Re: Question for any Motronic wizards

["Allan Williams" <allanw@xxxxxxxxxx>]

Could this be a faulty ignition switch, or some kind of ignition relay? It
would seem that if the lights come back on when it is ready to be started
that the ECU has regained it's power supply? Does the radio and other
accesories work?

I'm not sure how it's wired - does the ECU supply power to the coil, or is
it supplied straight from the key(I think it might be this way)?Anyway, you
could check if the coil is
getting power when you put the key on. If the ECU is dead and the coil is
live then it can't be the ignition. If the coil is dead too the it might be
the key or a relay. Again it depends on the ignition wiring/setup, and I'm
not familiar with the details of it.

Allan Williams.

>Date: Sun, 21 Feb 1999 11:27:22 -0500
>From: Keith Turner <kturner@domain.elided>
>Subject: Question for any Motronic wizards.
>
>   I'm having an intermittent problem with my 88 325iC.  The problem is not
>dependent on weather, speed,  amount of time the car has been running, or
>time of day :)  The car can go for a couple months with out seeing the
>problem, and then have it happen a couple times one day, then it won't
>happen again for weeks.  I'll be driving the car and then the engine will
>just shutoff.  I'll wait 10-15 seconds and it will start right up like
>nothing ever happened. There has been one or two instances where the engine
>just "blinked" off, for less than a second and then kept running. There
>have also been a couple instances where the car would not start (from being
>parked), and I had to wait for a couple minutes, then it would start right
>up.  This behavior has been going on for probably a year and a half.
>   When the engine cuts off, the tachometer drops to 0 almost instantly,
>even if the clutch is engaged and the engine is still turning.  According
>to the Eleltrical Troubleshooting manual the tach gets its signal from the
>Motronic control unit.  The only signal I see going into the MCU (with
>regards to engine speed) is on pins 47 & 48 which is the engine speed
>sensor.  That seems to tell me that even if the fuel and/or igntion
>sections of the engine had a fault that the tachometer would still work
>(provided the fault wasn't the MCU), can anyone verify this?
>  I can tell when the engine is ready to start again by the dash lights.
> The indicator lights in the instrument cluster will all turn on, just as
>if the key had just been turned to the  run position (from off).  At this
>point the engine starts with no problem. I don't know if this points to
>anything or not.  Maybe its the default startup for the MCU?
> Are there any cases in which the MCU will wait a certain amount of time to
>begin operation again (say after loss of power)?  I'm starting to think the
>problem is in the MCU, and/or wiring to/from the MCU.
> Anyone have any suggestions or information that might help me track this
>down?
>
>Thanks,
>Keith
>BMW CCA# 162807
>88 325iC
>77 320i
>

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