SLROC Forum

So, I'm a tad puzzled by this one. Its happened 3 times so far. Engine running OK, come to a stop, turn off ignition, remove key....engine still runs.....disconnect battery...still running, open bonnet and pull plug on the coil - stops ! Most of the time it all behaves quite normally, turns off on the key etc.

The story is that its an ex 24v Lightweight that the last owner did a home conversion to 12v on. No, theres not a second battery anywhere. The other part of the story is that if the ( new) battery is not disconnected it flattens in 36-48 hours.

I've no idea where to even begin - how on earth would a petrol engine carry on running with the battery out of the loop - some sort of feed direct from the alternator I suppose ?

Ideas ?   

Any basic petrol engine will not require a battery. That's basic as in it has points and not multiple ECUs The alternator will be fine for a spark. Competition battery cut outs have a main part to disconnect the big battery cable and a wee switch on the back for the LT circuit.

If the battery goes flat then it may be because the ignition switch is not disconnecting the ignition properly. Is the coil warm a couple of hours after stopping the engine?
But to try and isolate the problem..............
Disconnect everything remove ............. all fuses and the wires from the back of the alternator then put a multimeter across the battery .......... it should be about 13v ..... then reconnect things one at a time and if you're lucky at some point there will be a drop in voltage as you connect the faulty circuit. If this is when you connect the alternator then its rectifier is probably away. Being a home conversion the fault could be anywhere .......... a frayed wire that occasionally rubs is another possibility.

If you have to manually stop the engine the pull off an LT (low tension) wire from the coil rather than the HT  (king lead).

Don't want to overdo the health and safety, but I'd be tempted not to leave it with the battery connected until the fault is isolated.

Best of luck.

Sounds like the bodged wiring has given the ignition system a permanent feed.  This would explain the running on and the flat battery and yes the engine will run on with the battery disconnected, the alternator will simply power the engine.  Try a simple test, with the ignition switched off and the engine not running use a test lamp or a meter to see if there is still 12 volts getting to the coil ( you need to disconnect the lead on the coil thats not going to the distributor and see if the lead has 12 volts present).

If it has 12 volts then the ignition system is not being switched by the ignition switch.

ZD

Thanks, I'd not realised that the bty could be out of the system like that. A couple of good leads for tomorrow evening then...

Cheers,

G.

genem, I'm guessing yours probably doesn't have them anymore, but my lightweight kept flattening its battery becasue of a short to earth inside the infra-red headlight relay. (it doesn't have the IR headlights but still has the relay). The relays are notorious for failing in this way. Mounted in the engine bay on the bulkhead - passenger side. I pulled the feed off the relay and problem fixed. Either way, you definitely have a short to earth in the wiring somewhere if its flattening the battery.

I've not had time today to do any more checking but thanks for the leads. The last owner basically hand-made the loom in HD red cable, all nicely labelled up...but a Ferrero Rocher box lid as a cover on the fuses .... etc etc.

I think I might end up taking it all out and replacing it with an Autosparks ready built job.

G.

I think I might end up taking it all out and replacing it with an Autosparks ready built job.

G.

That's not the Land Rover Owner spirit Gene!

That's not the Land Rover Owner spirit Gene!

 

Have anti-diesel solenoid valve ?   late Zenith 36iv and Weber do   

I may have this wrong, but this is worth a try / thought.

It sounds as if the alternator is still being fed with 12v to the rotor when the ignition is switched off, and the feed to the coil is on the same switched circuit.

I would suggest that you check which switched supply is feeding the alternator
Check which switched supply is feeding the coil.

the easy way to check if you don't have a multimeter is get a 12v light bulb, solder a lead off the central pin, and connect the lead to your coil supply, if the coil is illuminated in the ignitions switch "off" position, someone has wired it to a perminant live feed.  [most likely... solution trace wiring and switch to the ignition "on" feed]

I would also suggest that you check the live supply to the alternator (not the large live supply!, the live supply to the rotor, small wire at the rear of the altinator] and do the same check, this supply should also be served off the lngntion "on" feed.

You battery may be being drained because the ignition coil and altenator rotor are being feed a live 12v feed when the engine is in the off position.

Would also suggest that you check the ignition switch its self as there may be a contact within it that is not opening.  Basically in the off position, you should only have one live contact on the switch, in the ignition "on" position, 2 contacts, and "start" position 3 connectors.   [you may have a 4th position, but this would be the same.