1992 OM602 battery drain

[southofantarctica]

Had this car for almost a year now, when I first bought it was the only time I had any battery problems with it (dead cell). I had been driving it five days a week since then as my commuter. Everything has been good up until about a week ago. I had to leave it sit in the driveway for about a month and a half due to being out of town.

When I came back and tried to start it the battery was completely flat. Jumped it and got it started, drove it for about 20 miles and parked it over the weekend. Went to start it again, no joy. Jumped it again, alternator was putting out 12.5, pulled it cleaned the contacts and the regulator. Took it up to the parts store and it tested "pass".

Put it all back together went for a drive, got home and checked output 13.8.

Moved onto battery drain, threw the multimeter inline on the negative terminal and showed 11.98(!!!!!) After checking all the fuses I was able to get it down to 10.3 after removing C and #9.

Pulled all the relays near the fuses, and the OVP with no change. Felt the starter and the wires didn't seem hot, but after taking it for a drive in 105f everything seemed the same temp.

Any pointers would be great. Also, car has aftermarket radio and a couple other random things spliced in by the PO. Haven't had time to check to see how things are wired. No alarm or anything like that, as far as I know.

[barry12345]

Disconnect the alternator. There may be some reverse diode leakage. To retain memory many car radios if not all consume an insignifigant amount of current. You almost always should check the last place you were working. So you are very unlikely to show no voltage or potential where you tested.

Rather than using voltage measurements as you did. I prefer to measure current drain. Most meters are only good to ten amps though. One can insert a resistor there. Between the negative and the ground as you did. By reading the voltage across the resistor and using a simple ohms law formula you can convert it to the current draw.

Yet you can use your system of measurement for the alternator. It is suspect. The voltage you were reading should not change if you disconnect it. If it does you do also have leakage in that alternator or regulator.

[Usaguy]

Originally Posted by southofantarctica

Moved onto battery drain, threw the multimeter inline on the negative terminal and showed 11.98(!!!!!) After checking all the fuses I was able to get it down to 10.3 after removing C and #9.

Pulled all the relays near the fuses, and the OVP with no change.

You can try pulling all the fuses not just the relays


12A of draw when the car is off is a lot (144 watts!)

[Diesel911]

I had a old Battery start my Car. I drove with non charging issues and stopped for a visit. Started normally when I left and I stopped to get something to eat.

When I was ready to leave I turned the key and nothing. I got some jumper wires to jump the solenoid at the starter and barely got a spark. Yet the Battery had 12.5 volts on it.

I decided since I was had no amperage it was the Batter. An Autozone was on the opposite corner and I bought a batter and it started right up after installation.

Charge the Battery and take it for a free load test to see if the Battery is good.

Also an alternator out put lf 12.50 is not output it is just the battery voltage.

[southofantarctica]

Originally Posted by barry12345

Yet you can use your system of measurement for the alternator. It is suspect. The voltage you were reading should not change if you disconnect it. If it does you do also have leakage in that alternator or regulator.

Just hooked it up for the test, for some reason I was reading "only" 10.34 with everything plugged in. However when I disconnected the alternator, no change.

Also, no new work has been done since around May. I have been able to leave it for over a week unattended and it would fire right up.

[southofantarctica]

Originally Posted by christuna

You can try pulling all the fuses not just the relays


12A of draw when the car is off is a lot (144 watts!)

Pulled every fuse I could get my hands on. Even the 40amp strip and disconnected the glow plugs.

It's an absurd amount of draw!

[southofantarctica]

Originally Posted by Diesel911

Charge the Battery and take it for a free load test to see if the Battery is good.

Also an alternator out put lf 12.50 is not output it is just the battery voltage.

I'll be sure to take it to get tested, but would a low charge cause me to be showing draw?

Correct, 12.5 were the initial readings. After removing the unit and cleaning the contacts and regulator it is back up to above 13.5 output.

[Usaguy]

look at page 6 of this pdf:

http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/ETM/ETM.pdf

battery power goes unfused to X4/10 (small terminal block near battery) to X4 (terminal block in the drivers footwell easy to get to) start disconnecting stuff there while watching the multimeter.

this wiring diagram has wire colors and sizes

and locations of all components

and don't forget the starter is unfused too

[97 SL320]

Originally Posted by southofantarctica

Moved onto battery drain, threw the multimeter inline on the negative terminal and showed 11.98(!!!!!) After checking all the fuses I was able to get it down to 10.3 after removing C and #9.

11.98 and 10.3 what units?

[funola]

Originally Posted by 97 SL320

11.98 and 10.3 what units?

I think he either expects you to know that since he consistently left out the units in every post thus far, or he does not understand there is a difference in Volts vs Amps!

[spock505]

The 124's are known to have consant draw over time, this can be worsened by coorded door and tailgate switches which form part of the down circuit, i.e when the car is parked with immobiliser actiavted.

Follwed all of above tips over years but still the same, tell tale sign is to unplug negative lead leave for several minutes then reconnect - best done in low light, you should see an arc along with a regulator çlick' this will fade back but does show whats'open on that circuit without ignition being on.

In the end I fitted a charging point below the bumper, pop it on chage every couple of weeks just to keep battery in good shape.

[97 SL320]

Originally Posted by funola

I think he either expects you to know that since he consistently left out the units in every post thus far, or he does not understand there is a difference in Volts vs Amps!

Given the values / 2 decimal places I can guess what method he is using, and it is still not the best way to find a drain on a system that will always have some sort of drain. ( computer and radio memories )

The method he likely isn't using is the the best way along with finding the common power connection at the battery / starter / power distribution block then separating to find what leg is causing a draw.

[southofantarctica]

Well gents, I'll be the first to say that electricity isn't my strong suit. It seems I know juuuust barely enough to get myself into trouble, but not out. While I do know the difference between amps and volts, I do owe an apology to everyone so far, as I haven't been testing things correctly. Mainly multimeter on the wrong setting, which lead me to passing out bad information and not actually testing the amp draw.

Anyways... With the thing actually reading amps I get 0.38a dram between the negative terminal and the negative cable. Much more reasonable number than the 10 amp draw I thought I had initially.

Secondly, alternator output seems to fluctuate from last readings. Today's results show 12.9v at idle and 13.2v at 2500rpms in neutral. Battery light stays off when running but lights up while waiting for the glow plugs.

Thirdly, got the battery tested and it came back as in perfect health. For giggles while I was there I had them test the alternator output on the car and it came back as having a bad regulator, even though yesterday it tested as good out of the vehicle.

Is 0.38 amp draw enough to flat line a battery in four days?

I'm out of my depth and appreciate anyone who has stuck around.

[Usaguy]

Originally Posted by southofantarctica

Is 0.38 amp draw enough to flat line a battery in four days?

Yes

.38A x 24h x 4 = 36AH

most car batteries have a capacity of 45AH so after four days it will have a low charge.

look up my post #8

or maybe start with the fuses again since you're now testing things correctly

[southofantarctica]

Went and tested the fuses again after the kids were put down, not sure why the numbers keep changing when testing the same way. Even got to the point of taking pictures of the readings for future reference.

So tonight I'm showing 0.06 amp draw (yesterday was 0.38 amps), thought it was pretty strange but decided to test the fuses. All fuses checked out good except for "C" and #9.

All fuses in = 0.06a draw.
"C" fuse removed = 0.15a draw.
"C" and #9 fuses removed = 0.00a draw.
#9 fuse removed = 0.04a draw.

(All these readings were taken multiple times with same results)

Checked for alternator output at idle again, 13.68v. Again, I'm stumped.

It seems like most of my drain is in "C" fuse circuit, right? The part that I really don't understand is why when the fuse is removed the drain increases....? Make no sense to me, but we've proven that doesn't mean a whole lot.

Also, after this short testing period I went and rolled the window up and now the passenger side works, when it didn't work yesterday. Possible place to check for my fault...?