1988 535iS
Each of the terminals on the coil ( + and -) read around 12 volts with the switch on. The ignition switch causes the engine to spin, but will not start. There is no fire from the coil (to ground) when the engine is cranking.
Seems like one coil terminal gets a signal which completes a ground from the ECU to control firing...Is that right? Interestingly, another bad 059 I had on the shelf duplicates the symptoms - I wonder if there is a so called 'common-mode failure' for the BMW ECUs. Looks like I am due an ECU again - does anyone on the board rebuild these boxes? I've done the pathway to plug type fixes but have never rebuilt one of these units. Is there a consensus? Should I buy the warranted "Bosch" rebuilds - or is there a super secret source that supplies ECUs to elders, impaired, or other deserving candidates?
constant voltage at coil = ?
Yes coil (-) gets grounded by the ECM every time the coil needs to fire. Coil (+) gets constant 12V so you will see 12V at the (-) terminal also until it is grounded (which is very briefly) and hard to 'see' without a scope.
Have you tested your reference sensors on the bell housing? They tell the ECM just when to fire the coil. Then of course you need good connections from ECM to coil, etc.
If 2 Motronics exibit the same symptoms I would be more likely to suspect a problem elsewhere.
Have you tested your reference sensors on the bell housing? They tell the ECM just when to fire the coil. Then of course you need good connections from ECM to coil, etc.
If 2 Motronics exibit the same symptoms I would be more likely to suspect a problem elsewhere.
Just a matter of understanding, the coil absorbs energy when there is 12V and Gnd at the appropriate terminals. In the old days of distributors with points, this is the "dwell". The energy is released when the gound is removed, out through the spark plug wire creating a single spark to ground at the plug. This "fires" that cylinder. For the spark to get to the correct cylinder, the distributor needs to have the rotor aligned accordingly.
Applying voltage to a coil, and calling that firing, is really quite different than what actually happens.
I am just saying this because we need to troubleshoot these things without computers.... so the understanding needs to be accurate. The intention is not to be critical.
Applying voltage to a coil, and calling that firing, is really quite different than what actually happens.
I am just saying this because we need to troubleshoot these things without computers.... so the understanding needs to be accurate. The intention is not to be critical.