bfellows

All pointers appreciated on this one.

My car and bikes often stand for a month or two at a time so i invested in an Optimate trickle charge / conditioner. All was well for a couple of years and then the battery on the 928 went to deep discharge even though the charger was connected. First thought was duff battery as it was of unknown vintage - changed it, same probem occured.

Next, new trickle charger - all well for a while, but today trickle charger shows desulphate, then red triangle for battery problem. I've pulled the battery and tested it and it's good (only showing 12.7v though) , also with the battery removed from the car the Optimate seems to be charging / conditioning as it should (I have confirmed its operation on my bike and spare car battery - charges to 13.2v) This problem is the same as the earlier symptoms when my first battery went to deep discharge.

I can only assume that something is drawing current? I disconnected the CD multi changer and all interior lights are are off. The only other accessories are the clock and a Clifford alarm system that is set to sleep mode. (has been installed for over 3 years so predates most of the problems). Car shows charging at 14v when running, so I have discounted alternator.

Any ideas? How would I check for current loss?

Dean_Fuller

My 89 models PO mounted a disconnect switch on the rear tool cover. Its very handy for working on the car...just flip the switch and the battery is disconnected. When I spoke to him about it he had the same problem....didn't drive it enough and when he wanted to ...dead bat. If the car is charging while running okay, this would fix the problem with very little trouble.

the flyin' scotsman

I've the same issue Bert; a new battery lasts for a few years (driving seasons) before it goes into having problems keeping a charge when the car hasn't been run for a few weeks. The batteries are well maintained during the off season and when the car is running all indications are good.

My car, other than a modern radio/cd player, is electrically stock. Next tool to buy is current meter.

EC928NC

My 85 5-spd had a battery draw problem too... My car sat for a couple months while I did my TB/WP r&r and when finished, fired right up. After a few weeks of driving I had symptoms of a low battery... hard, slow starter engage, jumps.

I found that the driver's door switch wasn't always grounding. The power window realys use the door switch for a de-energise ground point. When the switch didn't ground, window regulators stayed hot. I had to remind myself to make sure the dome light lit whenever I shut the car down and got out.

Yours may have a similar issue.

Alan

Simplest method (to start) insert a DMM/ammeter on 10A range into battery ground strap circuit - DMM +ve to the ground point and -ve/com to the battery -ve post. what current do you get ? - ensure the interior lights go off (pull connector at bottom under hatch receiver - what do you get now? if its below 0.2A switch to 200mA range...

Now permanently disable the interior lights - pull the fuse... (disconnect DMM before you open a door!)

Remove fuses 1 by one across the panel first individually (note current reading remove fuse, note down current reading, replace fuse, note down current reading (was it the same as when you started?)

If any of these fuses when removed gets you down to <30mA I think you can consider you have found the culprit - ideally it would be <20mA but 30mA will not be a major problem. You still have work to do but its narrowed down substantially...

If it doesn't - make a list of all your fuses and their values - or check the installed fuses against the printed list or 928gt.com list or take good photos of your panel for later reference...

Start removing fuses from the middle of the panel (these are where the directly battery supplied fuses are) out to the sides . Note the value before you remove as before, remove the fuse, then note the value again - do not replace the fuse and keep going until you have removed all of them - how low do you get now - if still not below 30mA its leakage on a non-fused feeder - unfortunately there are many.

In this case here are some possibilities - the most likely culprits:

Unplug the ECU's - any difference

Unplug the "Xbus" or "supply" relay

Unplug the rear defroster relay

Disconnect all wires at the large connector on the alternator (big red wire) then bolt them bacl together but not attached to the alternator - do this with the battery disconnected - then reconnect to test - repeat test with all the wires completely seperated...

Unplug the cooling fan driver stage (plug at the very front to the finned black unit)

Unplug the cooling fan control unit (under sill cover near amp)

Disconnect the large red ABS feeder (from the starter)

Alan

the flyin' scotsman

Good thought Brad; I check to ensure the interior lights go out but as further insurance I leave the windows down and after the dome light goes out I'll reach in and try the window switches.

bfellows

Thanks Alan, just what I needed! Thanks for the other input, I did forget to mention that when I remove the Battery from the car It holds charge with no issues. Just a pain up the *** to keep removing the battery - I might fit a battery isolator as a temp measure.

the flyin' scotsman

Same here.............I'll follow Alans advice later today if it ever warms up; -12C this morning.

the flyin' scotsman

We'll I went out to the car to start another diagnosis on the battery drain but its dead.........again

Getting just a little tierd of this.

Bill Ball

Alan:

Thanks for the description of the parasitic drain diagnosis. That's one to bookmark!

I've tried to do this myself, more or less doing as you advise, but I got to a stage where I believe everything you mentioned had been done or ruled out some way, but I still had excess drain. Dave A. and I ended up pulling the large connectors at the base of the CE panel until we found the culprit, then we reconnected that plug using jumpers and pulled them one at a time until we found the unfused circuit that was contributing and worked from there. Is this something we should not have had to do or could have done a different way? Just curious since you don't mention it.

bfellows

Can someone refresh my memory, is the battery negative strap supposed to be held in place with a bolt (as I have), or with a large butterfly bolt?

the flyin' scotsman

I've seen pics of both.........my car has the bolt.

Alan

Bill - what you did is pretty much the next step and often even when you narrow it down to a particular fuse you have to do similar to this anyway to further isolate

The main thing is to be really methodical and note all your findings - they won't be 100% repeatable but should be close if you ever need to backtrack & regroup. Random testing gets very confusing very fast....

Alan

Mrmerlin

one question do you see any tell tale water tracks from the bottom of the blower box? If you do its a sure bet that your getting water into the CE panel, if during your fuse pulling operation you find any corroded fuses then you should also pull every relay and with corroded connector pins should be opened get a fuse realy chart here www.928gt.com

Alan

Earlier cars had the "wingbolt" later cars just had the bolt - the wingbolt was a much better idea.

Alan