"won't run problems"

["Chao, Harvey" <harvey.chao@xxxxxxxx>]

To Eric Javel and others recently having problems with a no start or
intermittent running issue, who are looking and going crazy checking out
main and fuel relays, coils, crankshaft position sensors,  motronic boxes,
etc. and ad nauseum -- 

I was relaxing tonight and reading the Nov. issue of Roundel and read
Jeffrey Malter's Tech Talk input (page 111) when "the light" went on --

In addition to all the things you may have checked above and whatever else,
here Jeffrey has identified an additional one, probably frequently
overlooked. [ Of course if you absolutely  KNOW that your main relay is
pulling in, then by definition the following is NOT your problem -- note
also that the fuel pump relay is powered through the main relay contacts and
gets it's ground through the Motronic, so no main relay no fuel pump either]


If you have an OBC with the "CODE" anti theft function - according to my
electrical trouble shooting manual wiring diagrams, the "CODE" function is a
relay in series with the main relay's coil.  Normally, the OBC enables it's
own "CODE" relay which in turn enables the main relay coil.  This "CODE"
relay cycles 1 - for - 1 with the main relay.  Although it appears that the
"CODE" relay only carries enough current to run the main relay COIL, if the
contacts on the "CODE" relay get funky (and we know that over time the main
relay contacts get funky - although admittedly carrying heavier current that
will cause more pitting than just the current to run the main relay coil)
then that's a possible culprit  for the intermittent or no start condition,
just as if the main relay were funky.

Jeffery describes failure of this "CODE" relay as craning but not firing,
and the loss of power to the instrument cluster.  The Proper Name of this
"CODE" relay is:  On-Board Computer Relay Box, and in my E28 is under the
drivers side dash, next to the "chime" module and immediately below the
cruise control's control box.  According to the black and white picture, it
appears to be a black box about the same size as the light colored cruise
control box.  

Jeff describes  "... I pulled over.  Cranking in neutral, the engine would
catch, but then die again at the next bump in the road.  I knew it was the
anti-theft code relay again.  At the side of the road, I could get the motor
to fire after knuckle-rapping on the thing." He further describes that it is
very possible to jump the relay.  He describes the color code in his '85
325e-318i Electrical Troubleshooting Manual as follows:
> To jump the relay, I used a jumper wire between the green and
green-with-red-stripe wires near >the connector plug, now permanently
soldered in with spade connectors normally disconnected.  >This jumper wire
will bypass the anti-theft code relay next time it goes on vacation.  If
you're like me, >you'll wrap the dangling ends of the spade connector with
insulating tape. And make sure you >solder your connections and use
heat-shrink tubing on the bare wires.

This agrees with the color code shown in my '86 528e/535i ETM also.  The
green lead comes from the "run" side of the ignition switch and goes to one
side of the OBC CODE relay on pin 3 of connector c2.  The other side of the
CODE relay, pin 4 of C2, is the green-with-red-stripe wire which goes
through two connectors, c235 and c103 to pin 86 of the main relay (hot side
of relay coil - other end of coil is pin 85 to ground at G 103

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