1985 BMW engine shakes and loss of power

bmw
batteries
alternators

#1

I have a 1985 BMW 325e. It has about 117K miles, and te engine shakes a little when you start it up, until the car warms up (in hot or cold weather). I also have had the battery repeatedly die, (it’s a brand new battery) and am wondering if the two things might be related. The battery and alternator have tested fine in the past, but today I was driving and the car died while driving, though the battery light isn’t coming on as it usually does if battery power is low. Any ideas?


#2

These things are always difficult to determine without knowing if the problem is fuel or spark related.

If I was wild guessing (and I am :-)) and taking into consideration the vehicle age, mileage, running rough on a cold engine, and stalling on you, my guess would be that the fuel pump is on the way out.

Some more info on the battery situation would help. Is it known that the battery is going dead, or are there other factors at work here? No dashboard idiot lights, no starter solenoid click when the key is turned, dim lights, etc.

If the battery is really being drained then you may have a voltage draw in the electrical system. The first thing to always check is making sure that a trunk light is not staying on - just like your refrigerator.

You can test (sort of) for a voltage draw by making sure everything in the car is off including the key. Disconnect the battery negative cable and ever so slightly, brush the cable end against the battery terminal.
If you see a noticeable blue spark jump then you probably have a draw and have to proceed to the next step.
If you see a very faint yellow spark this is usually the clock and is nothing to worry about.
That’s pretty simplified at this point anyway and hope it helps.


#3

Hi, thanks so much for your post. I will test the things you suggested.

Some more info: when I bought the car, the check engine light was on. I have had it for about a year, and don’t drive it very frequently (less than 1000 miles a year). The battery was being drained, so I had a brand new battery put in, at which time they tested the alternator as well. It would run for a while, then if I didn’t drive it for a week or two, it wouldnt start. I had the alarm system totally removed and it was better - for a while. Then it would periodically not start (but start if jumped, and be fine for a few months).

I took it to the BMW dealership and they said that the check engine light was on due to a leaky radiator and hoses. They said the battery was dying because I wasn’t driving it often enough.

They are really expensive and as you can imagine, I didn’t pay that much for the car in the first place. I took it to my local mechanic. He replaced the radiator and hoses. That was a week ago. The check engine light was still on and I drove it for the first time, and then it died while driving - first the radio died, then the car died. This is the first time it has died while driving. The AAA guy jumped it and it started, but he said since the battery light was not on, it probably wasn’t the alternator and said that the engine shaking was troublesome and it most likely wasn’t my battery or alternator …

I know the trunk light is on when it is open - but how I check if it’s always on? how can I unplug it?

Again, thanks… perhaps this info sheds some more light.


#4

I have an 86 325es and have had similiar start up issues. This car has a cold start valve that might be acting up. There might be something causing an engine miss like improper timing, vacuum leak, tune up items, etc. Two other things cause idle issues on these cars: air flow meters and idle control valves(both of which you can pick up used & cheap on ebay.) Just curious: has anyone checked your engine mounts?

I never had any battery draining issues. It sounds yo do have some kind of an alternator issue. I did have the brushes(?) in my alternator replaced four years ago and it is still doing fine.


#5

That low mileage every year is tough on a battery as sitting idle is the worst thing that can happen to a battery.

However, a new battery should not go dead in a week or two.
If you don’t have a test light or VOM, then do as I mentioned. Disconnect the battery negative cable while everything is off, lightly touch the cable end to the battery post and note if you see a spark.
A blue one is cause for concern; it means you have a voltage draw running the battery down.
A very faint yellow spark is the clock and should be irrelevant.

A test light works better and they’re cheap. Disconnect the batt. neg. cable and connnect the test light between the cable end and the batt. terminal.
If the light is bright then you have a draw. If the light is a dim orange, then again, that is the clock and don’t worry about that.