From digest.v7.n741 Wed Dec 10 04:17:15 1997
From: Jim Cash <j.cash_at_sympatico.ca>
Date: Tue, 09 Dec 1997 22:43:01 -0500
Subject: Cold Start Problem ?
Following up on some dialogue between Vlad and Al Sutlick.....
> >It looks like my cold start injector never turns on.
> >I checked the voltage in the wire that goes into the injector
> >and it's always 0. Does anyone know what activates the injector,
> >and where the power source is? (is there a relay or a fuse or a ...)
> >Thank you,
> >'79 Euro
> I'll take a look at my ETM, hopefully later today and see what I can come
> up with; it covers our early Euros, exclusively. I've replaced my cold
> start injector once in the nearly five years that I've owned the car; it
> cured a tough cold-start problem totally.
> Al Sutlick
For what it's worth, I'll jump in with some info, based on experience
with an 82 528e.
Every 4-6 months I would experience the dreaded "crank, maybe sputter,
but no start till after 15-20 seconds of cranking". If it was really
cold it would not start at all.
My problem was never the injector, but the "thermo time switch" that
This switch is usually located in the thermostat housing - large sensor
unit with electrical connector on the top, and a large brass nut as the
I will explain how it works on the 82 528e - others are similar, but may
When the ignition switch is in the "start" position it sends battery to
the cold start injector (black/yellow wire).
With an automatic transmission this lead first passes through the make
contacts of the "start" relay - which operates from the same battery and
gets its operating ground from the "P" or "N" leads at "transmission
Now to explain the control of the injector - the thermo time switch.
The other injector lead (white, or black/red) gets a ground through the
"normally made" contacts of the thermo time switch. The ground does not
come from the other wire on that switch, but internally from the case of
the switch being grounded on the metal coolant housing.
So the injector operates when the ignition switch is in "start", and the
contacts are made in the thermo time switch (and also the start relay
The thermo time switch has it's contacts closed only when the coolant
temperature is below 59F (15C). So the injector should never operate if
the coolant is above that temperature. This is the "thermo" part of this
But there is another wrinkle. If that cold start injector fires too long
it floods the engine. So, there is another feature of the thermo time
switch (the "time" part) to prevent this.
There are 2 wires on that switch, and the second one (black/yellow) is
bridged to the one from the ignition that goes to the injector. So, when
the ignition is in the start positon, battery is also feed to a small
resistance heater in the thermo time switch. This heats the internals of
the switch and when it reaches the 59F mark the contacts open, and the
injector stops operating.
Depending on the coolant temperature, and how long you are cranking, the
injector may, or may not be firing, regardless of outside temperature.
So - that is how it supposedly works.
NOW - what can go wrong?
Injector - Pull off the connector and touch battery and ground on the
injector terminals. If you hear it clicking then it is OK (unless it is
plugged which is unlikely). Usually these leak more often than fail to
Thermo Time Switch. - I was told that that is a "mercury" relay. My
experience with these is that they fail occasionally due to a build up
of contamination on the contacts.
Temporary solution - strike the base of the switch with a small hammer -
3-4 light taps to jar the contacts & clear the crud - works every time.
Really impresses your passengers when you jump out, thump it a few times
and it fires right up. Seems to last 2-4 months till you have to grab
the hammer again
Longer term solution (short of replacing the switch) is to remove the
electrical connector and apply 10-12 volt AC across the contacts for
about 10 seconds. This always cured mine for about a year.
My recommendation is to use the "knock" as a temporary solution and then
get a new switch. Easy to install. Just remove the old and screw in the
new. Coolant will not leak out as long as the rad cap is in place due to
Soooooo, for what's worth, now you know how to "knock up" a bimmer.
OK - that has a different meaning in England - but it still applies "any
Dat's it - eh!
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London, Ontario, Canada
BMW CCA 102929
E39 '97 540iA