Discovery 1 Help after jump starting

Hi Guys!

was being a good Samaritan earlier and giving a guy from works BMW 530D a jump start as he had left his headlights on. connected up jump leads (yes i did them right way) and he went to start it and nothing so though id try giving mine a few revs ago, as he turned the key i noticed that the rev counter went crazy and my engine started to splutter. so couldn't get his started so gave up and parked my disco back up. after work went to go home it started no problem, on the way home noticed that the speedo went crazy briefly then went back to normal. just been out to pick my mother up and it wouldn't start, could barley manage a 8th of a turn so got under and checked starter as I've had a few problems with that but not that. called a mate over to give me a jump start. it started up but not willingly.

had to drive home with no lights on, as the engine had no power with anything on even the hazard made it lurge. on the way back i had no rev counter and no speedo and the SRS and ABS light on the dash.

so my worry is, if his car had an electrical problem could it have cause a short or wire to melt etc in mine? any ideas on where i should start to look, I'm going to investigate further in the morning.

sorry for the essay!

Its a discovery 1 v8i 1997

Sounds like you've fried the battery or Alternator. Have you checked em with a multimeter??

thats going to be my first port of call today. Will report back

Not sure about V8 but Speedo on tdi gets its reading from the alternator, not sure if its mechanical or electrical tacho though but I have known alternators with failing bearings that give crazy readings to the Speedo still give good enough power for years. I have a feeling that the dead beemers battery put too much load on your alt or batt, did you try to let his Bart charge up from yours first or did you try to start the BMW directly from your battery? Is the BMW diesel or petrol? Are your jump leads heavy duty recovery type or normal service station quality? Did you connect the negative lead to an earth on his car or direct to the battery negative terminal? The usual situation is that you try to jump start someone with normal leads (which are only capable of starting a small petrol engine or charging but not starting a big or diesel engine) they keep trying to start their engine without letting their battery charge (or their batt is totally f%#£&?d) which puts a huge amount of load on your system, so if you remember a lot of failed starts and clicking from his starter solenoid then chances are you've killed your alternator or battery. Check alternator output, if its low check belt, tensioner and idler before replacing. Give battery a full 24 hours charge on a smart charger as alternators never really fully charge a battery back up. For future jump starts always use heavy duty cables, always go direct to the battery negative and always try to charge the other battery for at least 10 minutes, if its a diesel you may want to remove the fuse for the glow plugs after they've been used once or twice) if their battery is suspect then loosen their negative terminal, attach your jump lead, slide terminal off battery, start vehicle (this way its direct from yours without the huge power drain of a dead battery) THEN slide terminal back on battery and remove your clamp. That way their knackered battery will only damage their alternator not yours.

Obviously don't do anything I said about touching live cables while starting a vehicle, *yawn* live wire.....gloves....elf n safety......leave to professionals....dont try at home....blah blah blah

But seriously, common sense is needed.

They where heavy duty cables and was a 3Litre doozle and connected straight to battery let it charge for a few mins, but you could hear his starter solenoid clicking, i think from the sounds of it, gotta be my alternator. Havent had a chance to look yet will investigate tomorrow morning most likely

'Not sure about V8 but Speedo on tdi gets its reading from the alternator'

Think you'll find that tachometer is taken from alternator and speedo is taken from transfer box transducer, check cable from alternator to starter ( charge lead ) and also check engine to body earth, hope this helps

Speedo driven off cable on early ones and later ones are pickup.

tacho driven off alternator

just on the jump start think i bet you put both your jup leads on the BMW battery right? if so then you've defiantly burnt your alternator out, want to know why?

I waz thinking same thi g with bmw being on the wrong way round

remedave said:

just on the jump start think i bet you put both your jup leads on the BMW battery right? if so then you've defiantly burnt your alternator out, want to know why?

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Yeah...

remedave said:

you've defiantly burnt your alternator out, want to know why?

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Go on then...

Whoops sorry for got about it,

Well What i think you've probably done (i can't say for certain as i wasn't there) is double Positive you can only partially see the battery on the BMW right those 2 terminals are both positives, hence the it made no difference to the BMW when you connected it to your disco, and you've given your disco a right old shock and burnt the regulator out.

I might be wrong as i say but i have seen it done many many times particularly with citroens and Peugeots, for must use the designated chassis earth not the battery terminals theses days as the more and more advanced vehicles are becoming the more power they need most vehicles have split power cells these days and multiple terminals, my advice is if you're not sure don't jump it !! and if you do jump it make sure you turn the headlights on both vehicles and keep them connect for around 5 - 10 mins after the jump start as you can spike the ECU's and ruin them.

Oh and if it wasn't that i will throw this in the mix too, These days Black can be positive and green and yellow !!! so be careful left connected wrong to long you'll go bang.

fanatic said:

Speedo driven off cable on early ones and later ones are pickup.

tacho driven off alternator

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The v8s I've had in classic Range rovers had tachometer transducer in front of bellhousing

When you connected the jump leads on your car, you didn't loosen the terminals slightly without noticing did you? Seen that happen a few times where people haven't pushed the clamp down and tightened them correctly, works for ages until they're disturbed.