Phantom current draw-OD solenoid/dead battery

[AlexO]

Chaps,

Small technical issue. Having upgraded my altnerator to an (albeit used) 100A 940 model I seemed to have solved my battery charging issues and run in to some new ones.

I drove ~250 miles on Sunday without an issue from the car. Drove the car on monday for maybe half an hour with, again, no issue. Went to start the car this morning and it started but very reluctantly with a low reading on the dash voltmetre (aftermarket, connected across that fuse you connect a voltmetre to). Went to nip out of work at lunch time and had everything electrical happening to start the car except the car actually starting with audible click from the starter relay and ~10V on the metre. I managed to get a jump start but noticed the OD light was on and wouldnt respond to the button on the gear stick. I checked the fuse and it basically crumbled in my hands but obviously thats the one fuse I don't have a spare for. I drove the short hop home with ~14V on the metre and the car seemind fine.

I assumed it was a dodgy current draw from the solenoid circuit not disengaging so parked at home and disconnected the battery positive terminal that still had ~13V on the voltmetre when I parked. Went back to the car, reconnected the battery, it showed ~10V and wouldn't start.

Possibilities:
1) Battery is dead for unknown reasons even through it's not old at all, nothing to do with the overdrive
2) Overdrive circuit wasn't disengaging, draining the battery, my jump start was enough to get the car going but since I didn't drive for long the battery didn't get enough charge to start the car again and the ~13V when I parked the car was just the nedle sticking
3) A combination of both or a completely different current draw (potentially central locking) draining the battery

I'll charge the battery at home and get a replacement fuse and hope that fixes it, otherwise I need to start hunting bad earths and dodgy electrics (YAWN). Any thoughts and feelings on where to go with this or where to start are greatly appreciated.

Cheers

Alex

[AlexO]

Another point that's just occurred to me: The red small red spade-connected cable on the back of the alternator looks excessively worn. Does this relate to the self-exciter or is it just the alternator warning light wire? If the alternator isn't self exciting due to low revs on short journeys it might not be charging the battery.

[AlexO]

Small update even though there's been no input on here.

I went through my fuse box on wednesday night and pulled the fuses one by one whilst the old man had an ammetre in series with the battery with the ignition turned off. Fuse eight (door locks, clock etc) was pulling a few milliamps but fuse six (fuel pump etc.) was pulling a lot of current. Like, a LOT of current. Enough to give a small arc between the fuse and the holder when I was pulling the fuse.

I tried pulling the fuel pump relay but it didn't make a difference to the current draw. I'll replace this relay and hope it solves the issue but if anyone else has got any ideas I'd be grateful.

Even with a fully charged battery and the sound of an engaging fuel pump the car wouldnt turn over this morning. Would a busted fuel pump relay cause this? EDIT: I replaced both fuel pumps about this time last year.

Thanks

Alex

[Derek UK]

If your OD switch is in the gear knob, the wiring for this can break down or get displaced etc., maybe causing a short. Remove centre console to check it out.

[Stephen Edwin]

The comment about the overdrive switch rings a bell from a previous thread.

It is a tad odd that the current drain occurs immediately after changing the alternator. But it's hard to see a cause and effect and coincidences do happen. The battery [possibly] draining while disconnected is a worry. I hope it wasn't really fully charged. Some cogitations, possibly not [all] related:

• Is the 940 alternator suitable for a 240? For example perhaps the 940 also has that odd live contact on the alternator issue, or perhaps they are rather different animals? Either way, is the alternator connected to the car correctly?
  
• What is the conclusion re the battery? If you charge it fully off the car and keep it off the car, does it discharge? Is it sealed or can you check individual cells with a hydrometer? Can you get it checked by an auto electrician? I understand they have interesting test equipment nowadays.
  
• How many circuits are fed by your fuse 6? It's a game of isolating circuits and tracing the fault. A test light is your best friend.

Good luck. I hope it will be something small and hopefully cheap.

.

[BrianH]

Its worth checking the earth connection from the alternater.

The whole thing is isolated with rubber bushes.

I had mine rebuilt but it still gave trouble. Took it back it was retested and I could see there was no trouble with the rebuild.

He said it was the earth...............and yes I have had no trouble since.

Watch the large rubber bush at the front of the engine that supports the ajuster arm. If that becomes worn the adjuster arm is likely shear. Took me some time to figure out why the arm was shearing, even the welded ones. The bush solved that problem.

Get Bosch brushes they last 3 times as long.

BrianH 27 milesto 640k. Most on LPG. 1989 GL

[AlexO]

Chaps,

Thanks very much for the input.

BrianH that's an incredibly good point. The 100A alternator is a much bigger unit than the original 240 55A version so sits a lot closer to the engine. If this is earthing somewhere on the block, or the earth went funky after the intervening day's driving after fitting, then this could well be the problem.

I had a good chat with my brother and he highlighted the fact that the problem's probably not in the fuel pump relay since removing the relay doesn't remove the current drain. If there's a lot of current through that circuit with the ignition turned off it does point to some kind of short in that circuit (obvs) so I'll have to go back to our old friend the wiring diagram. Sigh. Overdrive problem was fixed with a new fuse though so that's a plus.

More updates as I find new things. Thanks guys!

Alex

[Derek UK]

Does the alternator wiring run under the front of the engine on your car? It can suffer from oil and physical damage at this point if it does. The fact that you have been pulling the alternator harness around might be a pointer. Ensure that the alternator is properly earthed to the block.

[AlexO]

Chaps,

I left the car last night locked, with all fuses in. The battery was obviously depleted this morning but not enough to stop the car starting and running. I checked the alternator wiring last night and all seems OK, I can't see any obvious places for shorts to the block etc.

I read somewhere that this is a classic "fuse six problem". Does anyone know anything about this? My fuse six does get very hot (as per normal) but I can't find any recommended method to diagnose an extreme current drain through it. Any ideas? The wiring diagram shows fuse six as sitting between ECU and EZK but I'm not 100%sure of it's function. I'll also start looking at door lock solenoids.

Cheers

Alex

[360beast]

If the battery has gone flat disconnected like you said it sounds like a dead cell to me.

I would start with a new/known good used battery and see if the problem still occurs.