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Electrical (including ignition)

Posted: Wed Dec 22, 2010 7:12 pm
by Jeroen
Introduction / general

Good news! Not many electrical issues! Known -but luckily minor- stuff:

-failing ignition control module due to bad ground bolt
-bad engine ground strap
-corroded fuses
-interior lighting and reverse lights failing because of short circuit on reverse light switch wire near the gearstick
-battery drain as a result of glovebox light or trunk light not being switched off

A common BMW youngtimer issue is a broken hazard light switch. It may drain your battery and if it fails, your indicators won't work either (to save you a search). Gladly you can fix it, see here: ... 9&start=26

Fusebox layout:
Indicator relay issues:

Re: Electrical

Posted: Mon Feb 04, 2013 9:29 am
by Jeroen
Ignition timing adjustment (requires ignition strobe light)

Basic mechanical setting is to set the 1st cylinder in TDC using the mark at the front of the crank (vibration damper side). The rotor arm should now point towards the notch in the housing.

First step is to make sure the static timing is spot on, meaning with the vacuum hose(s) disconnected from the ignition distributor and engine at normal operating temperature (warmed up).
M10 4 cylinder engines: 25 degrees pre ignition at 2200 rpm should give you a stable steel ball and the Z mark right next to it through the bell housing inspection hole that is located along the firewall
M20 6 cylinder engines: 22 degrees pre ignition at 1500 rpm should give you a stable steel ball and the Z mark right next to it through the bell housing inspection hole that is located along the firewall

After that you can reconnect the vacuum hoses and the vacuum advance system should be able to adjust ignition timing to the regular cold/warm situations to ensure proper running at all times.

Re: Electrical (including ignition)

Posted: Sun Dec 14, 2014 2:15 pm
by Jeroen
Alternator / battery / charging issues

Just a brief listing of checks and possible fixes. Usually this starts with either the alternator light coming on (battery symbol on the dash) or a weak battery. Please note that the alternator light comes on at a very early stage. This means that in some cases the light can already start to glow very slightly when nothing is wrong really.

No worries
When driving at slow motorway speed say 80-100kms, 5th gear so low revs, high beams and some other big power users on, then in the dark you might already see a slight glow from the charge light. No worries as this is pretty ok.

If the light comes on or you have a low or dead battery, do a few checks first:

First of all, how old is that battery? If you can open up the cells for a check, open up (beware of pressure, gases ans the contnts are acid!). What will you see? Cells not straight or fluid low exposing cells to the air. Are the battery cables connected thoroughly and no corrosing or loose contacts?

Most E21's and E30's have an extra ground strap of abt 10-15 cms long running from the alternator housing to one of the bolts that go into the engine block. Secured?
Perhaps the most important one is the chassis ground strap that hooks up to the left front of the chassis, underneath the battery tray. Undo it and check it thoroughly for corrosion. Especially the chassis is very prone to rust there so be critical!

Voltage measurements
After these checks you can perform a check on voltages. With a multimeter you can check these:
1. with the engine running you should have abt 13.8V +/- 0.5V otherwise the brushes/voltage regulator combo may be up for replacement, see under Alternator. Hint: when welding is performed, the battery should always be disconnected, otherwise the voltage regulator can blow.
2. right after you turn off the engine the battery should give you at least 13.0V imo, otherwise it is likely that you may want to replace your battery

Warning: before performing any work on the alternator disconnect both wires from the battery to be safe. After this, you can check the connections of the wires, tight enough on the alternator and on connectors? Remember what wire goes where!
How good is the belt and its tension? Does the alternator sit straight, in line with the engine so the belt runs straight as well?
Most likely and an easy check is the bracket that holds both the voltage regulator and the voltage pick up brushes (see insert below). Only two small bolts undo this bracket. The brushes should move in and out their guides easily, there should be anough length left and no corroded contacts or disconnected wires.