Central locking working only intermittently.
 

I've a '93 318is, 207,000ish miles, and the central locking is starting to act weird.

The fuses are good, so that's out.

The trunk lock only actuates central locking intermittently, more off than on. Now, the door locks are starting to do similarly, but mostly they work.

I've copiously lubed and cleaned the lock mechanisms to no effect as yet. Windows work fine, no other problems I can see.

Any ideas?

The windows dont have anything to do with it.

What do you mean by cleaning the locks?

Is it one lock or the entire system?

The system is pretty simple its a solenoid activated system that moves a rod the open and closes the locks.

If its an intermittent problem its likely a ground issue.

It also could be a correded fuse holder. Locate the fuse for the circuit and clean the holder.
Even if the fuse isnt blown it can be so corroded that it esentailly acts like a resistor or a even a switch. Take a look at the blades of the fuse are they a dull aluminum color or are they shiny? Clean them with sand paper or a file. Scrape the holder as well then put the fuse back in then give it a try.



My guess is that the ground for the system is corroded, quite likely considering the age of your car.

Bostogrun identified the first suspect that you want to eliminate, but when the locks start acting hinky, and some are worse than others, it can also be microswitches. The microswitches in the door locks look just like the microswitches in the buttons on your computer mouse, and like the ones in your computer mouse, I presume that you could extend their lives for a few years by cleaning them with tuner cleaner. However, by the time I have a door apart, I have so much work invested that I am not interested in trying to patch things up, I replace all suspect electronics with new.

In the later e36 doors, they put all the microswitches inside the plug-in actuator module except for the one switch up next to the key that closes the windows when you hold the key full over. That way, when you snap in a new actuator module, you have replaced all the electronics in the door lock so whatever the problem was, if the problem was in the door, you have fixed it. In the earlier e36s, things are a little more complicated to work on, but as I recall, there is a good write-up with pictures in the 101 Projects book and web page.

Cleaning, simple. Air evacuation with compressed air, oiling with light sewing machine oil.

It started as one lock- the trunk- but has spread first to the passenger door then the driver's door.

Where is the ground?

I'll try cleaning the fuses and holder. The fuses are only a year or so old- I replace them all periodically- but who knows.