This is something I have managed to elude until now.

My car is going flat in two or Three days. I used to leave her for a couple of months and she would start right up.

The antenna is unplugged, the trunk lights are working properly (they turn of when I shut it, I Llego my phone recording inside) and I can't see any other lights or fans coming on. The only "aftermarket mods" to my cars electrical system are an alpine radio and mini amplifier that feeds of from the radio, and two powerful pusher aux fans in front on my condenser to aid with A/c cooling. These fans come on only when the compressor kicks in.

What tool should I buy to diagnose this before I take her in? I am not very familiar with diagnosing electrical problems

 

Diagnosing a drain isn't as mysterious as some people think. You will need to get a digital multi-meter with a 10 amp or better ammeter. If you need help with that, I can post some ebay links for you. But, that is step 2.

Step one: Without boring you to death about how batteries work, let me just say that batteries blow 1 of 2 ways. They either blow open, or short. A battery that starts blowing open will have great voltage, but the amperage behind it will be weak. This is typically recognizable when the weather gets cold and your car don't want to turn over.

When a battery starts to blow short, it develops an internal load that drains the battery all the time, even when it is just sitting not under any load. The first thing we need to determine is the condition of the battery. Run the car or charge the battery. Disconnect one of the battery cables and wait several days. Hook the battery cable back up. if the battery is dead, you need a new one because it is developing an internal short. If it is not, you have a drain caused by a circuit in the car and we will need to go to step 2.

 

Hey spike , you could also try the following. Buy a multimeter it doesn't need to be an expensive unit and always handy to have.
Disconnect battery negative.
Put black wire on meter into COM port
Connect black probe to battery NEGATIVE cable terminal
Connect red probe to battery NEGATIVE terminal
wait a minute or 2
set meter to amps
pull fuses out one at a time , if there is a parasitic draw the meter reading will drop showing which circuit is effected also pull relays if you do not get a drop in reading from fuses . Relays can fail to break a circuit but I would check the new installations first especially the stereo .It is a little time consuming but worth doing. I think I have covered it let me know if this confusing.

 

Lets simplify this.

Firstly you need to determine if there is too much current drain on the battery. To do this remove the negative terminal and use a multimeter on mA range, put the probes between the neg battery terminal and lead, the quiescent current draw should be under 50mA.

If it isn't then remove fuses one at a time until you find the circuit that is draining the battery.

 

I had a similar problem. I took the battery to a local parts store and had them check it under load (free test). It failed. New battery=Problem fixed.

If the battery checks out follow the aforementioned diagnostic steps.

 

Spike or Mike, whichever moniker you prefer:


Cat and other's views are very useful.


I've at least three ways to deal with electrical issue diagnostics.


1. Digital and analog VOM's sourced from HF. I'm sure that one or more exist in the greater Houston area.


2. A simple test lamp.


Protocol:


Remove the - cable from the battery. All electricals off including closed doors. Connect one of the above three in series with the - post. Minor read OK. Memory circuits active. Clock, ECU, alarm, etc.
More than about .045 MA means a circuit is closed that should not be or a low grade short.


Remove one fuse at a time, til the lamp dims or the MA's decline.
That is the problem circuit!!!


Report results and I or better electrickery guys will help.


Carl

 

Exactly.


The battery can cause the problem and is the easiest thing to rule out. Pulling fuses and relays is always my step 2. But, it is fine to start there as well. Just make sure your battery is charged before you start, or your meter will lie to you.


Something to consider... When you put a DMM in series with a battery cable, it becomes the path for all loads to receive power. As you open and close doors, trunk, hood and perform other tasks in your troubleshooting, you will introduce new loads for the meter to deal with. If you bring enough load to a meter on mA (milliamps) you will send it to that great DMM ranch in the sky. The safest bet for an inexperienced person troubleshooting something like this is to get a meter with a 10 amp hole that is fused.

 

Thanks guys. The car has eaten 2 new batteries in 3 months. I am unplugging it now because I would feel really bad askin them to warranty out yet another battery. So no tjr battery is without a doubt not the issue

 

I'm not totally sure if it is applicable to your car but have you checked the diode pack on the alternator?
As I (admittedly not very well) understand it, if the diode pack fails then the battery constantly tries to energise the windings in the alternator but it doesn't affect the alternator charging the battery so you don't get a charge warning light on the dashboard.

 

Voltages.

Charging voltage (engine running obviously) 13.8 - 14.4 depending on battery charge state.

Open terminal battery voltage (battery disconnected)
12.9 fully charged battery
12.5 50% charge
12.0 flat

The diode pack is the rectifier. Alternators generate 3 phase AC. If you have the correct charging voltage your Alternator is ok.

You need to determine which circuit is draining the battery.

Are you absolutely sure your boot lights are going out when the boot is closed.

This fault finding you need to use a meter and measure the current drawn from the battery. Around 50mA should be ok. A 50mA draw will drain 1.2amps per day from the battery.

 

Spike

Why put yourself through all that pain and suffering, not to mention the expense of keep buying new batteries.

The problem on mine, was my Car Alarm/Immobiliser and although I've now fitted a kill switch to turn off the horn, so it doesn't wake the Neighbours in the middle of the night, it still goes off and that's what drains my battery.

So why don't you do what I did and get a thing called a 'Discarnect' off ebay which will only cost you a few dollars.

I turn the battery off every time I put the Car in the Garage and I can relax secure in the knowledge, that when I turn the Battery on it will always start the Car without any problems.

Probably the best piece of Kit, that I have ever bought.

Richbrook Discarnect Car Immobiliser Battery Master Cut Off Switch | eBay

 

Discarnect kind of stinks when you constantly have to reset the clock and radio.

I'm sure you've tried it, but disconnect the aftermarket amp. That seems to be the only thing you've added. It would be a good start.

After that, you'll have to read the fuses from the different boxes around the car. I'd recommend setting something up to trick the car into thinking the doors are closed, since you'll want the car to go into sleep mode. Not sure how long some of the circuits stay active after the car is turned off. I'd give it at least 30 minutes.

 

Thanks everyone !

The Alpine radio and mini amp has been installed for well two years, but the car was at the body shop with both door panels out not too long ago. The discarnect is not an option for me. This XJS is a weekend car and has always started up even after sitting for two months. I want it to keep on doing that.

 

Craftsman Digital Multimeter with 8 Functions 20 Ranges | eBay

 

Mark,

Vee makes a good point about letting the car rest for at least 30 minutes after turning the ignition off before you try any of the current draw tests.

The most common causes of unwanted battery drain on XJSs are:

- Boot light / boot switch. Just disconnect the boot light
- Alarm system
- Radio aerial. (Something makes me think this might be unfused as well)
- Aircon fan circuits. In extremis, these can even run with the ignition off.

Good luck

Paul

 

I've used a fuse buddy to find parasitic drains. https://www.amazon.com/ESI-315-Max-F...&sortBy=recent


I have one if you want to run by and borrow it. Not far from you - I live in the energy corridor.

 

The usual trick here is to use a test lamp in series first.

If it lights up brightly, it is too soon for the DMM to be
inserted in series, except for perhaps the 10A setting.

Even then, I would want to see if I can find the cause
of the bright bulb and reduce the current flow before
proceeding.

 

If it were me Spike , I would take up pmarcian's kind offer to use his tester .I think that there is enough testing advice and I believe that you have a draw of between 1 - 2 amps , making a couple of assumptions based on the info you have given , no point going into detail .Are you charging the battery ? around 6 ( give or take ) times for a auto battery to go dead flat is about all it can take before its kaput . Once again I would be looking at the work performed on the doors although I can't think of what they could do to cause this problem . I have already been called Sherlock hehe once but my thinking is " everything fine , repairs carried out , everything not fine ! ". perhaps check with the repairer and ask if and what he did electrical wise .You would have read in this thread from another member also , if you go the DMM way set it on amps , I know you have said that your not really into electrical stuff but 1-2 amps is 1000-2000 mA.

 

10amps at 12 volts is 120watts ( a pair of headlights)

Parasitic drain is going to be in milliamps not Amps, even so the mA range on a reasonable meter is protected by 440mA fuse.

If you are worried buy a current clamp you will not blow this up.

 

Thanks everyone for your help.

With a MM it was constantly at 27 and would spike to 61 everytime the light in the lighter blinks. If I disconnect the lighter alarm light it remains at 27 even with the security system activated.

I turned the car on and turned the radio and the ac on, drove around my garage parking structure, turned the car of ,hooked the MM back up it was at 296 but quickly went back to 27 after the car sat for a minute

I don't know if that small alarm lighter light going up to 60 when it blinks is draining my battery or if I conducted these tests wrong....but since to conduct the test you have to disconnect the battery, could it not be potentially resetting the culprit by doing so?

Here is a video