery and check all earth's from and to the engine, tomorrow.
Thanks for all your help.