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[JamesH]

Okay, where do I start. I'm competent at most stuff on the Jeep but was always crap at physics and don't like playing with multimeters and stuff a lot.

I must have a small current drain on my XJ somewhere, which combined with a bit of a dud Optima is causing me hassle  :x

So, what is the best and/or easiest way to identify this drain and are there any likely suspects on a 1998 XJ 4.0l??

TIA, James


P.S. I do have, and can use, a multimeter with the right instructions  

[JamesH]

What setting would you put the meter on? I have had trouble getting a constant figure. On the 200mA setting I get a fluctuating reading from the LPG feed and similar from the main feed?

Electronics for dummies I'm afraid  

[isle of man]

james.........you have not got one of those ish meters have you?





peter henry

[greggmo]

kick out the batery  first of all and see what happens with a fresh one. this will save you a lot of dicking about and it is a good way to start the elimination prosess.

[tim_aka_tim]

To measure current, you need to be in series with the circuit under test, to measure voltage, you need to be in parallel - thats what your manual should say. You can remove the fuses and insert the probes in their place - making you in series with the circuit under test. Doesn't matter what reading you use, if your're out of range, just use the next setting up, or if it's zero, the next one down.

The alarm on my XJ uses power, and I seldom switch the engine on, so I got one of those solar chargers from Maplin for a tenner (half price at the moment). I just leave the croc clips connected across the battery - works great.

Now that's out of the way, a word of warning - digital multimeters should not be trusted to give you an accurate reading - especially voltage. Their huge restistance affects the circuit such that they look like they're open circuit, thus not registering much of a reading, if any. The relatively low resistance of an analogue AVO is much better (found this out tracing earth faults on a class 47 diesel locomotive).

[Dave69]

An AVo meter as said is the best for fault finding as it is nice and sensitive. The digital multimeters are great for quick answers but the signal is manipulated so the readings are easier to read, not by much but enough to possibly cause a problem depending on how detailed you want  an answer. The old dial gauges are better but can take some working out with the multi display

[JamesH]

The battery goes back today so I guess it'll be after Crimbo until it's all done.

Just one last question if I may - when testing for current (ignition off) do I need to wait a period of time or discharge any current 'floating around' after switching the engine off, before testing?? I've either got a crap multimeter, shagged it somehow or am doing something wrong.

Ah well, merry Christmas everybody  

[Mike Pavelin]

If you are measuring ignition off drain on a Jeep, you obviously have to have your multimeter set to Amps DC, on the highest setting (usually 10A) and connect it in sieres with the battery (+ terminal to the battery + post, - terminal to the removed battery + cable) and put a 10A fuse in the line if the meter isn't fused to protect it.
You really need to measure this with the Jeep in a 'parked' condition so make sure everything is turned off, the doors are all closed and the bonnet light disconnected. Preferably, the vehicle should be locked and as well. Because the central locking uses so much juice it'd blow the 10A fuse, so the trick is, to hook up the meter in sieres with the battery cable, keep it in line, but bypass it with a jumper lead until you've locked it with the remote, then remove it. This will allow you to observe the current draw as the computers start to shut down. The system should settle after a few minutes.  If an alarm is fitted, disconnect the wire from the bonnet switch so it thinks the bonnet is closed or it'll go off.
After a few minutes the reading should stabilise. If you remove the IOD fuse (Ignition Off Draw) you should see a fall in the current draw as this fuse isolates most of the systems that are powered direct from the battery. You will still see some draw as the battery has to hold up the memory on the electronic control modules for various other systems.
For those who own Jeeps of this era, they all have quite a large permanent current draw, and the owner's handbook actually states that if a vehicle is to be left unused for more than 6 (IIRC) weeks, the IOD fuse should be removed to preserve the battery. I seem to recall 100-150mA is not unusual.

[JamesH]

Thanks Mike, will get get testing when new battery arrives.