Car won't start

[Supercar]

Ok... This might not be NSX related... hence, its in the off topic thread. And this is not about an NSX but I decided to post it in here anyway since NSXprime is the best auto website in the world with a bottomless wealth of information.

Anyway, I own a Mercedes Benz 190 (from 1988) which will not start after about 5 days of not driving / starting it. I have changed the alternator to a new one and this 'dead battery symptom after 5 days' is still there. I suspect there must be some kind of a tricke discharge from the battery. Where should I look first?

Thanks for any suggestions.

 

[sahtt]

Not to sound pessimistic, but these problems are often quite difficult to diagnose.

In the mean time, you can simply detatch the negative battery cable if you know you will not be driving the car for a couple days.

I can't off much advice as I'm not familiar enough with 1988 MB's to tell you where to start diagnosing besides checking to see if the load the battery is above normal while it is off. At least that will give you some evidence it is indeed a component drawing too much current [dome light for instance].

 

[robr]

A general troubleshooting technique might be to take a volt meter to the battery to see if there is substantial draw with the car off. If there is, you can start pulling fuses one at a time to see if you can narrow it down to a specific circuit causing the problem.

 

[Carguy!]

A new battery would be the first thing I looked at if the battery was pretty old.

Next hook up a simple car maintenance charger and plug the car in if you aren't going to use it for a few days. This is easier than disconnecting the battery as they normally provide a cable you can route to an accessible spot and plug it in in a couple of seconds.

 

[SENNAF1]

Sounds like a ground problem.As posted can be like chasing your tail.

 

[Supercar]

Thanks for all the views. I agree, trying to diagnose this problem is like chasing shadows :frown:

However, I have plugged a voltmeter to the battery when the car is off (and the battery is still connected). The reading shows 12.5 - 12.6 v. What type of changes should I expect to see by pulling the fuses off one by one?

Thanks

 

[robr]

My mistake, you want to look at amperage draw from the battery. You need an ammeter, not a voltmeter .

 

[Supercar]

Done the ammeter testing and found no significant jump in reading. Brought the car to a mechanic and he says that my battery shouyld not be rated at 66. It should be higher i.e. in the 70 - 80 range. Is this true? He mentioned that the 66 battery is not sufficient to keep all the 'power' to kick the benz into life. Hence, the dead battery scenario.

Btw, the current battery is a new maintenance free battery.

Thx